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Insect traps tested as an aid to pest management in milled rice stores
J.srored Prod.Res. Vol. 21, No. 4,pp.215-229.1985 PrimedinGreatBritain
INSECT TRAPS MANAGEMENT
0022s474X;85 $3.00+O.OO Pergamon PressLtd
TESTED AS AN AID TO PEST IN MILLED RICE STORES
R. J. HODGES*, H. HALID?, D. P. REES*, J. MEIK* and J. SARJONO~ *Storage Department, Tropical Development and Research Institute, London Road, Slough SL3 7HL. Berkshire, U.K. and tBadan Urusan Logistik (BULOG). Jl. Gatot Subroto 49, P.O. Box 2345, Jakarta, Indonesia (Received 25 June 1985) Abstract-Various insect traps were tested in a milled rice store, in Indonesia, with a view to developing an insect trapping method that would enable estimates of insect populations to be obtained reliably and easily. These estimates might then be used to predict the optimum timing for pest control measures. The trial was conducted over a 7 month period in a store containing 4 bag stacks of polished rice. Trap catches were compared with population estimates obtained by sifting the contents of bags selected from all regions of the stacks and by very extensive, monthly spear sampling of outer bags. The insects observed to occur most frequently in the store were Sitophilus zeamais, Ahasverus advena, Tribolium castaneum, Oryzaephilus surinamensis, Typhaea stercorea, Carpophilus pilosellus and Xylocorisjlavipes. The precision of the spear sampling method for these species was estimated; large numbers of samples (200+) were usually required to obtain population estimates with a reasonably high degree of precision. The insect traps indicated population changes that were roughly in proportion to those indicated by spear sampling. The most useful of the traps tested was a bait bag containing brown rice milled from local rough rice. For monitoring insects in milled rice stores this trap would have several advantages over extensive spear sampling-it is positioned and retrieved more easily, the extraction of insects from it is very simple and, unlike spear sampling, it does not damage sacks. Further research is required to test traps in operational stores, particularly to establish the relationship between trap catches and the actual insect population so that trap catch thresholds may be set. Control techniques could then be applied when trap thresholds are exceeded, avoiding unnecessary treatments and optimising control.
INTRODUCTION
Insect infestation of durable, stored products may cause serious nutritional and financial losses. In order to determine how much the produce is at risk, it is important to be able to assess objectively the size and distribution of infesting insect populations. This knowledge should permit the correct timing of pest control measures so that they are applied neither too early nor too late. However, quantitative assessments are difficult to achieve; as Howe (1966) noted, there are “two difficulties, that of detecting insects . . . and that of placing an accurate numerical estimate on data subject to such an uneven distribution”. Monitoring insects in stores with traps has, for the most part, been restricted to qualitative assessments or an early warning of the insects present. Most of the common monitoring techniques were described by Ashman (1966) although important recent developments include pheromone traps (Brady et al., 1971; Burkholder, 1976) and various bags containing food baits (Strong, 1970; McFarlane and Warui, 1973; Pinniger, 1975; Pinniger et al., 1984). Quantitative determinations of insect populations in stores are almost invariably made using spear sampling, which is likely to give reliable results only when the sampling is so extensive as to require numbers of samples that may well be impractical in operational stores. For pest management purposes, quantitative determination using traps has been reported only for moths, with either light traps (Kirkpatrick et al., 1972) or sticky traps baited with synthetic sex pheromones (Hoppe and Levinson, 1979; Reichmuth et al., 1980). The purpose of the present study was to identify an insect trapping technique likely to give reliable quantitative data on which pest management decisions in milled rice stores can be made. A 7 month trial was undertaken to test several different types of trap in a bagged rice store in Indonesia. Estimates of the insect populations were made at intervals during the study by breaking down stacks and sifting the contents of bags, selected from all regions of the stacks, and by very extensive spear sampling of outer bags. These estimates were compared with the catches of various traps to determine how well the traps performed. 215
216
R. J.
MATERIALS
HODGES
AND
el
al.
METHODS
General
The test was performed over a period of 7 months at Tambun (West Java) in a store dedicated exclusively to this study. The store was a small open-eaved godown with concrete floor and corrugated iron walls and roof. It had no windows, stood 7 m up to the eaves and covered an area of 290 m’. Four bag stacks (Fig. 1) of polished rice were built in the store using 100 kg bags. Each of the four stacks (A-D) consisted of about 600 bags (60 tonnes) of rice in 13 layers. All bags were coded with coloured tags so that, if moved, they could be replaced in the same position. The tags on the outer bags of each stack, up to the 7th layer and also those on top of the stack, were numbered. This numbering enabled bags to be selected at random for spear sampling. The store was kept closed and undisturbed between sampling intervals. Insect numbers increased rapidly from the start of the test. In order to avoid excessive losses it became necessary to fumigate the rice. No attempt was made to control insects in the fabric of the store. At the end of week 8, the test was suspended for a total of 4 weeks. Two stacks were broken down and insect numbers assessed (see below), then rebuilt for the fumigation, which was performed for 1 week under gas-tight sheets with two Phostoxin tablets/tonne. One week later the sheets were removed and the test was resumed. At the start of the test the moisture content of rice samples, taken from 2 bags at each side of each stack, was determined using an Iseki-Rika resistance type meter. The mean (+ SD) moisture content was 12.62 k 0.42%; the moisture content of samples taken from the same bags at the end of the trial had risen to 13.70 +_0.16%. A thermohygrograph placed at the centre of the store, for the duration of the test, recorded a regular night/day temperature fluctuation of approx. 25-33°C. Bag analysis
When the bag stacks were built at the start of the trial, samples of 5 kg were taken from 10% of the bags going to each stack and sifted to give information on insect numbers. The bags subjected to this analysis were clearly marked and allocated at the rate of 4-5 to each layer of each stack and were distributed evenly between the outer, middle and inner regions of each layer. To record population changes with time, the examination was repeated with the same bags in stacks A and C at 8 weeks after the start of the test, the stacks being rebuilt just before fumigation. Immediately after fumigation the stacks were assumed to be free of insects. A further population estimate was made after 7 months, at the end of the test, with stacks B and D.
Stack A
I 1-4.9-12 trop positions on top of stack on &or c+rs3
Fig. I. Location shown
trap positionson
side of stock
of bag stacks (A-D) and trap positions in the experimental store. The trap positions for stack B were repeated, with the same orientation, for the other 3 stacks.
Insect traps
217
The examination of bags for insects was performed as follows: (1) In order to obtain a large representative sample from each 100 kg bag, the contents of each were passed through a Produce Flow Sampler (PFS) (Golob, 1978) set to extract a sample of about 5 kg. The residue from the sampler passed into an empty hessian bag. (2) The 5 kg sample was passed through a TPI Sack Sieve (Golob, 1978) with sieve apertures of 2.0 mm. This removed most of the insects, which were then identified and counted. (3) Both the insects and the original rice sample from the PFS were returned to the 100 kg sack from which they were extracted. The sack was sewn up. @ear sampling
At the end of each 4-week period, spear samples of 130-16Og of rice were taken from 50 randomly selected bags from each stack. The sampling spears employed were of the type used by BULOG* and were straight cylinders about 45 cm in length with an i.d. of I .5 cm. The numbers and identity of the insects in each sample were recorded. The precision with which the monthly spear sampling results estimated the population of each insect species present in the store was determined by estimating the number of samples required to give a standard error amounting to 10 or 15% of the sample mean. These estimates were made only for those months in which there were sufficient numbers of a particular species for a useful analysis. The first stage in the analysis of each set of monthly sampling results, pooled from all 4 stacks, was to fit a negative binomial distribution by the Maximum Likelihood Programme (MLP) (Ross, 1980). Chi-squared values for goodness of fit showed that discrepancies between the observed and expected values were significant (P < 0.05) for only 3 data sets out of 28, namely for Oryzaephilus surinamensis (L.) during the first month, Xylocoris JEavipes (Reuter) during the second and Carpophilus pifosellus Motschulsky during the fifth month. Mostly, negative binomial distributions fitted the data very well. Using values obtained from the fitted distributions, the sampling precisions were determined by the method described by Finch et al. (1975), where the number of samples required (ns) to achieve a mean with standard error of loop% is given by
where K is the dispersion parameter of the fitted negative binomial distribution and A4 its mean. The value of l/K has also been used here as an index for comparing the degree of dispersion, within the store, of the various insects. High values of l/K indicate low dispersion, i.e. aggregation. Refuge traps
These consisted of a strip of single layer corrugated cardboard (36 x 9 cm) folded into to give a 9 cm square (Burkholder, 1976). In order that insects should die on entering the corrugated inner layer was sprayed with a wettable powder formulation of (pirimiphos-methyl) at the rate of 1 g of active ingredient/m3. During the study there obvious repellency effects due to this treatment.
4 layers the trap Actellic were no
Pheromone traps
Each of these consisted of a refuge trap, as described above, with a plastic pheromone capsule (4 x 0.5 cm) at the centre. The pheromones used were either “Dominicalure l”, an aggregation pheromone of Rhyzopertha dominica (Fabricius) (Williams et al., 1981), prepared as described in Hodges et al. (1983) or the aggregation pheromone of Tribolium castuneum (Herbst) (Suzuki, 1981). The latter, 4,8_dimethyIdecanal, was prepared as a racemic mixture of isomers by a 7-step synthesis from 3-methylglutaric acid (Fig. 2). All the steps in the preparation were straightforward to carry out and gave products which were purified by simple distillation without the need for chromatography. Analysis of the product by capillary gas chromatography showed a single sharp peak with less than 2.5% of any single impurity (25 x 0.32 m i.d. fused silica capillary column coated *Badan
Urusan
Logistik
= National
Logistics
Agency.
218
R. J. HODGES~1 al
Fig. 2. Synthesis of 4,8-dimethyldecanal. Reagents: (i) BIH,: THF; acetic anhydride-pyridine; (ii) HBr-acetic acid; (iii) 2-methylbutylmagnesium bromide-Li&uCl,-THF; (iv) KCN-I8-Crown-bCH,CN; (v) KOH-EtOH-H20: (iv) B2H,,: THF; (vii) pyridinium chlorochromate-CH,C&.
CP Sil 5CB, helium carrier gas 0.5 kg/cm’, splitless injection at 55°C for 2 min, and then programmed at 4”C/min). The mass spectrum was identical with that reported by Suzuki (1980, 1981). The 4R, 8R isomer of 4,8-dimethyldecanal has been shown to be the most active isomer in electroantennogram and bioassay tests against T. castaneum and to be equal in activity to the natural pheromone (Suzuki and Mori, 1983; Levinson and Mori, 1983). The mixture of all 4 isomers was shown to be between T_:and h as active as the natural pheromone (Suzuki, 1981). The pheromone capsules were loaded with 1 mg of either pheromone. A fresh pheromone capsule was used each week of the study. with
Bait bag traps
These consisted of a plastic mesh (Netlon Limited, Blackburn, U.K.) envelope (8 x 16 cm). The mesh had twenty 2.0 mm apertures/cm2. The envelope was filled with approx. 60 g of either a bait consisting of equal parts of wheat, peanuts and kibbled carobs (Pinniger, 1975) (=MAFF Bait Bag) or brown rice milled from local rough rice (gabah). It was then closed with staples. The traps were disinfested after use by freezing for 1 week. The food in the traps was changed after 2 weeks use. Pitfall traps
These consisted of a 5 x 2.5 cm glass tube. the outer side of which was covered with filter paper. The paper enabled beetles to climb the outside of the tube and, as it protruded over the mouth of the tube, beetles reaching the top could fall in. The smooth inner surface of the tube prevented the escape of those beetles unable to climb glass. The traps described above were located in four positions on top of each stack, on the sides of each stack and, except for pitfall traps (which were easily knocked over) in four positions on the floor (Fig. 1). When traps were placed in the side of stacks they were pushed into the crevice between bags and when on the floor they were located almost in contact with the wooden pallets at the base of each stack. On the floor and on top of stacks the traps were lying with their upper surfaces exposed. Only one of the four types of trap was located on a stack at any one time and traps were changed at weekly intervals. Each of the four traps was deployed on a different stack each week for 4 weeks, giving a convenient 4 x 4 latin square design. A fresh square was used for each month of the trial. Bait bags and pheromone traps both existed in two forms; both forms were used on the same stack in equal numbers, occupying all odd-numbered or all even-numbered trap positions (Fig. 1) alternately. RESULTS General
A full list of the insects observed in the store during the study is given in Table 1. Less than half of these species occurred frequently enough to be given detailed consideration. The experimental results for these species, with the exception of the Psocoptera which were not counted, are presented in Tables 3-10 and Figs 3-10. Tables 3-10 give the mean catch per trap for each
Insect
traps
219
Table I. Insect species observed in the experimental store during the 7 month trial, September 1983 to March 1984 Coleoptera Anthicidae Anthicus sp. Bostrichidae Rhy:opertha dominicu (F.) Cucujidae Cr_vptolestes,ferrugineus (Stephens) Cryptokstes pusi/lus (Schenherr) Curculionidae Sitophilus xwnai.s Motschulsky Mycetophagidae Typhaea .stercorea (L.) Nitiduiidae Carpophilus pilosrilus Motschulsky Silvanidae Ahasoerus adwna (Walti) Oryraephilus surinamensis (L.) Tenebrionidae Tribolium castaneum (Herbst) Lathe&us orwae Waterhouse Alphitobius diaperinus (Panzer) Palorus ratxburgii (Wissmann) Palorus genalis (Blair) Trogossitidae Tenebroides mauritanicus L. Lepidoptera Pyralidae Phycitinae Ephestia cautella (Walker) Plodia interpunctella (Hiibner) Galleriinae Corcyra cephalonica (Stainton) Hemiptera Anthocoridae Xylocoris flauipes (Reuter) Psocoptera Liposcehdae Liposcelis entomophilus (Enderlein)
species, over the whole 7 month trial, at each of the three trap positions, i.e. the top or sides of a stack or on the floor. Figures 3-10 show, for each species, the mean monthly trap catch, calculated excluding those trap positions that consistently gave poorer results, the mean numbers from the 200 spear samples per month and the insect population as estimated by bag analysis. The shapes of the curves drawn between points on the bag analysis graphs are based on the spear sampling results. However, as spear samples could be taken only from outer bags, the shape of these curves must be regarded as largely speculative. Spear sampling
The monthly spear sampling results are shown in Table 2. For the species Ahasverus advena (Waltl), T. castaneum, 0. surinamensis and X.Javipes, the values of l/K were small, i.e. the insects were fairly evenly distributed in the store and the use of a 200 sample size would seem to have been adequate for estimating their populations during most of the test since this number of samples would give a mean value for the population with a standard error of within l&15%. Over much of the study, the mean numbers of Sitophilus zeamais Motschulsky were comparable with at least those of T. castaneum; however, its distribution was considerably more aggregated. This was shown by the values of l/K which were as much as three times as great as the values for T, castaneum. During the first and second months of the trial, the 5’. zeamais population was sampled with a precision of about 15%. After fumigation, the number of samples taken was clearly inadequate for a reasonable degree of sampling precision. This was also found with C. pilosellus and Typhaea stercorea (L.) (Table 2). Insect trapping Sitophilus zeamais. Traps placed on the floor of the store gave somewhat greater catches than elsewhere (Table 3). During the first 2 months, captures by all the types of trap increased roughly
I.10 +0.10
I .99 2 0.20
T. cm~nneunr
A. odwna
poaipes
-Insufficient
x.
C. pilosdus
numbers
244
-
-
193
I79
213
540
10%
for useful analysis.
I.17 kO.13
-
0.68 * 0.08
0. surinomen.sis
T. ,s,ercoreo
1.11+0.19
species Mean+ SE
I
107
-
-
85
79
120
240
15%
6.04 kO.37
1.69~0.16
0.86 + 0.09
77
I80
236
186
41 I
10%
Top Side Floor
Trap position
MAFF bag 1.03 f I.15 f I .77 f 3.1 I.0 4.2
bait
0.60
-
-
I.21
I .20
0.84
3.47
UK
0.49 + 0.10
0.46+0.1?
I.01 kO.16
I.21 ro.13
_
Mean + SE
5
807
1215
505
238
10%
degree of population IO or 15%
387
539
224
I05
15%
aggregation
-
6.60
10.00
4.06
1.56
-
~
l/K
0.42 + I .5 1.33 f 3.0 3.0 f 6.6
Brown rice bait bag
Trap
<0.05 0.23 f 0.8 I .65 + 5.2
Rhymperrha pheromone
0.08 k 0.5 0.17 +0.6 0.8 + 2.0
Tribolium pheromone
type Refuge 0.135+0.6 0.22 * 0.7 I .25 + 3.9
586
875
422
I32
223
470
1268
6 ~ 10%
0 <0.05
Pitfall
260
385
I86
58
99
208
563
3.30
6.80
3.1 I
I.19
1.56
0.30 + 0.06
0.33 & 0.13
0.56 i 0.1 I
3.93 * 0.44
0.65 i 0.09
0.97+0.12
I .99 * 0.32
I I.23 3.57
Mean k SE
881
24X
803
233
357
315
484
10%
1
353
104
I59
140
215
15%
391
5.31
21.27
6.28
2.08
2.04
2.12
4.34
I/K
precision
IO65
to gwe a sampling
I/K
of spear sample\
..~ 15%
number
trial in various
0.39 k 0.06
0.52 * 0. I I
0.99*0.15
7.43 f 0.62
1.49_+0.16
0.88 ? 0.14
0.69+0.18
Mean + SE
(l/K) and the required
of adult Silophilus xamais captured during the 7 month on the top, sides, or on the floor around 4 bag stacks
34
79
104
82
I81
15%
Table 3. Mean numbers (*SD) traps located
0.29
-
-
I .43
0.88
0.97 f 0.09
I.57 + 0.22
4.54
1.26
Mean + &
2
spear sample<. the observed
VK
(k SE) of insects from 200 monthly
s. xaml7i.i
Insect
Months:
Table 2. Mean numbers
of
221
Insect traps
I I
I
I
I I
Spear
I I
I I
lropping
I
n 0
1
I
I
I
2
sampling
3
5
6
7
M&S
Fig. 3. Population estimates for adult Sitophilus zeamais from bag analysis, spear sampling, and insect trapping over the 7 month trial. The histogram bars for insect trapping, from left to right each month-MAFF bait bags, brown rice bait bags, Rhyzopertha pheromone trap, Tribolium pheromone trap, refuge trap.
in proportion to the population increases suggested by spear sampling and bag analysis (Fig. 3). After fumigation, only the bait bag results maintained a constant proportional relationship with the spear sample results (Fig. 3) although during this period the number of spear samples taken was generally inadequate to give a high degree of precision (Table 2). Except in the fifth month, the bait bags filled with brown rice trapped consistently more S. zeamais than those with the MAFF bait (Fig. 3). After fumigation both the insect traps and spear sample results suggested a greater population of S. zeamais than would have been expected from the bag analysis results. In view of the aggregated distribution of S. zeamais demonstrated by spear sampling (Table 2), it would seem likely that during the bag analysis a rather low proportion of infested bags were sifted; this would give rise to a low population estimate. Oryzaephilus surinamensis. Trap catches from the top and sides of the stacks and the floor gave similar results (Table 4) and all traps were fairly effective in monitoring the pest (Fig. 4). After fumigation, the MAFF bait bags proved to be the most effective traps and captured some beetles
Table 4. Mean numbers (I SD) of adult Oryraephilus surinamensis captured during the 7 month various traps located on the top, sides, or on the floor around 4 bag stacks
trial in
Trap type Trap
position
TW Side Fl00r
MAFF
bait
Brown
rice
bag
bait bag
0.46 2 0.9 0.7 + 1.2 0.6 + I.2
0.31 k 0.6 0.53 i_ 1.4 0.48 * I .2
Rhyzoperlha pheromone < 0.05 0.29 & 0.9 0.72 + I .9
Tribolium pheromone
Refuge
Pitfall
0.16kO.5 0.25 2 0.9 0.48 + 0.9
0.23 rt 0.6 0.09 i 0.4 0.47 & 2.0
to.05 co.05
222
R. J. HODGESet al.
1.1
p 0.9 e > 0.6 ? SO.3 z 0 1
2
3
4
5
6
7
MONTHS
Fig. 4. Population estimates for Uryzaephilus surinumensis from bag analysis, spear sampling, and insect trapping over the 7 month trial. The histogram bars for insect trapping, from left to right each month-MAFF bait bag, brown rice bait bag, Rhyzoperfha pheromone trap, Tribolium pheromone trap, refuge trap.
during the fifth month when other traps failed to catch any. Catches from all traps were roughly in proportion to the population changes indicated by spear sampling and bag analysis (Fig. 4). Tribolium castaneum. The mean trap catch data in Table 5 show clearly that the pitfall traps did better on top of the stacks, the bait bag and refuge traps did better on the tops and sides of stacks, and the remaining traps did about equally well in all three positions. Bag analysis suggested that during the first 2 months there was a slight increase in population (Fig. 5). In contrast, the spear sampling results suggested a decrease of about 23%. The trapping results did not resolve this confusion as the bait bags and pitfall traps indicated a slight decrease in population while the pheromone and refuge traps suggested a slight increase (Fig. 5). After fumigation, the results were easier to understand. The population changes indicated by spear sampling were roughly in proportion to those suggested by the trap captures, particularly those from the bait bags and pitfall traps (Fig. 5). It was disappointing that the specific Triboiium pheromone traps captured so few beetles.
Table 5. Mean numbers (+ SD) of adult Tribolium cusmmnn captured during the 7 month trial in various traps located on the top, sides, or on the floor around 4 bag stacks Trap type Trap
position Top Side Fl00r
MAFF
bait
Brown rice
Rhy:operrha
bag
bait bag
pheromone
29.27 + 33.9 26. I4 + 32. I s.25 + 8.2
12.62 k 12.1 13.45 + 13.3 6.20 + 5.9
2.45 k 2.2 3.45 ? 3.3 2.33 + 2.0
Tribolium
pheromone 4.69 + 3.4 4.96 f 3.9 4.54 f 3.3
Refuge 3.5 * 3.8 3.25 + 4.3 1.8 + 2.3
Pitfall 17.57 * 19.0 8.83 f 7.5 -
Insect traps
223
Table 6. Mean numbers
Ahasverus advenu. Trap catches on the floor and the top and sides of the stacks were all of similar size (Table 6). All traps were effective in catching this beetle although the bait bags were especially good after fumigation (Fig. 6). At the start of the test the A. adwnu population was relatively high but all traps and the spear sample results subsequently indicated a decline in the population size. The extent of the decline was so great that at the bag analysis just before fumigation no A. advena were detected (Fig. 6). The MAFF bait bag gave an early warning of this pest after fumigation and indicated a progressive population increase from the fifth month to the end of the trial. The other traps, except the brown rice bait bags, indicated a progressive increase from the sixth month (Fig. 6). With the brown rice bait bags. the population dropped slightly between the sixth and seventh months. Spear sampling showed a greater drop in the same period, at a time when the precision of spear sampling was high (Table 2). One explanation for the difference between the spear sampling results and trap catches. except those for the brown rice bait bags, could be that during the seventh month A. advena adults were distributing themselves from the stacks. This would lead to higher trap catches but
MONTHS
Fig. 5. Population estimates for Triholium ~u~tmaun from bag analysis, spear sampling, and insect trapping over the 7 month trial. The histogram bars for insect trapping, from left to right each monthMAFF bait bag, brown rice bait bag. R/r~zoper/h pheromone trap. Tribolium pheromone trap, refuge trap, pitfall trap.
R. J. HODGES el al.
224
MONTHS
Fig. 6. Population estimates for adult Ahasoerus adwna from bag analysis, spear sampling, and insect trapping over the 7 month trial. The histogram bars for insect trapping, from left to right each month-MAFF bait bag, brown rice bait bag, Rhyzopertha pheromone trap, Tribolium pheromone trap, refuge trap.
lower spear sampling results. This explanation is consistent with the relatively low bag analysis result recorded at the end of the trial, which was smaller than might have been expected from the trap and spear sample results. Typhaea stercorea and Carpophilus pilosellus. Both species were encountered only rarely before fumigation. After fumigation, they became very much more numerous (Figs 7 and 8) possibly due to the rise in ambient humidity that came with the onset of the main rainy period during the fourth month of the trial. They entered traps most frequently when these were placed on the floor (Tables 7 and 8). Only the bait bags captured any appreciable numbers of T. srercorea or C. pilosellus. For both species, the proportional changes in population suggested by trap catches coincided with those indicated by spear sampling (Figs 7 and 8) despite the generally low precision with which the spear samples estimated the populations (Table 2).
Table 7. Mean numbers (k SD) of adult Typhaea stwmrea captured during the 7 month trial in various traps located on the too. sides. or on the floor around 4 bae stacks Trap type Trap position
MAFF bait bag
Brown we bait bag
Rhyroperlha pheromone
Top Side Floor
6.4 +_7.2 9.4* 13.8 23.34 + 69.2
1.37 * 3.8 0.156+0.45 9.45 + 16.1
0 co.05 < 0.05
Tribolium pheromone 0 CO.05 CO.05
Refuge
Pafall
0 <0.05 co.05
< 0.05 <0.05 -
Insect
225
traps
-_u_
Trapping
MONTHS Fig. 7. Population estimates trapping over the 7 month
for adult 7’yphuea srerc~reu from bag analysis, spear sampling, and insect trial. The histogram bars for insect trapping, from left to right each month-MAFF bait bag, brown rice bait bag.
The numbers encountered in the spear samples and bag analysis were much smaller than the numbers of both species extracted from the traps (Figs 7 and 8). It can only be assumed that the populations of these beetles did not penetrate the bags and were mostly localised on bag surfaces or on store structures. Rhyzopertha dominica. R. dominica was present in the store at very low population density. It was captured only in the specific Rhyzopertha pheromone baited trap and in the brown rice bait bags. In both of these types of trap, the catches were fairly evenly distributed between the three trap positions (Table 9). Owing to the very low population present in the store, the trap catches were very variable (Fig. 9). No individuals of this species were detected in spear samples and only during the first 2 months was the beetle found during bag analysis. XylocorisJEavipes. X.Jlavipes is a predator of stored products pests. Its presence in traps in large numbers would indicate that a significant pest population exists in a store. X.javipes was captured frequently in the traps (Fig. 10) and there was no clear distinction between trap catches from the three trap positions (Table 10).
Table
8. Mean
(*SD) of adult Carpophilus pilosellus captured during the 7 month trial in various traps located on the top, sides, or on the floor around 4 bag stacks
numbers
Trap type Trap position -fop Side
Floor
_~.
MAW bait bag
Brown rice bait bag
Rhyzopertha pheromone
Tribolium pheromone
Refuge
Pitfall
5.43 + 12.7 13.96 k 29.0 48.03 + 57.7
3.0 + 6.7 4.03 * 8.9 48.51 f 67.3
<0.05 0 <0.05
<0.05 <0.05 0.21 f 0.6
0 < 0.05 <0.05
0 < 0.05
226
MONTHS Fig. 8. Population estimates for adult Curpop/~ilu.s prhe/lrrs from bag analysis. spear sampling, and insect trapping over the 7 month trial. The histogram bars for insect trapping, from left to right each month-MAFF bait bags. brown rice bait bags.
The bag analysis, spear sampling and trapping results all clearly indicate a rapidly increasing population during the first 2 months of study. The most effective traps at this stage were the refuge and pheromone traps (Fig. 10). After fumigation, all three methods of population estimation indicated that the numbers of X..flacipes were low throughout the period (Fig. 10). X.,flauipes was first detected after fumigation during the fifth month by the bait bags and did not appear in the other traps until the last month of the test. Throughout the test, the trap captures were roughly in proportion to the population changes Table
9. Mean
numbers
(i
SD)
located
MAFF
Trap
Brown
bait
bag
position
of Rhwqwrrl~rr
on the ton.
hair
0 0
< 0.05
Floor
<0.05
0.08 * 0.3
position
numbers
Top
MAFF
trial
in various
trial
I” YXIOU~
traps
0.104 * 0.3
( k SD)
located
Trap
the 7 month 4 bae stachs
WC
Side
IO. Mean
durmg around
bag
Top
Table
d~~wrr~i~tl cqurcd
sides. or on the floor
of .~y/o~w!
/hipa
captured
on the HOD. sides. or on the tloor
durmg
the 7 month
around
4 bae stacks
trapa
bait Refuge
bag 0.75 * 1.x
0.62 t
I.7
2.57 * 4 5
I .sn * b.4
Side
I.25 k 2.2
I .02 f 2.6
2.60 * 5.x
1.35 f 5.0
Floor
0.89 + 2. I
2.65 + 3.9
X6X + 7 5
1.x4 + 7.6
PItfall
2.26 * 4.9
0.4 + I .2
1.1 C 6.0
0.45 3 2.6
2 65
t
6.1
Insect traps
227
Baganalysis
0.x)
MONTHS
Fig. 9. Population estimates for Rhyzoperiha dominica * from bag analysis and insect trapping 7 month trial. The histogram bars for insect trapping, from left to right each month-brown bag, Rhyzopertha pheromone trap. *No R. dominica were obtained in spear samples.
I
Bag analysis
I
I I
4:
I I I
1
I
I I I I
I
I
I I
I I I I I
I I I . I
I
over the rice bait
Zl 01 =
+ar
sampling
I I
a I (91
5: I I.
/l-l
I
*
r-l
1
MONTHS Fig. 10. Population estimates for Xylocorisflauipes from bag analysis, spear sampling, and insect trapping over the 7 month trial. The histogram bars for insect trapping, from left to right each month-MAFF bait bag, brown rice bait bag, Rhyzopertha pheromone trap, T&o&m pheromone trap, refuge trap.
suggested by spear sampling and bag analysis. The superior performance of the bait bags after fumigation may well have been due to the presence of a concentration of the prey of X. fravipes in these bags. CONCLUSIONS It is clear from the analysis of spear sample results that, even when pests are present in large concentrations and are evenly distributed, large numbers of samples must be taken to obtain a population estimate with a reasonably high degree of precision, i.e. a sample mean with a standard error of lo-15%. The problem is particularly serious with species that have more aggregated distributions such as S. zeamais, one of the most important pests of milled rice. In the present study, routine spear sampling involved taking 50 monthly samples from each of 4 stacks. In an operational store with many more or much larger stacks, the number of spear samples needed to obtain estimates of infestations with a reasonable degree of precision is likely to be difficult to organise, very time consuming and laborious. The separation of insects from the rice samples obtained presents a further problem. The various insect traps had mixed success in monitoring the pests of milled rice. Pitfall traps worked well only for T. castaneum, whilst the refuge and pheromone traps were reasonably effective for most species. Those baited with the aggregation pheromone of R. dominica were particularly attractive for this pest; in contrast, T. castaneum was not particularly attracted to traps baited with its own aggregation pheromone, due perhaps to the use of the racemic mixture. The most successful traps were the two types of bait bag, one filled with kibbled carobs, wheat and groundnuts (MAFF bait) the other with brown rice milled from local rough rice. Most species were somewhat more attracted to the MAFF bait bags, but the brown rice was apparently more attractive to S. zeanzais and unlike the MAFF bait captured R. dominica. Both baits were exceptional in enabling the detection of T. stercorea and C. piloselhw. Throughout the study, trap catches, especially those from bait bags, changed roughly in proportion to the population changes indicated by the extensive spear sampling. This suggests that the use of traps could be extended beyond qualitative assessments or an early warning of the pests present in a store to the assessment of the size of insect population, a task normally undertaken by spear sampling. It is not clear whether the results of spear sampling or trapping bore the closer correlation with the actual insect population present in the store. However, the traps certainly gave clearer results as, with few exceptions, they captured more insects than were obtained in spear samples. In practical terms, the use of only a few traps appears to offer real advantages over extensive spear sampling as (1) they can be positioned and retrieved very easily, (2) extraction of insects from traps is less time consuming, and (3) unlike spear sampling, no damage is done to sacks. Consideration of the trapping results suggests that bait bags would be the most suitable of the methods tested for monitoring beetle pests in milled rice stores. Of the two baits, brown rice would be preferred as it is more attractive to S. zeamais, most important pest of milled rice, and is more easily obtained than the ingredients of the MAFF bait. For monitoring S. zeamais, T. stercorea and C. pilosek, bait bags would be best placed on the floor; for other species, traps on the top or sides of a stack would suffice. Catches from the top or sides of stacks were generally similar and therefore under practical conditions the traps might conveniently be deployed on the floor and the sides of a stack. The next stage in the development of this trapping method is to assess the performance of the brown rice bait bag in operational milled rice stores. Such a study should establish the number of traps to be deployed for a given stack size, the frequency with which traps should be laid, and the local acceptability of this method in Indonesia. Finally, it should establish firmly the relationship between trap catch and the size of an insect population in a store. With this knowledge it should be possible to set certain trap catch thresholds that, if exceeded, would indicate the need for pest control. AcknoMfledgemenr.r_Our sincere thanks are due to BULOG for the use of its facilities and co-operation of its staff. in particular Dr M. Sidik, Ir S. Zubaidy and Mr A. Baker (Storage Management Adviser. TDRI/BULOG Project) for helping to set up this trial at Tambun. We are grateful to Dr D. R. Hall (Insect Products Section, TDRI). for the
Insect traps provision of pheromones, to Mr D. B. Pinniger (MAFF, U.K.) for providing food bait and advice and Haines (TDRI/BIOTROP) for encouragement and the loan of essential equipment. Dr Haines identified Carpophilus pilosellus Motschulsky and the British Museum (Natural History) confirmed Xylocorisflavipes Kosim and Mr Manawar willingly shouldered much routine sampling and sample analysis and Dr D. A. Biometrics Liaison Officer) gave invaluable assistance with statistical design and analysis.
229 to Dr C. P. specimens of (Reuter). Mr Preece (ODA
REFERENCES Ashman F. (1966) Inspection methods for detecting insects in stored produce. Trap. stored Prod. Inf 12, 481494. Brady E. E., Tumlinson R. G., Brownlee R. G. and Silverstein R. M. (1971) Sex stimulant and attractant in the Indian-meal moth and the almond moth. Science 171, 802-804. Burkholder W. E. (1976) Application of pheromones for manipulating insect pests of stored products. In Insecf Pheromones and their Application (Ed. by Kono T. and Ishii S.), pp. 111-l 12. Japan Plant Protection Association, Tokyo. Finch S., Skinner G. and Freeman G. H. (1973) The distribution and analysis of cabbage root fly egg populations. Ann. appl. Biol. 79, l-18. Golob P. (1978) Techniques for sampling bagged produce. In Post-Harvest Grain Loss Assessment Methods (Ed. by Harris K. L. and Lindblad C. J.), pp. 1499161. American Association of Cereal Chemists, Washington, D.C. Hodges R. J., Hall D. R., Golob P. and Meik J. (1983) Responses of Prosfephanus truncatus to components of the aggregation pheromone of Rhyzopertha dominica in the laboratory and field. Entomologia exp. appl. 34, 266272. Hoppe T. and Levinson H. Z. (1979) Befallserkennung und Populationsiiberwachung vorratsschadlicher Motten (Phycitinae) in liner Schokoladenfabrik mit Hilfe pheromonbekoderter Klebefallen. Am. Schiidlingsk. 52, 177-183. Howe R. W. (1966) Inspection of produce and premises. Trop. stored Prod. If. 12, 475479. Kirkpatrick R. L., Niffenegger D. and Yancey D. L. (1972) Detecting stored-product moths in a peanut warehouse by using light traps and larval traps. Marketing Research Report U.S. Departmem of Agriculture No. 938. Levinson H. Z. and Mori K. (1983) Chirality determines pheromone activity for flour beetles. Naturwissenschaffen 70, lO(t192. McFarlane J. A. and Warui C. (1973) A simple technique for stored products infestation surveys. Trap. srored Prod. Inf. 24, 17-24. Pinniger D. B. (1975) A bait trap technique for assessment of stored product beetle populations. Trap. srored Prod. Inf 19, 9-l 1. Pinniger D. B., Stubbs M. R. and Chambers J. (1984) The evaluation of some food attractants for the detection of Oryzaephilus surinamensis (L.) and other storage pests. Proc. 3rd Int. Wkg Conf Stored Prod. Em., Manhattan, Kans., U.S.A.. 1983, 640-650. Reichmuth C., Schmidt H.-U., Levinson A. R. and Levinson H. Z. (1980) Das jahreszeitliche Auftreten von Speichermotten (Ephestia elurella Hbn.) in Berliner Getreideschiittbodenllgern sowie der zeitentsprechende Einsatz von Beklmpfungsmassnahmen. 2. angew. Em. 89, 104-1 Il. Ross G. J. S. (1980) MLP: Maximum Likelihood Program. Manual, Rothamsted Experimental Station. Strong R. G. (1970) Distribution and relative abundance of stored-product insects in California. A method of obtaining sample populations. J. econ. Em. 63, 591-596. Suzuki T. (1980) 4,8_Dimethyldecanal: the aggregation pheromone of the flour beetles, Tribolium castaneum and T. confusum (Coleoptera: Tenebrionidae). Agric. biol. Chem. 44, 25 19-2520. Suzuki T. (1981) Identification of the aggregation pheromone of flour beetles Tribolium castaneum and T. confusum (Coleoptera: Tenebrionidae). Agric. biol. Chem. 45, 1357-1363. Suzuki T. and Mori K. (1983) (4R, 8R)-(-)-4,8_Dimethyldecanal: the natural aggregation pheromone of the red flour beetle, Tribolium caslaneum (Coleoptera: Tenebrionidae). Appl. em. Zool. 18, 134136. Williams H. J., Silverstein R. M.. Burkholder W. E. and Korramshahi A. (1981) Dominicalure 1 and 2: components of aggregation pheromone from male lesser grain borer Rhyzopertha dominica (F.) (Coleoptera: Bostrichidae). J. them. Eeol. 7, 759978 I.
INSECT TRAPS MANAGEMENT
0022s474X;85 $3.00+O.OO Pergamon PressLtd
TESTED AS AN AID TO PEST IN MILLED RICE STORES
R. J. HODGES*, H. HALID?, D. P. REES*, J. MEIK* and J. SARJONO~ *Storage Department, Tropical Development and Research Institute, London Road, Slough SL3 7HL. Berkshire, U.K. and tBadan Urusan Logistik (BULOG). Jl. Gatot Subroto 49, P.O. Box 2345, Jakarta, Indonesia (Received 25 June 1985) Abstract-Various insect traps were tested in a milled rice store, in Indonesia, with a view to developing an insect trapping method that would enable estimates of insect populations to be obtained reliably and easily. These estimates might then be used to predict the optimum timing for pest control measures. The trial was conducted over a 7 month period in a store containing 4 bag stacks of polished rice. Trap catches were compared with population estimates obtained by sifting the contents of bags selected from all regions of the stacks and by very extensive, monthly spear sampling of outer bags. The insects observed to occur most frequently in the store were Sitophilus zeamais, Ahasverus advena, Tribolium castaneum, Oryzaephilus surinamensis, Typhaea stercorea, Carpophilus pilosellus and Xylocorisjlavipes. The precision of the spear sampling method for these species was estimated; large numbers of samples (200+) were usually required to obtain population estimates with a reasonably high degree of precision. The insect traps indicated population changes that were roughly in proportion to those indicated by spear sampling. The most useful of the traps tested was a bait bag containing brown rice milled from local rough rice. For monitoring insects in milled rice stores this trap would have several advantages over extensive spear sampling-it is positioned and retrieved more easily, the extraction of insects from it is very simple and, unlike spear sampling, it does not damage sacks. Further research is required to test traps in operational stores, particularly to establish the relationship between trap catches and the actual insect population so that trap catch thresholds may be set. Control techniques could then be applied when trap thresholds are exceeded, avoiding unnecessary treatments and optimising control.
INTRODUCTION
Insect infestation of durable, stored products may cause serious nutritional and financial losses. In order to determine how much the produce is at risk, it is important to be able to assess objectively the size and distribution of infesting insect populations. This knowledge should permit the correct timing of pest control measures so that they are applied neither too early nor too late. However, quantitative assessments are difficult to achieve; as Howe (1966) noted, there are “two difficulties, that of detecting insects . . . and that of placing an accurate numerical estimate on data subject to such an uneven distribution”. Monitoring insects in stores with traps has, for the most part, been restricted to qualitative assessments or an early warning of the insects present. Most of the common monitoring techniques were described by Ashman (1966) although important recent developments include pheromone traps (Brady et al., 1971; Burkholder, 1976) and various bags containing food baits (Strong, 1970; McFarlane and Warui, 1973; Pinniger, 1975; Pinniger et al., 1984). Quantitative determinations of insect populations in stores are almost invariably made using spear sampling, which is likely to give reliable results only when the sampling is so extensive as to require numbers of samples that may well be impractical in operational stores. For pest management purposes, quantitative determination using traps has been reported only for moths, with either light traps (Kirkpatrick et al., 1972) or sticky traps baited with synthetic sex pheromones (Hoppe and Levinson, 1979; Reichmuth et al., 1980). The purpose of the present study was to identify an insect trapping technique likely to give reliable quantitative data on which pest management decisions in milled rice stores can be made. A 7 month trial was undertaken to test several different types of trap in a bagged rice store in Indonesia. Estimates of the insect populations were made at intervals during the study by breaking down stacks and sifting the contents of bags, selected from all regions of the stacks, and by very extensive spear sampling of outer bags. These estimates were compared with the catches of various traps to determine how well the traps performed. 215
216
R. J.
MATERIALS
HODGES
AND
el
al.
METHODS
General
The test was performed over a period of 7 months at Tambun (West Java) in a store dedicated exclusively to this study. The store was a small open-eaved godown with concrete floor and corrugated iron walls and roof. It had no windows, stood 7 m up to the eaves and covered an area of 290 m’. Four bag stacks (Fig. 1) of polished rice were built in the store using 100 kg bags. Each of the four stacks (A-D) consisted of about 600 bags (60 tonnes) of rice in 13 layers. All bags were coded with coloured tags so that, if moved, they could be replaced in the same position. The tags on the outer bags of each stack, up to the 7th layer and also those on top of the stack, were numbered. This numbering enabled bags to be selected at random for spear sampling. The store was kept closed and undisturbed between sampling intervals. Insect numbers increased rapidly from the start of the test. In order to avoid excessive losses it became necessary to fumigate the rice. No attempt was made to control insects in the fabric of the store. At the end of week 8, the test was suspended for a total of 4 weeks. Two stacks were broken down and insect numbers assessed (see below), then rebuilt for the fumigation, which was performed for 1 week under gas-tight sheets with two Phostoxin tablets/tonne. One week later the sheets were removed and the test was resumed. At the start of the test the moisture content of rice samples, taken from 2 bags at each side of each stack, was determined using an Iseki-Rika resistance type meter. The mean (+ SD) moisture content was 12.62 k 0.42%; the moisture content of samples taken from the same bags at the end of the trial had risen to 13.70 +_0.16%. A thermohygrograph placed at the centre of the store, for the duration of the test, recorded a regular night/day temperature fluctuation of approx. 25-33°C. Bag analysis
When the bag stacks were built at the start of the trial, samples of 5 kg were taken from 10% of the bags going to each stack and sifted to give information on insect numbers. The bags subjected to this analysis were clearly marked and allocated at the rate of 4-5 to each layer of each stack and were distributed evenly between the outer, middle and inner regions of each layer. To record population changes with time, the examination was repeated with the same bags in stacks A and C at 8 weeks after the start of the test, the stacks being rebuilt just before fumigation. Immediately after fumigation the stacks were assumed to be free of insects. A further population estimate was made after 7 months, at the end of the test, with stacks B and D.
Stack A
I 1-4.9-12 trop positions on top of stack on &or c+rs3
Fig. I. Location shown
trap positionson
side of stock
of bag stacks (A-D) and trap positions in the experimental store. The trap positions for stack B were repeated, with the same orientation, for the other 3 stacks.
Insect traps
217
The examination of bags for insects was performed as follows: (1) In order to obtain a large representative sample from each 100 kg bag, the contents of each were passed through a Produce Flow Sampler (PFS) (Golob, 1978) set to extract a sample of about 5 kg. The residue from the sampler passed into an empty hessian bag. (2) The 5 kg sample was passed through a TPI Sack Sieve (Golob, 1978) with sieve apertures of 2.0 mm. This removed most of the insects, which were then identified and counted. (3) Both the insects and the original rice sample from the PFS were returned to the 100 kg sack from which they were extracted. The sack was sewn up. @ear sampling
At the end of each 4-week period, spear samples of 130-16Og of rice were taken from 50 randomly selected bags from each stack. The sampling spears employed were of the type used by BULOG* and were straight cylinders about 45 cm in length with an i.d. of I .5 cm. The numbers and identity of the insects in each sample were recorded. The precision with which the monthly spear sampling results estimated the population of each insect species present in the store was determined by estimating the number of samples required to give a standard error amounting to 10 or 15% of the sample mean. These estimates were made only for those months in which there were sufficient numbers of a particular species for a useful analysis. The first stage in the analysis of each set of monthly sampling results, pooled from all 4 stacks, was to fit a negative binomial distribution by the Maximum Likelihood Programme (MLP) (Ross, 1980). Chi-squared values for goodness of fit showed that discrepancies between the observed and expected values were significant (P < 0.05) for only 3 data sets out of 28, namely for Oryzaephilus surinamensis (L.) during the first month, Xylocoris JEavipes (Reuter) during the second and Carpophilus pifosellus Motschulsky during the fifth month. Mostly, negative binomial distributions fitted the data very well. Using values obtained from the fitted distributions, the sampling precisions were determined by the method described by Finch et al. (1975), where the number of samples required (ns) to achieve a mean with standard error of loop% is given by
where K is the dispersion parameter of the fitted negative binomial distribution and A4 its mean. The value of l/K has also been used here as an index for comparing the degree of dispersion, within the store, of the various insects. High values of l/K indicate low dispersion, i.e. aggregation. Refuge traps
These consisted of a strip of single layer corrugated cardboard (36 x 9 cm) folded into to give a 9 cm square (Burkholder, 1976). In order that insects should die on entering the corrugated inner layer was sprayed with a wettable powder formulation of (pirimiphos-methyl) at the rate of 1 g of active ingredient/m3. During the study there obvious repellency effects due to this treatment.
4 layers the trap Actellic were no
Pheromone traps
Each of these consisted of a refuge trap, as described above, with a plastic pheromone capsule (4 x 0.5 cm) at the centre. The pheromones used were either “Dominicalure l”, an aggregation pheromone of Rhyzopertha dominica (Fabricius) (Williams et al., 1981), prepared as described in Hodges et al. (1983) or the aggregation pheromone of Tribolium castuneum (Herbst) (Suzuki, 1981). The latter, 4,8_dimethyIdecanal, was prepared as a racemic mixture of isomers by a 7-step synthesis from 3-methylglutaric acid (Fig. 2). All the steps in the preparation were straightforward to carry out and gave products which were purified by simple distillation without the need for chromatography. Analysis of the product by capillary gas chromatography showed a single sharp peak with less than 2.5% of any single impurity (25 x 0.32 m i.d. fused silica capillary column coated *Badan
Urusan
Logistik
= National
Logistics
Agency.
218
R. J. HODGES~1 al
Fig. 2. Synthesis of 4,8-dimethyldecanal. Reagents: (i) BIH,: THF; acetic anhydride-pyridine; (ii) HBr-acetic acid; (iii) 2-methylbutylmagnesium bromide-Li&uCl,-THF; (iv) KCN-I8-Crown-bCH,CN; (v) KOH-EtOH-H20: (iv) B2H,,: THF; (vii) pyridinium chlorochromate-CH,C&.
CP Sil 5CB, helium carrier gas 0.5 kg/cm’, splitless injection at 55°C for 2 min, and then programmed at 4”C/min). The mass spectrum was identical with that reported by Suzuki (1980, 1981). The 4R, 8R isomer of 4,8-dimethyldecanal has been shown to be the most active isomer in electroantennogram and bioassay tests against T. castaneum and to be equal in activity to the natural pheromone (Suzuki and Mori, 1983; Levinson and Mori, 1983). The mixture of all 4 isomers was shown to be between T_:and h as active as the natural pheromone (Suzuki, 1981). The pheromone capsules were loaded with 1 mg of either pheromone. A fresh pheromone capsule was used each week of the study. with
Bait bag traps
These consisted of a plastic mesh (Netlon Limited, Blackburn, U.K.) envelope (8 x 16 cm). The mesh had twenty 2.0 mm apertures/cm2. The envelope was filled with approx. 60 g of either a bait consisting of equal parts of wheat, peanuts and kibbled carobs (Pinniger, 1975) (=MAFF Bait Bag) or brown rice milled from local rough rice (gabah). It was then closed with staples. The traps were disinfested after use by freezing for 1 week. The food in the traps was changed after 2 weeks use. Pitfall traps
These consisted of a 5 x 2.5 cm glass tube. the outer side of which was covered with filter paper. The paper enabled beetles to climb the outside of the tube and, as it protruded over the mouth of the tube, beetles reaching the top could fall in. The smooth inner surface of the tube prevented the escape of those beetles unable to climb glass. The traps described above were located in four positions on top of each stack, on the sides of each stack and, except for pitfall traps (which were easily knocked over) in four positions on the floor (Fig. 1). When traps were placed in the side of stacks they were pushed into the crevice between bags and when on the floor they were located almost in contact with the wooden pallets at the base of each stack. On the floor and on top of stacks the traps were lying with their upper surfaces exposed. Only one of the four types of trap was located on a stack at any one time and traps were changed at weekly intervals. Each of the four traps was deployed on a different stack each week for 4 weeks, giving a convenient 4 x 4 latin square design. A fresh square was used for each month of the trial. Bait bags and pheromone traps both existed in two forms; both forms were used on the same stack in equal numbers, occupying all odd-numbered or all even-numbered trap positions (Fig. 1) alternately. RESULTS General
A full list of the insects observed in the store during the study is given in Table 1. Less than half of these species occurred frequently enough to be given detailed consideration. The experimental results for these species, with the exception of the Psocoptera which were not counted, are presented in Tables 3-10 and Figs 3-10. Tables 3-10 give the mean catch per trap for each
Insect
traps
219
Table I. Insect species observed in the experimental store during the 7 month trial, September 1983 to March 1984 Coleoptera Anthicidae Anthicus sp. Bostrichidae Rhy:opertha dominicu (F.) Cucujidae Cr_vptolestes,ferrugineus (Stephens) Cryptokstes pusi/lus (Schenherr) Curculionidae Sitophilus xwnai.s Motschulsky Mycetophagidae Typhaea .stercorea (L.) Nitiduiidae Carpophilus pilosrilus Motschulsky Silvanidae Ahasoerus adwna (Walti) Oryraephilus surinamensis (L.) Tenebrionidae Tribolium castaneum (Herbst) Lathe&us orwae Waterhouse Alphitobius diaperinus (Panzer) Palorus ratxburgii (Wissmann) Palorus genalis (Blair) Trogossitidae Tenebroides mauritanicus L. Lepidoptera Pyralidae Phycitinae Ephestia cautella (Walker) Plodia interpunctella (Hiibner) Galleriinae Corcyra cephalonica (Stainton) Hemiptera Anthocoridae Xylocoris flauipes (Reuter) Psocoptera Liposcehdae Liposcelis entomophilus (Enderlein)
species, over the whole 7 month trial, at each of the three trap positions, i.e. the top or sides of a stack or on the floor. Figures 3-10 show, for each species, the mean monthly trap catch, calculated excluding those trap positions that consistently gave poorer results, the mean numbers from the 200 spear samples per month and the insect population as estimated by bag analysis. The shapes of the curves drawn between points on the bag analysis graphs are based on the spear sampling results. However, as spear samples could be taken only from outer bags, the shape of these curves must be regarded as largely speculative. Spear sampling
The monthly spear sampling results are shown in Table 2. For the species Ahasverus advena (Waltl), T. castaneum, 0. surinamensis and X.Javipes, the values of l/K were small, i.e. the insects were fairly evenly distributed in the store and the use of a 200 sample size would seem to have been adequate for estimating their populations during most of the test since this number of samples would give a mean value for the population with a standard error of within l&15%. Over much of the study, the mean numbers of Sitophilus zeamais Motschulsky were comparable with at least those of T. castaneum; however, its distribution was considerably more aggregated. This was shown by the values of l/K which were as much as three times as great as the values for T, castaneum. During the first and second months of the trial, the 5’. zeamais population was sampled with a precision of about 15%. After fumigation, the number of samples taken was clearly inadequate for a reasonable degree of sampling precision. This was also found with C. pilosellus and Typhaea stercorea (L.) (Table 2). Insect trapping Sitophilus zeamais. Traps placed on the floor of the store gave somewhat greater catches than elsewhere (Table 3). During the first 2 months, captures by all the types of trap increased roughly
I.10 +0.10
I .99 2 0.20
T. cm~nneunr
A. odwna
poaipes
-Insufficient
x.
C. pilosdus
numbers
244
-
-
193
I79
213
540
10%
for useful analysis.
I.17 kO.13
-
0.68 * 0.08
0. surinomen.sis
T. ,s,ercoreo
1.11+0.19
species Mean+ SE
I
107
-
-
85
79
120
240
15%
6.04 kO.37
1.69~0.16
0.86 + 0.09
77
I80
236
186
41 I
10%
Top Side Floor
Trap position
MAFF bag 1.03 f I.15 f I .77 f 3.1 I.0 4.2
bait
0.60
-
-
I.21
I .20
0.84
3.47
UK
0.49 + 0.10
0.46+0.1?
I.01 kO.16
I.21 ro.13
_
Mean + SE
5
807
1215
505
238
10%
degree of population IO or 15%
387
539
224
I05
15%
aggregation
-
6.60
10.00
4.06
1.56
-
~
l/K
0.42 + I .5 1.33 f 3.0 3.0 f 6.6
Brown rice bait bag
Trap
<0.05 0.23 f 0.8 I .65 + 5.2
Rhymperrha pheromone
0.08 k 0.5 0.17 +0.6 0.8 + 2.0
Tribolium pheromone
type Refuge 0.135+0.6 0.22 * 0.7 I .25 + 3.9
586
875
422
I32
223
470
1268
6 ~ 10%
0 <0.05
Pitfall
260
385
I86
58
99
208
563
3.30
6.80
3.1 I
I.19
1.56
0.30 + 0.06
0.33 & 0.13
0.56 i 0.1 I
3.93 * 0.44
0.65 i 0.09
0.97+0.12
I .99 * 0.32
I I.23 3.57
Mean k SE
881
24X
803
233
357
315
484
10%
1
353
104
I59
140
215
15%
391
5.31
21.27
6.28
2.08
2.04
2.12
4.34
I/K
precision
IO65
to gwe a sampling
I/K
of spear sample\
..~ 15%
number
trial in various
0.39 k 0.06
0.52 * 0. I I
0.99*0.15
7.43 f 0.62
1.49_+0.16
0.88 ? 0.14
0.69+0.18
Mean + SE
(l/K) and the required
of adult Silophilus xamais captured during the 7 month on the top, sides, or on the floor around 4 bag stacks
34
79
104
82
I81
15%
Table 3. Mean numbers (*SD) traps located
0.29
-
-
I .43
0.88
0.97 f 0.09
I.57 + 0.22
4.54
1.26
Mean + &
2
spear sample<. the observed
VK
(k SE) of insects from 200 monthly
s. xaml7i.i
Insect
Months:
Table 2. Mean numbers
of
221
Insect traps
I I
I
I
I I
Spear
I I
I I
lropping
I
n 0
1
I
I
I
2
sampling
3
5
6
7
M&S
Fig. 3. Population estimates for adult Sitophilus zeamais from bag analysis, spear sampling, and insect trapping over the 7 month trial. The histogram bars for insect trapping, from left to right each month-MAFF bait bags, brown rice bait bags, Rhyzopertha pheromone trap, Tribolium pheromone trap, refuge trap.
in proportion to the population increases suggested by spear sampling and bag analysis (Fig. 3). After fumigation, only the bait bag results maintained a constant proportional relationship with the spear sample results (Fig. 3) although during this period the number of spear samples taken was generally inadequate to give a high degree of precision (Table 2). Except in the fifth month, the bait bags filled with brown rice trapped consistently more S. zeamais than those with the MAFF bait (Fig. 3). After fumigation both the insect traps and spear sample results suggested a greater population of S. zeamais than would have been expected from the bag analysis results. In view of the aggregated distribution of S. zeamais demonstrated by spear sampling (Table 2), it would seem likely that during the bag analysis a rather low proportion of infested bags were sifted; this would give rise to a low population estimate. Oryzaephilus surinamensis. Trap catches from the top and sides of the stacks and the floor gave similar results (Table 4) and all traps were fairly effective in monitoring the pest (Fig. 4). After fumigation, the MAFF bait bags proved to be the most effective traps and captured some beetles
Table 4. Mean numbers (I SD) of adult Oryraephilus surinamensis captured during the 7 month various traps located on the top, sides, or on the floor around 4 bag stacks
trial in
Trap type Trap
position
TW Side Fl00r
MAFF
bait
Brown
rice
bag
bait bag
0.46 2 0.9 0.7 + 1.2 0.6 + I.2
0.31 k 0.6 0.53 i_ 1.4 0.48 * I .2
Rhyzoperlha pheromone < 0.05 0.29 & 0.9 0.72 + I .9
Tribolium pheromone
Refuge
Pitfall
0.16kO.5 0.25 2 0.9 0.48 + 0.9
0.23 rt 0.6 0.09 i 0.4 0.47 & 2.0
to.05 co.05
222
R. J. HODGESet al.
1.1
p 0.9 e > 0.6 ? SO.3 z 0 1
2
3
4
5
6
7
MONTHS
Fig. 4. Population estimates for Uryzaephilus surinumensis from bag analysis, spear sampling, and insect trapping over the 7 month trial. The histogram bars for insect trapping, from left to right each month-MAFF bait bag, brown rice bait bag, Rhyzoperfha pheromone trap, Tribolium pheromone trap, refuge trap.
during the fifth month when other traps failed to catch any. Catches from all traps were roughly in proportion to the population changes indicated by spear sampling and bag analysis (Fig. 4). Tribolium castaneum. The mean trap catch data in Table 5 show clearly that the pitfall traps did better on top of the stacks, the bait bag and refuge traps did better on the tops and sides of stacks, and the remaining traps did about equally well in all three positions. Bag analysis suggested that during the first 2 months there was a slight increase in population (Fig. 5). In contrast, the spear sampling results suggested a decrease of about 23%. The trapping results did not resolve this confusion as the bait bags and pitfall traps indicated a slight decrease in population while the pheromone and refuge traps suggested a slight increase (Fig. 5). After fumigation, the results were easier to understand. The population changes indicated by spear sampling were roughly in proportion to those suggested by the trap captures, particularly those from the bait bags and pitfall traps (Fig. 5). It was disappointing that the specific Triboiium pheromone traps captured so few beetles.
Table 5. Mean numbers (+ SD) of adult Tribolium cusmmnn captured during the 7 month trial in various traps located on the top, sides, or on the floor around 4 bag stacks Trap type Trap
position Top Side Fl00r
MAFF
bait
Brown rice
Rhy:operrha
bag
bait bag
pheromone
29.27 + 33.9 26. I4 + 32. I s.25 + 8.2
12.62 k 12.1 13.45 + 13.3 6.20 + 5.9
2.45 k 2.2 3.45 ? 3.3 2.33 + 2.0
Tribolium
pheromone 4.69 + 3.4 4.96 f 3.9 4.54 f 3.3
Refuge 3.5 * 3.8 3.25 + 4.3 1.8 + 2.3
Pitfall 17.57 * 19.0 8.83 f 7.5 -
Insect traps
223
Table 6. Mean numbers
Ahasverus advenu. Trap catches on the floor and the top and sides of the stacks were all of similar size (Table 6). All traps were effective in catching this beetle although the bait bags were especially good after fumigation (Fig. 6). At the start of the test the A. adwnu population was relatively high but all traps and the spear sample results subsequently indicated a decline in the population size. The extent of the decline was so great that at the bag analysis just before fumigation no A. advena were detected (Fig. 6). The MAFF bait bag gave an early warning of this pest after fumigation and indicated a progressive population increase from the fifth month to the end of the trial. The other traps, except the brown rice bait bags, indicated a progressive increase from the sixth month (Fig. 6). With the brown rice bait bags. the population dropped slightly between the sixth and seventh months. Spear sampling showed a greater drop in the same period, at a time when the precision of spear sampling was high (Table 2). One explanation for the difference between the spear sampling results and trap catches. except those for the brown rice bait bags, could be that during the seventh month A. advena adults were distributing themselves from the stacks. This would lead to higher trap catches but
MONTHS
Fig. 5. Population estimates for Triholium ~u~tmaun from bag analysis, spear sampling, and insect trapping over the 7 month trial. The histogram bars for insect trapping, from left to right each monthMAFF bait bag, brown rice bait bag. R/r~zoper/h pheromone trap. Tribolium pheromone trap, refuge trap, pitfall trap.
R. J. HODGES el al.
224
MONTHS
Fig. 6. Population estimates for adult Ahasoerus adwna from bag analysis, spear sampling, and insect trapping over the 7 month trial. The histogram bars for insect trapping, from left to right each month-MAFF bait bag, brown rice bait bag, Rhyzopertha pheromone trap, Tribolium pheromone trap, refuge trap.
lower spear sampling results. This explanation is consistent with the relatively low bag analysis result recorded at the end of the trial, which was smaller than might have been expected from the trap and spear sample results. Typhaea stercorea and Carpophilus pilosellus. Both species were encountered only rarely before fumigation. After fumigation, they became very much more numerous (Figs 7 and 8) possibly due to the rise in ambient humidity that came with the onset of the main rainy period during the fourth month of the trial. They entered traps most frequently when these were placed on the floor (Tables 7 and 8). Only the bait bags captured any appreciable numbers of T. srercorea or C. pilosellus. For both species, the proportional changes in population suggested by trap catches coincided with those indicated by spear sampling (Figs 7 and 8) despite the generally low precision with which the spear samples estimated the populations (Table 2).
Table 7. Mean numbers (k SD) of adult Typhaea stwmrea captured during the 7 month trial in various traps located on the too. sides. or on the floor around 4 bae stacks Trap type Trap position
MAFF bait bag
Brown we bait bag
Rhyroperlha pheromone
Top Side Floor
6.4 +_7.2 9.4* 13.8 23.34 + 69.2
1.37 * 3.8 0.156+0.45 9.45 + 16.1
0 co.05 < 0.05
Tribolium pheromone 0 CO.05 CO.05
Refuge
Pafall
0 <0.05 co.05
< 0.05 <0.05 -
Insect
225
traps
-_u_
Trapping
MONTHS Fig. 7. Population estimates trapping over the 7 month
for adult 7’yphuea srerc~reu from bag analysis, spear sampling, and insect trial. The histogram bars for insect trapping, from left to right each month-MAFF bait bag, brown rice bait bag.
The numbers encountered in the spear samples and bag analysis were much smaller than the numbers of both species extracted from the traps (Figs 7 and 8). It can only be assumed that the populations of these beetles did not penetrate the bags and were mostly localised on bag surfaces or on store structures. Rhyzopertha dominica. R. dominica was present in the store at very low population density. It was captured only in the specific Rhyzopertha pheromone baited trap and in the brown rice bait bags. In both of these types of trap, the catches were fairly evenly distributed between the three trap positions (Table 9). Owing to the very low population present in the store, the trap catches were very variable (Fig. 9). No individuals of this species were detected in spear samples and only during the first 2 months was the beetle found during bag analysis. XylocorisJEavipes. X.Jlavipes is a predator of stored products pests. Its presence in traps in large numbers would indicate that a significant pest population exists in a store. X.javipes was captured frequently in the traps (Fig. 10) and there was no clear distinction between trap catches from the three trap positions (Table 10).
Table
8. Mean
(*SD) of adult Carpophilus pilosellus captured during the 7 month trial in various traps located on the top, sides, or on the floor around 4 bag stacks
numbers
Trap type Trap position -fop Side
Floor
_~.
MAW bait bag
Brown rice bait bag
Rhyzopertha pheromone
Tribolium pheromone
Refuge
Pitfall
5.43 + 12.7 13.96 k 29.0 48.03 + 57.7
3.0 + 6.7 4.03 * 8.9 48.51 f 67.3
<0.05 0 <0.05
<0.05 <0.05 0.21 f 0.6
0 < 0.05 <0.05
0 < 0.05
226
MONTHS Fig. 8. Population estimates for adult Curpop/~ilu.s prhe/lrrs from bag analysis. spear sampling, and insect trapping over the 7 month trial. The histogram bars for insect trapping, from left to right each month-MAFF bait bags. brown rice bait bags.
The bag analysis, spear sampling and trapping results all clearly indicate a rapidly increasing population during the first 2 months of study. The most effective traps at this stage were the refuge and pheromone traps (Fig. 10). After fumigation, all three methods of population estimation indicated that the numbers of X..flacipes were low throughout the period (Fig. 10). X.,flauipes was first detected after fumigation during the fifth month by the bait bags and did not appear in the other traps until the last month of the test. Throughout the test, the trap captures were roughly in proportion to the population changes Table
9. Mean
numbers
(i
SD)
located
MAFF
Trap
Brown
bait
bag
position
of Rhwqwrrl~rr
on the ton.
hair
0 0
< 0.05
Floor
<0.05
0.08 * 0.3
position
numbers
Top
MAFF
trial
in various
trial
I” YXIOU~
traps
0.104 * 0.3
( k SD)
located
Trap
the 7 month 4 bae stachs
WC
Side
IO. Mean
durmg around
bag
Top
Table
d~~wrr~i~tl cqurcd
sides. or on the floor
of .~y/o~w!
/hipa
captured
on the HOD. sides. or on the tloor
durmg
the 7 month
around
4 bae stacks
trapa
bait Refuge
bag 0.75 * 1.x
0.62 t
I.7
2.57 * 4 5
I .sn * b.4
Side
I.25 k 2.2
I .02 f 2.6
2.60 * 5.x
1.35 f 5.0
Floor
0.89 + 2. I
2.65 + 3.9
X6X + 7 5
1.x4 + 7.6
PItfall
2.26 * 4.9
0.4 + I .2
1.1 C 6.0
0.45 3 2.6
2 65
t
6.1
Insect traps
227
Baganalysis
0.x)
MONTHS
Fig. 9. Population estimates for Rhyzoperiha dominica * from bag analysis and insect trapping 7 month trial. The histogram bars for insect trapping, from left to right each month-brown bag, Rhyzopertha pheromone trap. *No R. dominica were obtained in spear samples.
I
Bag analysis
I
I I
4:
I I I
1
I
I I I I
I
I
I I
I I I I I
I I I . I
I
over the rice bait
Zl 01 =
+ar
sampling
I I
a I (91
5: I I.
/l-l
I
*
r-l
1
MONTHS Fig. 10. Population estimates for Xylocorisflauipes from bag analysis, spear sampling, and insect trapping over the 7 month trial. The histogram bars for insect trapping, from left to right each month-MAFF bait bag, brown rice bait bag, Rhyzopertha pheromone trap, T&o&m pheromone trap, refuge trap.
suggested by spear sampling and bag analysis. The superior performance of the bait bags after fumigation may well have been due to the presence of a concentration of the prey of X. fravipes in these bags. CONCLUSIONS It is clear from the analysis of spear sample results that, even when pests are present in large concentrations and are evenly distributed, large numbers of samples must be taken to obtain a population estimate with a reasonably high degree of precision, i.e. a sample mean with a standard error of lo-15%. The problem is particularly serious with species that have more aggregated distributions such as S. zeamais, one of the most important pests of milled rice. In the present study, routine spear sampling involved taking 50 monthly samples from each of 4 stacks. In an operational store with many more or much larger stacks, the number of spear samples needed to obtain estimates of infestations with a reasonable degree of precision is likely to be difficult to organise, very time consuming and laborious. The separation of insects from the rice samples obtained presents a further problem. The various insect traps had mixed success in monitoring the pests of milled rice. Pitfall traps worked well only for T. castaneum, whilst the refuge and pheromone traps were reasonably effective for most species. Those baited with the aggregation pheromone of R. dominica were particularly attractive for this pest; in contrast, T. castaneum was not particularly attracted to traps baited with its own aggregation pheromone, due perhaps to the use of the racemic mixture. The most successful traps were the two types of bait bag, one filled with kibbled carobs, wheat and groundnuts (MAFF bait) the other with brown rice milled from local rough rice. Most species were somewhat more attracted to the MAFF bait bags, but the brown rice was apparently more attractive to S. zeanzais and unlike the MAFF bait captured R. dominica. Both baits were exceptional in enabling the detection of T. stercorea and C. piloselhw. Throughout the study, trap catches, especially those from bait bags, changed roughly in proportion to the population changes indicated by the extensive spear sampling. This suggests that the use of traps could be extended beyond qualitative assessments or an early warning of the pests present in a store to the assessment of the size of insect population, a task normally undertaken by spear sampling. It is not clear whether the results of spear sampling or trapping bore the closer correlation with the actual insect population present in the store. However, the traps certainly gave clearer results as, with few exceptions, they captured more insects than were obtained in spear samples. In practical terms, the use of only a few traps appears to offer real advantages over extensive spear sampling as (1) they can be positioned and retrieved very easily, (2) extraction of insects from traps is less time consuming, and (3) unlike spear sampling, no damage is done to sacks. Consideration of the trapping results suggests that bait bags would be the most suitable of the methods tested for monitoring beetle pests in milled rice stores. Of the two baits, brown rice would be preferred as it is more attractive to S. zeamais, most important pest of milled rice, and is more easily obtained than the ingredients of the MAFF bait. For monitoring S. zeamais, T. stercorea and C. pilosek, bait bags would be best placed on the floor; for other species, traps on the top or sides of a stack would suffice. Catches from the top or sides of stacks were generally similar and therefore under practical conditions the traps might conveniently be deployed on the floor and the sides of a stack. The next stage in the development of this trapping method is to assess the performance of the brown rice bait bag in operational milled rice stores. Such a study should establish the number of traps to be deployed for a given stack size, the frequency with which traps should be laid, and the local acceptability of this method in Indonesia. Finally, it should establish firmly the relationship between trap catch and the size of an insect population in a store. With this knowledge it should be possible to set certain trap catch thresholds that, if exceeded, would indicate the need for pest control. AcknoMfledgemenr.r_Our sincere thanks are due to BULOG for the use of its facilities and co-operation of its staff. in particular Dr M. Sidik, Ir S. Zubaidy and Mr A. Baker (Storage Management Adviser. TDRI/BULOG Project) for helping to set up this trial at Tambun. We are grateful to Dr D. R. Hall (Insect Products Section, TDRI). for the
Insect traps provision of pheromones, to Mr D. B. Pinniger (MAFF, U.K.) for providing food bait and advice and Haines (TDRI/BIOTROP) for encouragement and the loan of essential equipment. Dr Haines identified Carpophilus pilosellus Motschulsky and the British Museum (Natural History) confirmed Xylocorisflavipes Kosim and Mr Manawar willingly shouldered much routine sampling and sample analysis and Dr D. A. Biometrics Liaison Officer) gave invaluable assistance with statistical design and analysis.
229 to Dr C. P. specimens of (Reuter). Mr Preece (ODA
REFERENCES Ashman F. (1966) Inspection methods for detecting insects in stored produce. Trap. stored Prod. Inf 12, 481494. Brady E. E., Tumlinson R. G., Brownlee R. G. and Silverstein R. M. (1971) Sex stimulant and attractant in the Indian-meal moth and the almond moth. Science 171, 802-804. Burkholder W. E. (1976) Application of pheromones for manipulating insect pests of stored products. In Insecf Pheromones and their Application (Ed. by Kono T. and Ishii S.), pp. 111-l 12. Japan Plant Protection Association, Tokyo. Finch S., Skinner G. and Freeman G. H. (1973) The distribution and analysis of cabbage root fly egg populations. Ann. appl. Biol. 79, l-18. Golob P. (1978) Techniques for sampling bagged produce. In Post-Harvest Grain Loss Assessment Methods (Ed. by Harris K. L. and Lindblad C. J.), pp. 1499161. American Association of Cereal Chemists, Washington, D.C. Hodges R. J., Hall D. R., Golob P. and Meik J. (1983) Responses of Prosfephanus truncatus to components of the aggregation pheromone of Rhyzopertha dominica in the laboratory and field. Entomologia exp. appl. 34, 266272. Hoppe T. and Levinson H. Z. (1979) Befallserkennung und Populationsiiberwachung vorratsschadlicher Motten (Phycitinae) in liner Schokoladenfabrik mit Hilfe pheromonbekoderter Klebefallen. Am. Schiidlingsk. 52, 177-183. Howe R. W. (1966) Inspection of produce and premises. Trop. stored Prod. If. 12, 475479. Kirkpatrick R. L., Niffenegger D. and Yancey D. L. (1972) Detecting stored-product moths in a peanut warehouse by using light traps and larval traps. Marketing Research Report U.S. Departmem of Agriculture No. 938. Levinson H. Z. and Mori K. (1983) Chirality determines pheromone activity for flour beetles. Naturwissenschaffen 70, lO(t192. McFarlane J. A. and Warui C. (1973) A simple technique for stored products infestation surveys. Trap. srored Prod. Inf. 24, 17-24. Pinniger D. B. (1975) A bait trap technique for assessment of stored product beetle populations. Trap. srored Prod. Inf 19, 9-l 1. Pinniger D. B., Stubbs M. R. and Chambers J. (1984) The evaluation of some food attractants for the detection of Oryzaephilus surinamensis (L.) and other storage pests. Proc. 3rd Int. Wkg Conf Stored Prod. Em., Manhattan, Kans., U.S.A.. 1983, 640-650. Reichmuth C., Schmidt H.-U., Levinson A. R. and Levinson H. Z. (1980) Das jahreszeitliche Auftreten von Speichermotten (Ephestia elurella Hbn.) in Berliner Getreideschiittbodenllgern sowie der zeitentsprechende Einsatz von Beklmpfungsmassnahmen. 2. angew. Em. 89, 104-1 Il. Ross G. J. S. (1980) MLP: Maximum Likelihood Program. Manual, Rothamsted Experimental Station. Strong R. G. (1970) Distribution and relative abundance of stored-product insects in California. A method of obtaining sample populations. J. econ. Em. 63, 591-596. Suzuki T. (1980) 4,8_Dimethyldecanal: the aggregation pheromone of the flour beetles, Tribolium castaneum and T. confusum (Coleoptera: Tenebrionidae). Agric. biol. Chem. 44, 25 19-2520. Suzuki T. (1981) Identification of the aggregation pheromone of flour beetles Tribolium castaneum and T. confusum (Coleoptera: Tenebrionidae). Agric. biol. Chem. 45, 1357-1363. Suzuki T. and Mori K. (1983) (4R, 8R)-(-)-4,8_Dimethyldecanal: the natural aggregation pheromone of the red flour beetle, Tribolium caslaneum (Coleoptera: Tenebrionidae). Appl. em. Zool. 18, 134136. Williams H. J., Silverstein R. M.. Burkholder W. E. and Korramshahi A. (1981) Dominicalure 1 and 2: components of aggregation pheromone from male lesser grain borer Rhyzopertha dominica (F.) (Coleoptera: Bostrichidae). J. them. Eeol. 7, 759978 I.