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The effects of the temperature-toxicity relationships of certain pesticides upon the population growth of Sitophilus oryzae (L.) (Coleoptera: Curculionidae)
J.srurrd Prod.Rrs.Vol.19.No. 1,
pp.
Printed in Great Britain. All rights
reserved
'S-29.1983
0022-474X/83/010025-05$03.00/0
Copyright 0 1983Pergamon Press Ltd
THE EFFECTS OF THE TEM.PERATURE-TOXICITY RELATIONSHIPS OF CERTAIN PESTICIDES UPON THE POPULATION GROWTH OF SITOPHILUS ORYZAE (L.) (COLEOPTERA: CURCULIONIDAE) B. C. LONGSTAFF
and J. M. DESMARCHELIER
CSIRO Division of Entomology, P.O. Box 1700. Canberra City. A.C.T. 2601. Australia (Receiced Abstract-An
irl jiml
form
15 July 1982)
experiment to assess the effects of temperature upon the toxicity of two pesticides
to Sitopldus
oryzae is described. The pesticides used, pirimiphos-methyl and deltamethrin. were shown to hive opposite relationships with temperature. The consequences of these relationships are discussed in relation to the population growth of S. oryzuu and, in particular. to the use of cooling in combination with low levels of pesticide as an integrated control measure for this and other pest species.
INTRODUCTION
THE RELATIONSHIPS between
the toxicity of insecticides and temperature have been extensively studied IBusvrr\ls. 1971). Such studies have practical relevance to grain protectants because the stored grain environment can be readily manipulated. Studies on the longterm effects of environmental variables on the toxicity of grain protectants can help to define the minimum amount necessary to prevent the growth of pest populations. The effects of such variables on the persistence, as distinct from the toxicity, of protectants was minimized, in the present study, by the selection of two persistent chemicals: pirimiphos-methyl and deltamethrin. Pirimiphos-methyl, an organophosphorus insecticide, and deltamethrin, ;.I pyrethroid, would be expected to show, respectively, positive and negative temperature effects upon adult mortality (BUSVINE, 1971). The aims of this study were to confirm this expectation with reference to Sitoplliltrs ory:ae (L.) and, more especially, to investigate the joint effects of grain temperature and sub-optimal levels of each pesticide on its population growth. MATERIALS
AND
METHODS
Both deltamethrin and pirimiphos-methyl were supplied as emulsifiable concentrates, with 25 and 900 g per litre a.i., respectively. The experimental design consisted of using three temperalures (21, 27 and 32.3”C) at each of which five treatments were employed: an untreated control, two levels of pirimiphos-methyl, and two levels of deltamethrin. The duration Iof the experiment was four weeks and each treatment was replicated eight times for each week. The levels of deltamethrin employed were nominally 0.05 and 0.1 mg kg-’ and it was synergised with 8 g per litre piperonyl butoxide. The levels of pirimiphos-methyl employed were 0.25 and 0.4 mg kg- ‘. For each of the treatments, Australian Standard White wheat, of the variety Olympic, was conditioned to achieve a grain m.c. of 12.5%. The pesticides were applied to 4.5 kg of wheat, at appropriate levels, by pipette at a.rate of 0.002 litres per kg. Pirimiphos-methyl was applied in an acetone solution, deltamethrin in water. The pesticide and wheat were mixed manually and then left to equilibrate for one week at 3O”C, before being remixed and used for the bioassay experiments. The treated wheat was not analysed to confirm dosage and so application must be considered as nominal. Any breakdown of the pesticides during the experimental
26
B. C. LONGSTAFF and
J. M. DESMARCHELIER
period would be negligible and would be within the range of accuracy of the analytical methods used (DESMARCHELIERet al., 1980; J. SNELSON, personal communication). Following mixing, the wheat was divided up into 45 g lots (8 replicates x 4 weeks x 3 temperatures for each treatment) and placed in glass jars with perforated screw tops. Six pairs of O-24 hr old S. oryzae were then placed in each jar and 32 jars of a given treatment were placed together in an incubator maintained at the desired temperature. The grain m.c. was maintained by means of trays of saturated sodium bromide solution. This gave an e.r.h. of 55% (SOLOMON, 1951). After 1 week, the number of live insects remaining in each jar was assessed and these were then transfered to the next set of eight jars. The used wheat was incubated until all progeny had emerged and any emergent adults were removed weekly. The procedure was repeated each week for the duration of the experiment. The data obtained are presented as the means i: SE of the eight replicates. RESULTS AND DISCUSSION Pirimiphos-methyl exhibited a consistent, positive temperature effect on adult mortality in that, for each time period and each level of exposure, mortality increased over the range 21&32.3”C (Table 1). Deltamethrin was more toxic at 21°C than at either 27 or 32.3”C, but there were no significant differences in its toxicity between the latter two temperatures (Table 1). In terms of fecundity. the situation was more complex. Fecundity has been defined in this study as the ratio of the number of female offspring emerging to the mean number of females alive during the period of exposure. assuming a sex-ratio of 1 : 1. At all temperatures, the lower application rate for pirimiphos-methyl (a nominal 0.25 mg kg- ‘) had only a minor effect upon the number of progeny produced per female whereas at the higher rate (a nominal 0.4 mg kg- ‘) there was a positive relationship hith temperature: the higher the temperature the greater the reduction in fecundity (Table 2). This reduction increased with time of exposure. Deltamethrin showed the least effect at 27”C, where the fecundity for the first week of exposure was actually greater, at the lower application rate. than that of the control cultures and there was a similar increase in fecundity in the first week at 32.3 C (Table 2). No explanation of this phenomenon is offered. In most instances. the pesticide did not greatly affect the fecundity in the first week of exposure, but reductions became more pronounced with time. The effects of these pesticides upon the demographic potential of this species may be readily seen by plotting time, (x), against I\-L?,,which is the product of the proportion of females alive at time X, (I,), and the mean number of female progeny produced in a unit
TABLEI. THE CIJMIJLATM SURVIVAL OF MATURE S. OT~XC ~XPOSFIITO PIRIMIPHOS-MLTH~I. :\\I)IXL.IAMI.THKI~ OVER A PERIOD OF 4 WEEKS. THE RESULTS ARF PRESENTED AS MAN WMLLATIW SIKWIAL (I,)2 SE Treatment Control
Deltamethrin and piperonyl butoxide (0.05 mg kg- ‘) Deltamethrin and piperonyl butoxide (0.1 mg kg-‘) Pirimiphosmethyl (0.25 mg kg ’ ) Pirimiphosmethyl (0.4 mg kg- ‘)
Weeks
Temperature (‘C)
1
2
21
1.00
I .oo
21
1.00
32.3 21 27 32.3 21 27 32.3 21 27 32.3 21 27 32.3
1.00 0.71 0.88 0.95 0.42 0.69 0.84 0.97 0.95 0.56 0.95 0.47 0.17
0.99 1.00 0.50 0.80 0.89 0.30 0.58 0.72 0.96 0.73 0.22 0.89 0.24 0.01
& + f f f * f f f + * *
0.14 0.07 0.08 0.10 0.16 0.14 0.05 0.04 0.17 0.07 0.09 0.12
3
3
1.00 * 0.02 + f + & f * i & * i k +
0.1 I 0.09 0.07 0.13 0.17 0.09 0.06 0.13 0.14 0.13 0.1 1 0.02
0.99 0.99 0.42 0.76 0.86 0.22 0.55 0.61 0.96 0.47 0.13 0.87 0.03 0.01
* * * i i i * + f i * * k f
0.02 0.02 0. I I 0.1 I 0.07 0.12 0.15 0.10 0.05 0.16 0.10 0.1’ 0.06 0.02
0.99 0.96 0.32 0.70 0.75 0. I4 0.50 0.50 0.91 0.38 0.1 I 0.77 0.01 0.0
& * * * * * * * i i
0.07 0.05 0. I2 0.09 0.13 0.09 0. I3 0. I2 0.06 0.20 i 0.1 I f 0.16 * 0.02
The Effects of Pesticides
TABLE
2. THE
AGE-SPECIFIC
FECUNDITY
upon the Population
(0,)
OF S.
oryxe.
PROGENY
Growth
THE
DATA
PER FEMALE
i
of Sitophilus
ARE
21 27 32.3 21 27 32.3 21 27 32.3 21 27 32.3 21 27 32.3
Deltamethrin and piperonyl butoxide (0.05 mg kg- r) Deitamethrin and piperonyl butoxide (0.1 ray klj_ I) Pirimiphosmethyl (0.25 mg kg- ‘) Pirimiphosmethyl (0.4 mg kg- t)
NUMBER
OF
LIVE
FEMALE
Weeks
I
(“C)
Control
MEAN
27
SE
Temperature
Treatment
THE
oryzae
3.2 9.8 3.6 2.5 16.3 9.1 2.0 7.0 4.1 6.2 9.1 4.5 2.6 6.3 2.9
z
f 1.3 + 5.3 f 2.1 2 1.2 k 2.0 k 4.6 ri_ 1.3 & 2.9 f 1.7 k 4.1 f 2.0 * 2.1 i 1.3 i 3.6 + 2.3
8.9 16.4 7.8 4.4 18.0 6.0 3.5 9.1 2.9 8.2 15.1 8.2 6.1 11.8 1.3
* + k f + f & f * f f k f f +
3 3.4 5.2 4.1 2.3 3.2 2.7 3.0 4.5 1.4 2.5 3.9 3.1 3.0 10.7 1.5
8.7 16.4 7.3 4.1 13.2 3.3 2.8 7.9 2.4 10.4 17.0 6.2 9.0 6.0 0.0
4
f f * + f * f & k * + k * +
1.3 6.6 3.4 2.2 3.8 2.5 2.1 6.5 0.9 3.3 8.1 5.5 4.4 7.2
8.7 16.1 7.1 1.9 16.9 0.3 0.8 6.7 0.7 5.1 17.1 6.4 3.9 0.0 0.0
f k * f + + k + & * * + +
1.6 4.9 3.4 3.5 5.5 0.2 1.6 5.2 0.1 2.3 6.8 5.9 1.3
of time by a female of age x,uX (Fig. 1). BIRCH (1948) considered the product of l,m,, where m, is the number of female eggs laid by a female of age .Y in a unit of time. He modified I, to include the effect of immature mortality, whereas it is implicit in the term v,. At the coolest temperature (21”(Z), the deltamethrin treatments showed very low, flat response curves over time. In the populations exposed to pirimiphos-methyl, the values initially rose, as did that for the control populations, but then declined sharply at the end of the experimental period. Because, at 21°C the first 4 weeks of reproductive life contributed almost 60% of the population growth rate (BIRCH, 1948), the major reductions brought about by the low levels of deltamethrin would severely inhibit population growth at this temperature. At the warmest temperature (32.3”(Z), pirimiphos-methyl was more effective than deltamethrin during the first two weeks, but all treatments converged to almost lOOO,/,control by the end of the experimental period. A summation of IXv, over rate (BIRCH, the experimental period provides an estimate of &, the net reproductive
Id
2 2
18
le.
16.
14
14
12
-
10
_
42-
IC)
12.
.-/s_. lo
0’ ,‘.\
a6-
ibi
I
18
.
/
I’
.’
,’
‘\ \ \ \o \
\
/ I/ /I .q
\ .
o-o--o .---•-__
0 1
a-
2
\ \. s---._
3
4
6-
l_--.. -. 0.
4-
‘\.
l --_. ‘\
2t o
*
2-
\ \ \.
12
-=--_._ 40 3
x
4-
“Qx_ l I 1
-_
”
‘;=zx, \ --*a
-*=--,_-_)_
2
3
4
(weeks)
FIG. 1. The effect of pesticide treatment on demographic performance as indicated by the product of cohort survival and age-specific fecundity (I,v,) (A-A) Control; (O---O) 0.25 mg kgg’ pirimiphos-methyl; (B-m) 0.4 mg kg- ’ pirimiphos-methyl; (C-O) 0.05 mg kg- ’ deltamethrin; (t-0) 0.1 mg kg-’ deltamethrin (a) 21°C. (b) 27”C, (c) 32.3’C.
B. C. LONGSTAFF and J. M. DEWARCHELIER TABLE
i. THE
NET
REPRODUCTIVE
Temperature (-C)
Control
RO
‘I
21 32.3
TO
DELTAMETHRIN
AND
Pirimiphos-methyl Deltamethrin 0.05 mg kg- ' 0.1mg kg ’ 0.25 mg kg- ’ 0.1mg kg- ’
19.5
O0of control RO "o of control R, ","of control
EXPOSED
RATE OF S. oryxw PIRIMIPHOS-METHYL
58.7
6.4 21.3 50.8
2.5 8.5
x.4 96.3
18.8 63.7
76.4
86.5 16.7
11.9 30.5 7.5
34.0 57.9 5.8
6.0 10.2 0.5
63.1
28.3
72.0
2.0
1948). These estimates and their relationship to the corresponding control values are given in Table 3. The data presented above may be used to derive an estimate of the intrinsic rate of increase, r, which describes exponential growth. Thus, :V, = NOerr where N, is the initial population size and N, the population at time t. This is readily done using a Leslie-type matrix model (LESLIE, 1945; USHER, 1972). This model is a set of difference equations that include age-specific mortality and reproductive rates. Thus. we have a matrix. M: 0
0
0
0
v,
v,
v,
v4
.
lo...
0 .
Ol...
.
.Ol.. M=
.
1..
.
.
.
.
.
.
P 1.2
.
.
.
.
.
0
P 2.3 .
P,,,
0
where Vi is the number of female progeny per female adult of age i: Pi,;+ 1 is the rate of survival from age i to i + I. In the example above there are 4 immature age-classes, each of 1 week duration. This is the situation at 27’C. but at ?I and 32.3~C the immature periods are protracted to eight and five weeks respectively. Appropriate changes must be made to the matrix when considering these temperatures. Immature survival is given as unity in each class because the mortality is implicit in the values of Vi. The calculation of the dominant eigenvalue of such a matrix provides one with an estimate of the finite rate of increase (i) (BIRCH, 1948; LESLIE, 1945), the natural logarithm of which is r. The latter is the intrinsic rate of increase per unit time and a value of zero indicates that the population size does not change. Estimates of r were calculated and are shown in Table 4. From this analysis it is clear that, at 21°C the insect is only just able to maintain its population at the higher concentration of deltamethrin. At 32.3”C, the population is declining at the higher concentration of pirimiphos-methyl. The estimates of I’ are likely
TARLE 3. THE ~~~NSIC
RATE OF INCREASE PER WEEK OF S.oryxe RIN AND PIRIMIPHOS-METHYL
Temperature
( CI
Control
'1
0.336 0.679 0.465
27
32.3
Deltamethrin 0.05 mg kg- ’ 0.1mg kg I 0.171 0.632 0.345
0.083 0.451 0.247
EXPOSED TO D~LTAMETH-
Pirimiphos-methyl 0.35 mg kg I 0.3 mg 0.322 0.557 0.222
kg- I
0.2X5 0.24 I -0.073
The Effects of Pesticides
upon the Population
Growth
of Si!oplri/us OTJJXY
29
to be slight overestimates, due to the use of data from only the first 4 weeks of reproductive life, which are the most productive (BIRCH, 1953). There are several important conclusions to be drawn from these results. If the grain were hot ( -33°C) the results suggest that is would be more appropriate to apply pirimiphos-methyl. whereas if the grain were cool, deltamethrin would be more appropriate. The application rates necessary to achieve a population growth rate of zero would be at 32.3,-C and 0.1 mg kg- ’ deltamethrin at approximately 0.4 mg kg- ’ pirimiphos-methyl ?I ‘C. What uould be the best strategy to employ at the intermediate temperature of 27-C, the temperature most suitable for the growth of S. o~v:tre populations and which is commonly observed in grain at in-loading in bulk-storages in Australia? Since the grain will cool anyway. the speeding up of the process, by means of aeration, will produce conditions under which deltamethrin would be most effective. LONGSTAFF (198 1) has shown that control of S. oryzae could be achieved by combining cooling to 21°C and the use of about :j-lo”, of the deltamethrin necessary on grain at 27’C. Apart from the considerable cost benefits of such a strategy. the reductions in the level of residual deltamethrin would be a major advantage, because it has a relatively high mammalian toxicity (CASIDA et al., 1979). A~,lirloICIYdyYItIYllts-The authors acknowledge the financial technical assistance of Messrs J. Anderson and G. Smith.
assistance
of the Australian
Wheat
Board
and the
REFERENCES BIRCH, L. C. (1948) The intrinsic rate of natural increase of an insect population. J. Anim. Ecol. 17, 15-26. BIRTH, L. C. (1953) Experimental background to the study of the distribution and abundance of insects. Ecoloy) 34, 698-7 I I. BLISVI>I.. J. R. t 1071) 4 C‘ririccrl Rwi~+v o/ tlrr Tt~churyws for Tesrirq /rlsrc,ric,idrs. 2nd ed. Commonwealth Agricultural Bureau. Slough. England. Chsu~ J. E.. GAI.C;HAN. L. C. and R1.z~. L. 0. (1979) Comparative metabolism of pyrethroids derived from ?-phenoxybenzyl and r-cyano-2-phenoxybenzyl alcohols. In Arlt-~ncrs irl Prsrici& Scie~(,r (Edited by GrossH~‘.I{L~ K). Part 2. pp. I82 I X9. Pergnmon Press. Oxford. DESMARCHELIER. J.. BENC~STO~,M.. CONN~LL, M., MINETT. W., MOORE.B., PHILLIPS,M.. SNELSDYJ, J.. STI~XA. R. and TUCKER. K. ( 1980) .il Coil~rhorutiw Srud,v of Rcsidtws of’ Mrthorrcr~fu.s, Clllorp~rifbs-/tl~t~?~/. Fcrlitrothim. Mulathio~, urld Pirirniphos-nlcth?l on Wheat. II. Rates qf‘ihcuy. CSIRO Division of Entomology Report No. 20. CSIRO. Canberra. Australia. LESLIE.P. H. (1945) On the use of matrices in certain population mathematics. B~orrtetriku 33, 183-212. LONGSTAFF.B. C. (1981) The manipulation of the population growth of a pest species: an analytical approach. J. uppl. Em/. 18, 127-736. SOL.OMON. M. E. (I 95 I ) Control of humidity with potassium hydroxide. sulphuric acid, and other solutions. Hull.
e/it. Re!.
42, 53.1-554.
USHER. M. B. (19:12) Developments in the Leslie Matrix model. In .Vf‘trllel,luticttI hlodt,/.s in Eco/og!, (Edited J. N. R. Jeffers) pp. 19-60. Blackwell Scientific. Oxford.
by
pp.
Printed in Great Britain. All rights
reserved
'S-29.1983
0022-474X/83/010025-05$03.00/0
Copyright 0 1983Pergamon Press Ltd
THE EFFECTS OF THE TEM.PERATURE-TOXICITY RELATIONSHIPS OF CERTAIN PESTICIDES UPON THE POPULATION GROWTH OF SITOPHILUS ORYZAE (L.) (COLEOPTERA: CURCULIONIDAE) B. C. LONGSTAFF
and J. M. DESMARCHELIER
CSIRO Division of Entomology, P.O. Box 1700. Canberra City. A.C.T. 2601. Australia (Receiced Abstract-An
irl jiml
form
15 July 1982)
experiment to assess the effects of temperature upon the toxicity of two pesticides
to Sitopldus
oryzae is described. The pesticides used, pirimiphos-methyl and deltamethrin. were shown to hive opposite relationships with temperature. The consequences of these relationships are discussed in relation to the population growth of S. oryzuu and, in particular. to the use of cooling in combination with low levels of pesticide as an integrated control measure for this and other pest species.
INTRODUCTION
THE RELATIONSHIPS between
the toxicity of insecticides and temperature have been extensively studied IBusvrr\ls. 1971). Such studies have practical relevance to grain protectants because the stored grain environment can be readily manipulated. Studies on the longterm effects of environmental variables on the toxicity of grain protectants can help to define the minimum amount necessary to prevent the growth of pest populations. The effects of such variables on the persistence, as distinct from the toxicity, of protectants was minimized, in the present study, by the selection of two persistent chemicals: pirimiphos-methyl and deltamethrin. Pirimiphos-methyl, an organophosphorus insecticide, and deltamethrin, ;.I pyrethroid, would be expected to show, respectively, positive and negative temperature effects upon adult mortality (BUSVINE, 1971). The aims of this study were to confirm this expectation with reference to Sitoplliltrs ory:ae (L.) and, more especially, to investigate the joint effects of grain temperature and sub-optimal levels of each pesticide on its population growth. MATERIALS
AND
METHODS
Both deltamethrin and pirimiphos-methyl were supplied as emulsifiable concentrates, with 25 and 900 g per litre a.i., respectively. The experimental design consisted of using three temperalures (21, 27 and 32.3”C) at each of which five treatments were employed: an untreated control, two levels of pirimiphos-methyl, and two levels of deltamethrin. The duration Iof the experiment was four weeks and each treatment was replicated eight times for each week. The levels of deltamethrin employed were nominally 0.05 and 0.1 mg kg-’ and it was synergised with 8 g per litre piperonyl butoxide. The levels of pirimiphos-methyl employed were 0.25 and 0.4 mg kg- ‘. For each of the treatments, Australian Standard White wheat, of the variety Olympic, was conditioned to achieve a grain m.c. of 12.5%. The pesticides were applied to 4.5 kg of wheat, at appropriate levels, by pipette at a.rate of 0.002 litres per kg. Pirimiphos-methyl was applied in an acetone solution, deltamethrin in water. The pesticide and wheat were mixed manually and then left to equilibrate for one week at 3O”C, before being remixed and used for the bioassay experiments. The treated wheat was not analysed to confirm dosage and so application must be considered as nominal. Any breakdown of the pesticides during the experimental
26
B. C. LONGSTAFF and
J. M. DESMARCHELIER
period would be negligible and would be within the range of accuracy of the analytical methods used (DESMARCHELIERet al., 1980; J. SNELSON, personal communication). Following mixing, the wheat was divided up into 45 g lots (8 replicates x 4 weeks x 3 temperatures for each treatment) and placed in glass jars with perforated screw tops. Six pairs of O-24 hr old S. oryzae were then placed in each jar and 32 jars of a given treatment were placed together in an incubator maintained at the desired temperature. The grain m.c. was maintained by means of trays of saturated sodium bromide solution. This gave an e.r.h. of 55% (SOLOMON, 1951). After 1 week, the number of live insects remaining in each jar was assessed and these were then transfered to the next set of eight jars. The used wheat was incubated until all progeny had emerged and any emergent adults were removed weekly. The procedure was repeated each week for the duration of the experiment. The data obtained are presented as the means i: SE of the eight replicates. RESULTS AND DISCUSSION Pirimiphos-methyl exhibited a consistent, positive temperature effect on adult mortality in that, for each time period and each level of exposure, mortality increased over the range 21&32.3”C (Table 1). Deltamethrin was more toxic at 21°C than at either 27 or 32.3”C, but there were no significant differences in its toxicity between the latter two temperatures (Table 1). In terms of fecundity. the situation was more complex. Fecundity has been defined in this study as the ratio of the number of female offspring emerging to the mean number of females alive during the period of exposure. assuming a sex-ratio of 1 : 1. At all temperatures, the lower application rate for pirimiphos-methyl (a nominal 0.25 mg kg- ‘) had only a minor effect upon the number of progeny produced per female whereas at the higher rate (a nominal 0.4 mg kg- ‘) there was a positive relationship hith temperature: the higher the temperature the greater the reduction in fecundity (Table 2). This reduction increased with time of exposure. Deltamethrin showed the least effect at 27”C, where the fecundity for the first week of exposure was actually greater, at the lower application rate. than that of the control cultures and there was a similar increase in fecundity in the first week at 32.3 C (Table 2). No explanation of this phenomenon is offered. In most instances. the pesticide did not greatly affect the fecundity in the first week of exposure, but reductions became more pronounced with time. The effects of these pesticides upon the demographic potential of this species may be readily seen by plotting time, (x), against I\-L?,,which is the product of the proportion of females alive at time X, (I,), and the mean number of female progeny produced in a unit
TABLEI. THE CIJMIJLATM SURVIVAL OF MATURE S. OT~XC ~XPOSFIITO PIRIMIPHOS-MLTH~I. :\\I)IXL.IAMI.THKI~ OVER A PERIOD OF 4 WEEKS. THE RESULTS ARF PRESENTED AS MAN WMLLATIW SIKWIAL (I,)2 SE Treatment Control
Deltamethrin and piperonyl butoxide (0.05 mg kg- ‘) Deltamethrin and piperonyl butoxide (0.1 mg kg-‘) Pirimiphosmethyl (0.25 mg kg ’ ) Pirimiphosmethyl (0.4 mg kg- ‘)
Weeks
Temperature (‘C)
1
2
21
1.00
I .oo
21
1.00
32.3 21 27 32.3 21 27 32.3 21 27 32.3 21 27 32.3
1.00 0.71 0.88 0.95 0.42 0.69 0.84 0.97 0.95 0.56 0.95 0.47 0.17
0.99 1.00 0.50 0.80 0.89 0.30 0.58 0.72 0.96 0.73 0.22 0.89 0.24 0.01
& + f f f * f f f + * *
0.14 0.07 0.08 0.10 0.16 0.14 0.05 0.04 0.17 0.07 0.09 0.12
3
3
1.00 * 0.02 + f + & f * i & * i k +
0.1 I 0.09 0.07 0.13 0.17 0.09 0.06 0.13 0.14 0.13 0.1 1 0.02
0.99 0.99 0.42 0.76 0.86 0.22 0.55 0.61 0.96 0.47 0.13 0.87 0.03 0.01
* * * i i i * + f i * * k f
0.02 0.02 0. I I 0.1 I 0.07 0.12 0.15 0.10 0.05 0.16 0.10 0.1’ 0.06 0.02
0.99 0.96 0.32 0.70 0.75 0. I4 0.50 0.50 0.91 0.38 0.1 I 0.77 0.01 0.0
& * * * * * * * i i
0.07 0.05 0. I2 0.09 0.13 0.09 0. I3 0. I2 0.06 0.20 i 0.1 I f 0.16 * 0.02
The Effects of Pesticides
TABLE
2. THE
AGE-SPECIFIC
FECUNDITY
upon the Population
(0,)
OF S.
oryxe.
PROGENY
Growth
THE
DATA
PER FEMALE
i
of Sitophilus
ARE
21 27 32.3 21 27 32.3 21 27 32.3 21 27 32.3 21 27 32.3
Deltamethrin and piperonyl butoxide (0.05 mg kg- r) Deitamethrin and piperonyl butoxide (0.1 ray klj_ I) Pirimiphosmethyl (0.25 mg kg- ‘) Pirimiphosmethyl (0.4 mg kg- t)
NUMBER
OF
LIVE
FEMALE
Weeks
I
(“C)
Control
MEAN
27
SE
Temperature
Treatment
THE
oryzae
3.2 9.8 3.6 2.5 16.3 9.1 2.0 7.0 4.1 6.2 9.1 4.5 2.6 6.3 2.9
z
f 1.3 + 5.3 f 2.1 2 1.2 k 2.0 k 4.6 ri_ 1.3 & 2.9 f 1.7 k 4.1 f 2.0 * 2.1 i 1.3 i 3.6 + 2.3
8.9 16.4 7.8 4.4 18.0 6.0 3.5 9.1 2.9 8.2 15.1 8.2 6.1 11.8 1.3
* + k f + f & f * f f k f f +
3 3.4 5.2 4.1 2.3 3.2 2.7 3.0 4.5 1.4 2.5 3.9 3.1 3.0 10.7 1.5
8.7 16.4 7.3 4.1 13.2 3.3 2.8 7.9 2.4 10.4 17.0 6.2 9.0 6.0 0.0
4
f f * + f * f & k * + k * +
1.3 6.6 3.4 2.2 3.8 2.5 2.1 6.5 0.9 3.3 8.1 5.5 4.4 7.2
8.7 16.1 7.1 1.9 16.9 0.3 0.8 6.7 0.7 5.1 17.1 6.4 3.9 0.0 0.0
f k * f + + k + & * * + +
1.6 4.9 3.4 3.5 5.5 0.2 1.6 5.2 0.1 2.3 6.8 5.9 1.3
of time by a female of age x,uX (Fig. 1). BIRCH (1948) considered the product of l,m,, where m, is the number of female eggs laid by a female of age .Y in a unit of time. He modified I, to include the effect of immature mortality, whereas it is implicit in the term v,. At the coolest temperature (21”(Z), the deltamethrin treatments showed very low, flat response curves over time. In the populations exposed to pirimiphos-methyl, the values initially rose, as did that for the control populations, but then declined sharply at the end of the experimental period. Because, at 21°C the first 4 weeks of reproductive life contributed almost 60% of the population growth rate (BIRCH, 1948), the major reductions brought about by the low levels of deltamethrin would severely inhibit population growth at this temperature. At the warmest temperature (32.3”(Z), pirimiphos-methyl was more effective than deltamethrin during the first two weeks, but all treatments converged to almost lOOO,/,control by the end of the experimental period. A summation of IXv, over rate (BIRCH, the experimental period provides an estimate of &, the net reproductive
Id
2 2
18
le.
16.
14
14
12
-
10
_
42-
IC)
12.
.-/s_. lo
0’ ,‘.\
a6-
ibi
I
18
.
/
I’
.’
,’
‘\ \ \ \o \
\
/ I/ /I .q
\ .
o-o--o .---•-__
0 1
a-
2
\ \. s---._
3
4
6-
l_--.. -. 0.
4-
‘\.
l --_. ‘\
2t o
*
2-
\ \ \.
12
-=--_._ 40 3
x
4-
“Qx_ l I 1
-_
”
‘;=zx, \ --*a
-*=--,_-_)_
2
3
4
(weeks)
FIG. 1. The effect of pesticide treatment on demographic performance as indicated by the product of cohort survival and age-specific fecundity (I,v,) (A-A) Control; (O---O) 0.25 mg kgg’ pirimiphos-methyl; (B-m) 0.4 mg kg- ’ pirimiphos-methyl; (C-O) 0.05 mg kg- ’ deltamethrin; (t-0) 0.1 mg kg-’ deltamethrin (a) 21°C. (b) 27”C, (c) 32.3’C.
B. C. LONGSTAFF and J. M. DEWARCHELIER TABLE
i. THE
NET
REPRODUCTIVE
Temperature (-C)
Control
RO
‘I
21 32.3
TO
DELTAMETHRIN
AND
Pirimiphos-methyl Deltamethrin 0.05 mg kg- ' 0.1mg kg ’ 0.25 mg kg- ’ 0.1mg kg- ’
19.5
O0of control RO "o of control R, ","of control
EXPOSED
RATE OF S. oryxw PIRIMIPHOS-METHYL
58.7
6.4 21.3 50.8
2.5 8.5
x.4 96.3
18.8 63.7
76.4
86.5 16.7
11.9 30.5 7.5
34.0 57.9 5.8
6.0 10.2 0.5
63.1
28.3
72.0
2.0
1948). These estimates and their relationship to the corresponding control values are given in Table 3. The data presented above may be used to derive an estimate of the intrinsic rate of increase, r, which describes exponential growth. Thus, :V, = NOerr where N, is the initial population size and N, the population at time t. This is readily done using a Leslie-type matrix model (LESLIE, 1945; USHER, 1972). This model is a set of difference equations that include age-specific mortality and reproductive rates. Thus. we have a matrix. M: 0
0
0
0
v,
v,
v,
v4
.
lo...
0 .
Ol...
.
.Ol.. M=
.
1..
.
.
.
.
.
.
P 1.2
.
.
.
.
.
0
P 2.3 .
P,,,
0
where Vi is the number of female progeny per female adult of age i: Pi,;+ 1 is the rate of survival from age i to i + I. In the example above there are 4 immature age-classes, each of 1 week duration. This is the situation at 27’C. but at ?I and 32.3~C the immature periods are protracted to eight and five weeks respectively. Appropriate changes must be made to the matrix when considering these temperatures. Immature survival is given as unity in each class because the mortality is implicit in the values of Vi. The calculation of the dominant eigenvalue of such a matrix provides one with an estimate of the finite rate of increase (i) (BIRCH, 1948; LESLIE, 1945), the natural logarithm of which is r. The latter is the intrinsic rate of increase per unit time and a value of zero indicates that the population size does not change. Estimates of r were calculated and are shown in Table 4. From this analysis it is clear that, at 21°C the insect is only just able to maintain its population at the higher concentration of deltamethrin. At 32.3”C, the population is declining at the higher concentration of pirimiphos-methyl. The estimates of I’ are likely
TARLE 3. THE ~~~NSIC
RATE OF INCREASE PER WEEK OF S.oryxe RIN AND PIRIMIPHOS-METHYL
Temperature
( CI
Control
'1
0.336 0.679 0.465
27
32.3
Deltamethrin 0.05 mg kg- ’ 0.1mg kg I 0.171 0.632 0.345
0.083 0.451 0.247
EXPOSED TO D~LTAMETH-
Pirimiphos-methyl 0.35 mg kg I 0.3 mg 0.322 0.557 0.222
kg- I
0.2X5 0.24 I -0.073
The Effects of Pesticides
upon the Population
Growth
of Si!oplri/us OTJJXY
29
to be slight overestimates, due to the use of data from only the first 4 weeks of reproductive life, which are the most productive (BIRCH, 1953). There are several important conclusions to be drawn from these results. If the grain were hot ( -33°C) the results suggest that is would be more appropriate to apply pirimiphos-methyl. whereas if the grain were cool, deltamethrin would be more appropriate. The application rates necessary to achieve a population growth rate of zero would be at 32.3,-C and 0.1 mg kg- ’ deltamethrin at approximately 0.4 mg kg- ’ pirimiphos-methyl ?I ‘C. What uould be the best strategy to employ at the intermediate temperature of 27-C, the temperature most suitable for the growth of S. o~v:tre populations and which is commonly observed in grain at in-loading in bulk-storages in Australia? Since the grain will cool anyway. the speeding up of the process, by means of aeration, will produce conditions under which deltamethrin would be most effective. LONGSTAFF (198 1) has shown that control of S. oryzae could be achieved by combining cooling to 21°C and the use of about :j-lo”, of the deltamethrin necessary on grain at 27’C. Apart from the considerable cost benefits of such a strategy. the reductions in the level of residual deltamethrin would be a major advantage, because it has a relatively high mammalian toxicity (CASIDA et al., 1979). A~,lirloICIYdyYItIYllts-The authors acknowledge the financial technical assistance of Messrs J. Anderson and G. Smith.
assistance
of the Australian
Wheat
Board
and the
REFERENCES BIRCH, L. C. (1948) The intrinsic rate of natural increase of an insect population. J. Anim. Ecol. 17, 15-26. BIRTH, L. C. (1953) Experimental background to the study of the distribution and abundance of insects. Ecoloy) 34, 698-7 I I. BLISVI>I.. J. R. t 1071) 4 C‘ririccrl Rwi~+v o/ tlrr Tt~churyws for Tesrirq /rlsrc,ric,idrs. 2nd ed. Commonwealth Agricultural Bureau. Slough. England. Chsu~ J. E.. GAI.C;HAN. L. C. and R1.z~. L. 0. (1979) Comparative metabolism of pyrethroids derived from ?-phenoxybenzyl and r-cyano-2-phenoxybenzyl alcohols. In Arlt-~ncrs irl Prsrici& Scie~(,r (Edited by GrossH~‘.I{L~ K). Part 2. pp. I82 I X9. Pergnmon Press. Oxford. DESMARCHELIER. J.. BENC~STO~,M.. CONN~LL, M., MINETT. W., MOORE.B., PHILLIPS,M.. SNELSDYJ, J.. STI~XA. R. and TUCKER. K. ( 1980) .il Coil~rhorutiw Srud,v of Rcsidtws of’ Mrthorrcr~fu.s, Clllorp~rifbs-/tl~t~?~/. Fcrlitrothim. Mulathio~, urld Pirirniphos-nlcth?l on Wheat. II. Rates qf‘ihcuy. CSIRO Division of Entomology Report No. 20. CSIRO. Canberra. Australia. LESLIE.P. H. (1945) On the use of matrices in certain population mathematics. B~orrtetriku 33, 183-212. LONGSTAFF.B. C. (1981) The manipulation of the population growth of a pest species: an analytical approach. J. uppl. Em/. 18, 127-736. SOL.OMON. M. E. (I 95 I ) Control of humidity with potassium hydroxide. sulphuric acid, and other solutions. Hull.
e/it. Re!.
42, 53.1-554.
USHER. M. B. (19:12) Developments in the Leslie Matrix model. In .Vf‘trllel,luticttI hlodt,/.s in Eco/og!, (Edited J. N. R. Jeffers) pp. 19-60. Blackwell Scientific. Oxford.
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