A study on insecticide resistance in Tribolium castaneum (Herbst) (Coleoptera, Tenebrionidae) in Malawi (Central Africa)

J. stored Prod.Res.,1972,Vol. 8, pp. 183-191.

A Study

Pergamon Press. Printed in Great Britain.

Resistance in Tribolium castaneum (Herbst) (Coleoptera, Tenebrionidae) in Malawi _ (Central Africa) A. H.

on Insecticide

PIETERSE,

Department

G. G. M. SCHULTEN* and W. KUYKEN

of Agricultural

Research, Royal Tropical The Netherlands

(First received 2 1 February f972,

Institute,

and infinal form 15 June

Amsterdam,

1972)

Abstract-Seventeen strains of Tribolium castaneum, collected from warehouses and stores throughout Malawi, were tested for susceptibility to lindane and malathion. In all strains beetles resistant to lindane were found and the same was true for malathion resistance in eleven strains. The malathion-resistant strains showed cross-resistance to bromophos and the malathion resistance was not significantly affected by the synergist triphenylphosphate. It is therefore considered probable that the resistance in the eleven malathion-resistant strains was of the non-specific type. Pirimiphos-methyl was very effective against malathion-resistant strains. Resistance in Tribolium castaneum is widespread in Malawi. Probably it developed in the large warehouses, where insecticides have been extensively used for a number ofyears, and from there has spread to smaller warehouses and stores through normal trade channels. INTRODUCTION

THE RUST-RED flour beetle, Tribolium cmtuneum (Herbst), is a common pest of stored produce in Malawi. Control of this insect is dependent in large measure on the use of chemicals. Recently, resistance to lindane and malathion in a strain from a store in Malawi was reported by DYTE and BLACKMAN (1970). This raised the question whether the resistance is restricted to this store or also occurs in other depots in this country. Insecticides are used in Malawi in the warehouses of the Agricultural Development and Marketing Corporation (ADMARC). This is the main organization which deals in produce like maize, groundnuts, pulses and rice. The chemrcal control of stored product insects was started more than 20 years ago with the introduction of DDT for spraying bagged produce. This was soon replaced by lindane and malathion (HALL, 1950; SALMOND, 1957; SWEENY, 1962). The frequency of application increased over the years because of frequent reinfestation of fumigated produce by Ephestia cautella (Walker). Until 1970, the walls of warehouses were sprayed twice a year with lindane, the floors were dusted with * University

of Malawi,

Chancellor

College,

Limbe, 183

Malawi

184

A. H. PIETERSE,G. G. M. SCHULTENand W. KUYKEN

lindane, and the stacks of bagged produce were sprayed weekly with lindane or malathion alternately. Since then spraying of walls and dusting of floors has been stopped, and bagged produce is sprayed at 2-week intervals. In general, no pest control takes place in warehouses and stores which do not belong to ADMARC. Since insecticides have been used extensively during a relatively long time, resistance may have developed on a large scale. The object of the present investigation was to obtain a general picture of the occurrence of insecticide resistance in Tribolium castaneum throughout Malawi. MATERIALS

AND METHODS

Seventeen strains of Tribolium castaneum (Herbst) were collected in different warehouses and stores throughout Malawi. Details of their origin are given in Table 1. The location of these warehouses and stores is shown in Fig. 1. All strains were from maize except No. 16 from maize bran and No. 17 from wheat flour. There was intensive pest control in all large warehouses, some control in small warehouses, and no control in the stores. A susceptible strain of unknown origin (SLS), which had been in culture for several years, was used as a control strain. The strains were reared in

-YlOOkm

FIG. 1. Location of warehouse and stores in Malawi from where the different strains of Tribolium ca-staneum, which were tested for susceptibility to different insecticides in the present investigation, were collected.

-

Large warehouse Same warehouse as No. 2

Balaka Balaka

Lilongwe Lilongwe Luchenza

Luchenza Limbe

Salima Salima

Bolero

Nassawa Nkhata Bay Kasungu Chalandewah Bunda College Kaporo

2 3

4 5 6

87

9 10

11

I2 13 14 15 16 17

Small warehouse Small warehouse Small warehouse Store Store Store

Small warehouse

Large warehouse Same warehouse as No. 9

Same warehouse Large warehouse as No. 6

Large warehouse as No. 4 Same warehouse Large warehouse

Maize in transit to Zambia (exported from Albania)

Collected (from)

KNOCKDOWN

Balaka

(at)

Collected

AND

1

Strain (No.1

TABLE 1. DETAILSOF ORIGIN

May Nov. June Dec. May Nov.

1971 1970 1971 1971 1971 1970

May 1971

Mar. 1971 May 1971

May 1971 May 1971

Sep. May 1970 1971 Dec. 1970

Nov. 1969 Nov. 1970

12 98 1 44 66 10

53

1

32 7:

6 8 68

7 73

58

Lindane (2.5%)

100 100 19 39 67 16

99

100 26

58 16

100 36 100

86 100

66

Malathion (0.5%)

Knockdown (%)

91 50 43 76

69

83

58 88

24 100

32

66

Bromophos (0.5%)

OF STRAINS OF Tribolium castaneum FROMMALAWI

Nov. 1970

Date of collection

RESPONSES

38 100 22 54 73 10

56

72 32

53 15

16 8 81

54 81

87

Highest per cent knockdown obtained at O-25% lindane

: 3

B

? 0: E P’ 3

I! E’

p B

cr. fg

186

A. H. PIETERSE, G. G. M. SCHULTEN and W. KIJYKEN

glass jars at 27 & 1°C and 70% r.h. on a mixture ofwhole wheat flour and dried yeast powder (18 : 1 by vol.). The test method was essentially similar to that described by CHAMP and CAMPBELLBROWN (1970a). The insecticide was dissolved in a 3 : 1 : 1 mixture of petroleum ether (b.p. 60-80”), acetone and risella oil. Aliquots of 0.5 ml were spread on Whatman No. 1 paper with a diameter of 7 cm. For convenience, deposits were referred to as concentrations based on non-volatile solvent, i.e. risella oil, rather than as dose-unit area of filter paper. The insecticides used were high grade technical samples as follows: lindane 99 - 6% ; malathion 96% ; bromophos 98% ; pirimiphosmethyl (2-diethylamino-6-methylpyrimidin-4-yl dimethyl phosphorothionate) 94%. Impregnated papers were dried by standing overnight on trays under a hood. Glass rings with a diameter of 5 cm and 2.5 cm high, coated with ‘Fluon GP 1” to prevent escape of insects up the walls, were used to confine the insects to the treated surface. Response was assessed as knockdown after 24 hr continuous exposure at 25” and 70% r.h. Knockdown was defined as inability of insects to stand and walk. A gentle push with a brush was usually sufficient to determine in which category an individual was to be classed. Normally five replicates, each of ten adults, were used for each concentration. Experiments with the synergist triphenylphosphate were done with 20 replicates. Each experiment was repeated at least once.

RESULTS

Lindane resistance was detected in all seventeen strains of Tribolium castaneum. The knockdown percentages after 24 hr at different concentrations (up to the extreme high concentration of 25 per cent) of lindane are shown in Fig. 2. The knockdown line of the susceptible strain (SLS) sh ows clearly the difference between resistance and susceptibility. The KD,, (dose at which knockdown is 50 per cent) of the susceptible laboratory strain ,was O-145 per cent. At 2 - 5 per cent, the concentration which was used by CHAMP and CAMPBELL-BROWN (1970b) as a discriminating dose to differentiate between lindane-susceptible and lindane-resistant strains, the knockdown percentage of SLS was 100 per cent. The knockdown percentages of seventeen strains from Malawi at 2 *5 per cent and the highest knockdown percentages which were obtained at the concentrations used (O-25%) are shown in Table 1. In Fig. 3 the results are shown of the tests with malathion. The susceptible laboratory strain was again used as a control. The strains 1, 2, 5, 7, 8, 10, 11, 14, 15, 16 and 17 proved to be malathion resistant, the others being susceptible. The concentration of 0.5 per cent was used as a discriminating dose (at this concentration the knockdown of the susceptible strain is about 99.9 per cent). The knockdown percentages of the susceptible strains from Malawi at this concentration were 100 per cent (see Table 1). The KD,, of the susceptible strains was about 0.1 per cent (see Fig. 3). The knockdown percentages of the resistant strains at 0.5 per cent are shown in Table 1. At 2.5 per cent the knockdown was 100 per cent in all the resistant strains with the exception of the strains 5, 10 and 15. However, no beetles of these three strains survived a concentration of 4 per cent. The malathion resistant strains, the susceptible strain 6, and the susceptible laboratory strain (SLS) were also tested with bromophos. The results are shown in Fig. 4. The KD, values of 6 and SLS were about 0.1 per cent. These strains were

Insecticide Resistance in Tribolium castaneum

187

clearly susceptible to bromophos. The malathion resistant strains on the other hand showed resistance to bromophos. The concentration of 0.5 per cent was used as a discriminating dose, the knockdown percentage of SLS at this concentration was about 99 *9 per cent, and that of strain 6 was 100 per cent. The knockdown per-

(b)

SLS YY8

go-

; 5

50-

/ rm

:: y’

IOI-

I 001

I

I

I

I

I

0 I

I.0

25

IO

25

Concentration,

%

FIG. 2. Knockdown of Tribolium castaneum strains from Malawi at different concentrations of lindane after 24 hr. (a) : strains 1-6. (b) : strains 7-12. (c) : strains 13-17. The knockdown line of the susceptible laboratory strain SLS is used as control.

centages of the malathion resistant strains at this concentration are shown in Table 1. All the resistant insects died at a concentration of 2 *5 y0 bromophos. In order to distinguish specific and non-specific malathion resistance in Tribolium custuneum, the resistant strains were tested at a concentration of O+5o/omalathion supplemented with 10% triphenylphosphate. The knockdown percentages were

188

A. H.

PIETERSE,

G. G. M.

and W. KUYKEN

SCHULTEN

compared with the knockdown percentages at 0 *5% malathion alone. Triphenylphosphate did not significantly affect the malathion resistance in these strains, the knockdown percentages were about the same when the synergist was added.

-1/if Pf I

1

II

I

I

,SLS

4(9”

99

8 90

(b)

.-•

; 50 z 4 8

'2, /

IO

*IO @I

7

I

II

I

I

(cl

99I5

go50-

IOI-

I

I

001

I

II

0.1

0.5

Concentmtion,

I I.0

2.5

I IO

%

FIG. 3. Knockdown of Tribolium castaneum strains from Malawi at different concentrations of malathion after 24 hr. (a) : strains l-6. (b): strains 7-12. (c) : strains 13-17. The knockdown line of the susceptible laboratory strain SLS is used as control.

In Fig. 5 the results of the experiments with pirimiphos-methyl are presented. The malathion susceptible strains 4 and 6, and the malathion resistant strains 1, 5, 7, 8 and 11 were tested with this insecticide. All these strains did not survive the relatively low concentration of 0.25 per cent, with the exception of strain 5, The knockdown percentages of strain 5 were 60 per cent at a concentration of 0.25%, 81% at O*3Oo/oand 93% at O*4Oo/o.All the beetles of strain 5 died at O.5Oo/oof pirimiphosmethyl.

Insecticide Resistance in Tribolium

castaneum

(b)

II 0.5

I 0.01

0. I

I 23

IO

I IO

Concentration,% FIG. 4. Knockdown of Tribolium

castuneum strains from Malawi at different concentrations of bromophos after 24 hr. (a) : the malathion-susceptible strain 6 and the malathionresistant strains 1,2, 5, 7 and 8. (b) : the malathion-resistant strains 10,11, 14,15, 16 and 17. The knockdown line of the susceptible laboratory strain SLS is used as control.

99

90

50

IO

I

I 0.1

I

I

I

o-25 o-5 I.0

Concentration,

I IO

%

5. Knockdown of the malathion-susceptible strains 4 and 6 and the malathionresistant strains 1, 5, 7, 8 and 11 of Tribolium castaneum from Malawi at different concentrations of pirimiphos-methyl after 24 hr.

FIG.

189

190

A. H.

PIETERSE

G. G. M.

SCHULTEN

and W. KUYKEN

DISCUSSION

From different parts of the world lindane resistance (ANON, 1958; BROWN, 1963; CHAMP and CAMPBELL-BROWN, 1969; DYTE and BLACKMAN, 1970) and malathion resistance (PARKIN, 1965 ; SPEIRS et al., 1967; TOPPAZODA et al., 1969; CHAMP and CAMPBELL-BROWN, 1970b; DYTE and BLACKMAN, 1970) in Tribolium castaneum have been reported, including Malawi (DYTE and BLACKMAN, 1970). The present survey shows that resistance in Malawi is widespread. The occurrence in the warehouses of the ADMARC is not surprising, taking into account the rather extensive use of insecticides over a prolonged period. The fact that resistance was also detected in strains from warehouses and stores where insecticides have been rarely or never used, strongly suggests that resistant beetles are spread through trade within Malawi. The presence of resistant beetles on maize in transit (strain 1) demonstrates that resistant strains can also be transferred from country to country. Consequently, it is impossible to conclude whether the resistance gene(s) originated in Malawi or were introduced from elsewhere. It may be assumed that resistance genes can easily maintain themselves in unselected populations as resistance was found in strains from warehouses where insecticides have never been used. Thus, very probably resistance genes are easily integrated into the gene pool of susceptible populations without an apparent negative effect on fitness. Malathion resistance in Tribolium castaneum in Malawi is not as common as resistance for lindane, but also occurs in most warehouses and stores. DYTE and BLACKMAN (1970), who tested many strains from different countries of the world, more frequently encountered specific malathion resistance than the non-specific type. Specific malathion resistance can be completely suppressed by the synergist triphenylphosphate and is probably due to enhanced detoxication by carboxyesterases (DYTE and ROWLANDS, 1968). DYTE and BLACKMAN(1970) observed that in a strain from the Balaka depot malathion resistance was significantly affected by triphenylphosphate. However, triphenylphosphate did not overcome the malathion resistance completely. In the present work all the malathion resistant strains appeared to be of the non-specific type, including one strain from the Balaka depot. There were no significant differences between the knockdown values at O*5o/omalathion and 0.5% malathion supplemented with 10% triphenylphosphate. The conclusion that the resistance is non-specific is supported by the fact that all the malathion resistant strains were cross-tolerant to bromophos. Pirimiphos-methyl on the other hand was very effective against malathion resistant Tribolium castaneum. From the results of this survey it can be concluded that a critical situation has been reached. In practice, however, this is as yet not so, because the pest control staff of the ADMARC spots incipient infestation from the very beginning and cuts it short by fumigation. Ephestia cautella, the tropical warehouse moth, is the major pest in the depots (SCHULTEN, 1970), while Tribolium castaneum is of much lesser importance. At present a considerable extension effort is made to familiarize storekeepers and farmers with improved storage methods. Malathion is recommended in Malawi because it is cheap and safe. Failures in the control of Tribolium are likely to occur in the near future in small warehouses and stores where there are at present no alternative methods of control, like fumigation. Therefore testing of alternative insecticides under field conditions is urgently needed.

Insecticide Resistance in Tribolium

castaneum

191

Acknowtedgenrents-The assistance of the Pest Control Supervisors of the ADMARC is greatly appreciated. The second author is seconded to the University of Malawi by the Royal Tropical Institute, Amsterdam, The Netherlands. The authors are grateful to Dr. G. VERHAAR,head of the Product Research Division of the Department of Agricultural Research of the Royal Tropical Institute, for critically reading the manuscript.

REFERENCES ANON (1958) Groundnuts. Rep. W. Afr. stored Prod. Res. Unit 1957, 17-32. BROWN, A. W. A. (1963) Insect resistance-I. Nature and prevalence of resistance. Fm Gem. 126( IO), 22224,

28.

CHAMP,B. R. and CAMPBELL-BROWN, M. (1969) Genetics of lindane resistance in Tribolium castaneum (Herbst) (Coleoptera, Tenebrionidae). J. stored Prod. Res. 5, 399-406. CHAMP, B. R. and CAMPBELL-BROWN, M. (1970a) Insecticide resistance in Australian Triboiium castaneum (Herbst)-I. A test method for detecting insecticide resistance. J. stored Prod. Res. 6, 53-70.

CHAMP, B. R. and CAMPBELL-BROWN, M. (I 970b). Insecticide resistance in Australian Tribolium castaneum (Herbst)-II. Malathion resistance in eastern Australia. J. stored Prod. Res. 6, 11 I-131. CHAMP, B. R. and CRIBB, J. N. (1965) Lindane resistance in Sitofihilus oryzae (L.) and Sitophilus zeamais Motsch. (Coleoptera, Curculionidae) in Queensland. J. stored Prod. lies. 1, 9-24. DYTE, C. E. and ROWLANDS,D. G. (1968) The metabolism and synergism of malathion in resistant and susceptible strains of Tribolium castaneum (Herbst) (Coleoptera, Tenebrionidae). J. stored Prod. Res. 4, 157-173.

DYTE, C. E. and BLACKMAN, D. G. (1970) The spread of insecticide resistance in Tribolium castaneum (Herbst) (Coleoptera, Tenebrionidae). J. stored Prod. Res. 6, 255-26 1. HALL, D. W. (1950) Report on Food Storage in Nyasaland. Colonial Office, London. PARKIN,E. A. (1965) The onset of insecticide resistance among field populations of stored-product insects. J. stored Prod. Res. 1, 3-8. SALMOND, K. F. (1957) Investigations into Grain Storage Problems in Nyasaland Protectorate. Colonial Research Publications No. 2 1. Colonial Office London. SCHULTEN, G. G. M. (1970) Preliminary results of field trials on the control of E,bh+xtia cautellaas a pest of bagged maize in Malawi. Pestic. Abstr. 16(4), 709-713. SPEIRS,R. D., REDLINGER,L. M. and BOLES,H. P. (1967) Malathion resistance in the red flour beetle. J. econ. Ent. 60, 1373-4. SWEENEY,R. C. H. (1962) Insects Pests of StoredProducts in Nyasaland. Eastern Districts Printers, Umtali, South Rhodesia. TOPPAZODA,A., ISMAIL,F. I. and ELDEFRA~~,M. E. (1969). Susceptibility of local strains of Sitophilur oryzae (L.) and Tribolium castaneum (Herbst) to insecticides. J. stared Prod. Res. 5, 393-397.