Proceedmqe of the 7 th International Working Conference on Stored-produci Protection - Volume 1 Cross resistance of phosphine-resistant insect pests of stored grain to fenitrothion and to chloropicrin LIang Yongsheng and Ran LI 1 Abstract Four strams of Rhyzopertha dommica (F.) (Coleoptera: Bostnchidae ) , 5 strams of Sitophsiu» oryzae (L.) ( Coleoptera: Curcuhonidae ) and 4 strains of Cryptolestes [erruqineus (Stepens) ( Coleoptera: Cucujidae) resistant to phosphme were tested for cross-resistance to femtrothion and chloropicnn Femtrothion resistance was determmed by using the impregnated-paper assays (FAO Method No. 15), and chloropicnn resistsnce was tested by fumigation in desiccators The results revealed that phosphine resistant strains of S. oryzae and C. [erruqmeus had no cross- resistance to chloropicnn or fenitrothion However, two phosphine-resistant strains of R dommica showed some resistance to fenitrothion With resistance factors of 2.94 and 5.24. Not all phosphme-resistant strains showed resistance to fenitrothion, therefore, we concluded that this resistance was due to previous exposure of insects to other insecticides. There was no resistance to chloropicrin in any strains of R. domuuca, Our results indicated that both ferutrothion and chloropicrin would be SUitablechemicals to be used in a rotation strategy to manage the development of resistance in these insect pests. Introduction Phosphme resistance m insect pests of stored grain IS becoming more prevalent and serious world wide (Dyte et al 1983; MIlls 1986; Pnce and MIlls 1988; Rajendran 1989; Taylor and Halliday 1986; Bekon et al. 1988; Ansell et al. 1991; Li and Li 1994; Liang 1994). In Chma, highly resistant strains of Rhyzopertha domuiuxi , Sitophtlus oryzae and Cryptolestes [erruqmeus have been detected m several storage wear-houses. Levels of resistance are high enough to cause control faIlures and threaten the continued use of thIS valuable fumIgant. The Chmese gram mdustry relIes heavIly on phosphine to control msect pests m stored gram. WhIle alternative treatments are avatlable and some new fumIgants are bemg developed but none have the 1 Chengdu Gram Storage Research Institute of Internal Trade Mmistry 95 Huapmfang Street, Chengdu, Sichuan, P R Chma combined attribute of phosphine of being easy to use, low m cost and ml or very low residues. Therefore, measures must be taken to manage or delay the development of resistance to this matenal in insect pests. A potentially effective resistance management tactic is to reduce selection by alternating use of phosphine With other treatments. Two Chemicals that are already registered for use m Chma and that could be used m such a rotation scheme are the gram protectant, femtrothion, and the fumigant, chloropicrin. However, for a rotation strategy to be successful there must be no cross-resistance between components of the strategy. Therefore, the current study was undertaken to determine whether phosphine-resistant strains of R. dominuxi; S oryzae and C ferrugineus were resistant to fenitrotnion and to chloropicrin. Materials and Methods Origin of strains The insect strains used m the experiments had the following origins: R. dominica : S-RD - Phosphme susceptible, from Chengdu, SIchuan R-CU - Phosphine resistant, from Chaozhou, Guangdong. R-HU - Phosphine resistant, from Shayang, HUbei R-YU - Phosphme resistant, from Yangchun, Guangdong R-A - Phosphine resistant, (QRD- 369) from Australia. S. oryzae: S-S02 - Phosphine susceptible, from Tongsheng, Haman. R-S06 - Phosphine resistant, Santai, SIchuan. R-S03 - Phosphine resistant, ZhanJIang, Guangdong. R-SOA - Phosphme resistant, (QSO- 335) from AustralIa. R-S013 - Phosphme reSIstant, from Guangdong-l. R-S014 - Phosphme reSIstant, from Guangdong-2. C ferrugineus: S-CF - Phosphme susceptible, from from from 612
Transcript
Proceedmqe of the 7 th International Working Conference on Stored-produci Protection - Volume 1
Cross resistance of phosphine-resistant insect pests of storedgrain to fenitrothion and to chloropicrin
LIang Yongsheng and Ran LI1
Abstract
Four strams of Rhyzopertha dommica (F.) (Coleoptera:Bostnchidae ) , 5 strams of Sitophsiu» oryzae (L.)(Coleoptera: Curcuhonidae ) and 4 strains of Cryptolestes[erruqineus (Stepens) (Coleoptera: Cucujidae) resistant tophosphme were tested for cross-resistance to femtrothionand chloropicnn Femtrothion resistance was determmed byusing the impregnated-paper assays (FAO Method No. 15),and chloropicnn resistsnce was tested by fumigation indesiccators The results revealed that phosphine resistantstrains of S. oryzae and C. [erruqmeus had no cross-resistance to chloropicnn or fenitrothion However, twophosphine-resistant strains of R dommica showed someresistance to fenitrothion With resistance factors of 2.94 and5.24. Not all phosphme-resistant strains showed resistanceto fenitrothion, therefore, we concluded that this resistancewas due to previous exposure of insects to otherinsecticides. There was no resistance to chloropicrin in anystrains of R. domuuca, Our results indicated that bothferutrothion and chloropicrin would be SUitablechemicals tobe used in a rotation strategy to manage the development ofresistance in these insect pests.
Introduction
Phosphme resistance m insect pests of stored grain ISbecoming more prevalent and serious world wide (Dyte etal 1983; MIlls 1986; Pnce and MIlls 1988; Rajendran1989; Taylor and Halliday 1986; Bekon et al. 1988; Ansellet al. 1991; Li and Li 1994; Liang 1994). In Chma, highlyresistant strains of Rhyzopertha domuiuxi , Sitophtlusoryzae and Cryptolestes [erruqmeus have been detected mseveral storage wear-houses. Levels of resistance are highenough to cause control faIlures and threaten the continueduse of thIS valuable fumIgant. The Chmese gram mdustryrelIes heavIly on phosphine to control msect pests m storedgram. WhIle alternative treatments are avatlable and somenew fumIgants are bemg developed but none have the
1 Chengdu Gram Storage Research Institute of Internal TradeMmistry 95 Huapmfang Street, Chengdu, Sichuan, P R Chma
combined attribute of phosphine of being easy to use, low mcost and ml or very low residues. Therefore, measures mustbe taken to manage or delay the development of resistance tothis matenal in insect pests. A potentially effectiveresistance management tactic is to reduce selection byalternating use of phosphine With other treatments. TwoChemicals that are already registered for use m Chma andthat could be used m such a rotation scheme are the gramprotectant, femtrothion, and the fumigant, chloropicrin.However, for a rotation strategy to be successful there mustbe no cross-resistance between components of the strategy.Therefore, the current study was undertaken to determinewhether phosphine-resistant strains of R. dominuxi; Soryzae and C ferrugineus were resistant to fenitrotnionand to chloropicrin.
Materials and Methods
Origin of strains
The insect strains used m the experiments had thefollowing origins:R. dominica : S-RD - Phosphme susceptible, from
Levels of resistance to phosphine in these strams weredetermined by using the FAO method. (Anon, 1975).
Culturing methods
The R. domtnica were reared on a mixture consistmg oftwo thirds whole wheat and one third cracked grain. The Soryzae were cultured on whole wheat and the C[erruqineue on mixture of cracked wheat, rolled oats andyeast m a ratio of 5 5 1. S. oryzae were cultured at 25°Cand 70% rh and the R. dominica and C. ferrugineus at30"( and 70 % rho
Fenitrothion bioassays
Adult insects, 1 - 2 weeks after enclosion, were exposedto fenitrothion in impregnated-paper assays as essentiallydescribed in the FAO method (Anon, 1974). A graded seriesof 5 - 7 concentrations of fenitrothion and an untreatedcontrol were prepared m a mixture containing Risella 15 oil,acetone and petroleum ether. There were 40 insects With 3rephcates at each concentration. Fenitrothion concentrationsare expressed as percent (w/v) in non-volatile solvent.
Chloropicrin Bioassays
Adult insects, 1 - 2 weeks after eclosion, were exposed to
chloropicrin m desiccators for 20 hours. A graded series of 5-7 concentrations of chloropicrin and an untreated controlwere prepared by using vanous volumes of chloropicrin(purity 94%). Each desiccator contained 2 rephcates of 50insects The appropriate amount of chloropicrin was apphedWIth a syringe to a piece of filter paper suspended inside thetop of each desiccator. The desiccators were placed inconstant environment With a room temperature at 25°C and70~( rh and each desiccator was stirred using a magneticstirrer After an exposure penod of 20 hours, insects wereremoved from the desiccators and cultured as descnbedabove for 14 days when mortality was counted.
Data analysis
Dosage-mortality data were analysed by using probitanalysis after the methods of Finney (Finney, 1971).Relative potency analysis (Finney, 1971) was used todetermme If test strains showed a significantly differentresponse to a susceptible reference strain, and to calculateresistance factors.
Results and Discussion
Fenitrothion
Three phosphine-resistant strams of R. dominica had alow but statistically significant resistance to fenitrothion(Table 1). However, one phosphme-resistant strain was notresistant to femtrothion. This suggests that the resistancesare independent. The low-level resistance may be due toprevious use of fenitrothion on stored grain or may havedeveloped as a cross- resistance from use of otherorganophosphorous insecticides, for example malathion.
Table 1. The data on the response of the strains of R. dommica to fenitrothion,
Stram PH3 Rf N Slope( ±SE) X2 DF LCso(mg/li ter ) L~(mg/liter) Resistance Factor
The results for S. oryzae (Table 2) were parallel to thosefor R. dominica. Four of five phosphine-resistant strainstested possessed very low resistance to fenitrothion and we
conclude that the resistances are, therefore, likely to beindependent.
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Table 2. The data on the response of strains of the S oryzae to fenitrothion.
Strain PH3 Rf N Slope (± SE) LC;9(rng/h ter ) Resistance FactorDF LCso(mg/lIter)
The data on the response of the strams of C. [erruqineusto femtrothion are given m Table 3. Again, WIthonly 1 of 4phosphine-resistant strams showing a weak resistance to
fenitrothion, It is lukely that these resistances aremdependent
Table 3. The data on the response of strams of the C [erriunneus to ferutrothion
The data on the response of the strains of S. oryzae to resistance to chloropicnn The absence of resistance in twochloropicrin (Table 5) mdicate three of the five phosphine- strains suggests that these resistances to chloropicrin andresistant strams had a very low but statistically sigmficant phosphme are mdependent.
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Table 5. The data on the response of the strains of S. oryzae to chloropicnn.
Stram PH3 Rf N Slope (± SE) X2 DF LCso(rng/h ter ) L~9 (rng/li ter ) Resistance Factor
All four strains of phosphine-resistant of C. [erruqineus suggests that the resistances to chloropicnn areshowed no resistance to chloropicrin (Table 6). This independent
Table 6. The data on the response of the strains of C ferruinneus to chloropicnn.
We used FAD method No. 15 (Anon. 1974) to measure theresponse of insects to fenitrothion. ThISmethod has becomean internationally recognised standard. However becausethere IS no standard method to measure resistance tochloroprcnn we modified FAD Method No 16 (Anon 1975)and developed it for testing phosphine in desiccators. Ourmajor modification was to apply chloropicrin to filter paperrectangles suspended inside the hd of a desiccator Probitanalyses of our results gave constant steep slopes, low clu-square values, and relatively narrow confidence mtervalsTherefore, we are confident that the method is reliable androbust.Several but not all phosphine-resistant strains of both R.
dominuxi and S. oryzae showed some resistance to bothchloropicrin and fenitrothion and one phosphine-resistantstrains of C ferruqineus showed resistance toferutrothion, we have three comments on these resultsFIrstly, because resistance was not present in allphospheme-resistant strains we conclude that theferutrothion and chloropicnn resistances are independent ofphosphine resistance. Secondly, the resistances measured forchloropicrin (Tables 4, 5 and 6 ) were all very low, lessthan 2-fold This suggests that differences in calculated LCsovalues etc. were due to differences m the genetic
background of the various test strains and not to resistance.Similarly, differences in resistance to fenitrothion m Soryzae (Table 2) and C. [ernunneu» (Table 3) are lessthan 2-fold and although statistcially significant may not bebiologically meaningful. However, levels of rsistance tofenitrothion in at least two strains of R. domuuca (Table1) are high enough to be regarded as proven. Thirdly,evidence from the responses of S oryzae strains tofenitrthion (Table 2) and chloropicrin (Table 5) indciatethat there IS no cross-resistance between these twochemicals. Specifically, S. oryzae strains R-A and R-CUwith higher resistance to fenitrothion show no correspondingincrease m tolerance to chloropicnn.FInally, we concluded that both chloropicrin and
ferutrotluon would be appropnate chemicals for use in arotation strategy with phosphme to delay development ofresistance. ThIS IS because resistance to phosphine ISmdependent of resistance to chloropicrin and fenitrothionand, in addition, ferutrothion resistance does not providecross-resistance to chloropicnn.
Acknowledgments
The authors wish to thank Dr. M. Bengston, P. J. Collins andG. J. Daglish for supportmg this paper and giving helpfulcomment on the manuscnpt.
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References
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University Press.u, Y. S. and u, W. Z. 1994. Proceedings of 6thinternational working conference on stored-productptotection, Canberra, Australia.Liang, Q. 1994. Grain Storage 23,3-7. (In Chinese)Mills, K. A. 1986. GASCA seminar on fumigationtechnology in developing countries, TDRI Slough, 18-21.Price, L. A. and Mills, K. A. 1988. J. Stored Prod. Res.24, 51- 59.Raiendran, S. 1989. Pesticide Research Journal 12, 111-115.Taylor, R. W. D and Halliday, D. 1986. Proc. CropProtection Conference. Pests and Diseases, Brighton, UK,607 - 613.
