Vol.12_No.2 - Pesticide Alternatives Lab - Michigan State University

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Spring 2003 Resistant Pest Management Newsletter Vol. 12, No.2REFERENCESAbbott, W. S. 1925. A method of computing the effectiveness of aninsecticide. J. Econ. Entomol., 18: 265-267.Busvine, J.R. 1980. Recommended methods for detection andmeasurement of resistance of agricultural pests to pesticides. FAO,Rome. pp. 44-46.Finney, D.J. 1971. Probit analysis. Third Edition. S.Chand & Co.Ltd.,New Delhi.333 p. Georghiou, G.P. 1981. The occurrence ofresistance to Pesticides in arthropods. An index of cases reportedthrough 1980. FAO, Rome. 373 p.Mascarenhas, R.N. and Boethal, D.J. 1997. Responses of field collectedstrains of soybean looper (Lepidoptera: Noctuidae) to selectedinsecticides using an artificial diet overlay bioassay. J.Econ.Entomol., 90: 1117-1124.Salgado, V.L., Watson, G.B. and Sheets, J.B. 1997.Studies on the modeof action of spinosad, the active ingredient in Tracer Insect Control.Proc. Beltwide Cotton Production Conferences. Memphis, TN,USA. pp. 1082-1086.Sparks,T.C., Thompson, G.D., Herbert, A.K., Hertlein, M.B., Larson,L.L., Worden, T.V. and Thibault, S.T.1998. Biological activity ofthe spinosyns, new fermentation derived insect control agents ontobacco bud worm (Lepidoptera: Noctuidae) larvae. J.Econ.Entomol., 91: 1277-1283.Sparks, T.C., Crouse, G. D. and Durst, G. 2001. Natural products asinsecticides: the biology, biochemistry and quantitative structureactivityrelationships of spinosyns and spinosoids. PestManagement Sc. 57: 896-905.R.K.AroraDivision of EntomologyFaculty of Agriculture, SKUAST-JammuUdheywalla Jammu -180 002IndiaBaseline Susceptibility of Diamondback Moth, Plutella xylostella (Linn.), to New InsecticidesABSTRACT Toxicity of three new insecticides (fipronil,indoxacarb, and diafenthiuron) was assessed against3rd instar larvae of diamondback moth (DBM) using aleaf residue technique. LC50 values of theseinsecticides were observed to be very low indicatingthe high toxicity and potential of these compoundsagainst multi-resistant populations of DBM. Baselinesusceptibility data will be useful to monitor theresponse of DBM to these compounds in future forearly detection of resistance.KEY WORDS Diamondback moth, cabbage, newinsecticides, bioassay, insecticide resistance, baselinesusceptibilityand Joia, 1992). The problem is acute in areas wherevegetables are grown extensively in a staggeredmanner almost throughout the year, particularly aroundand near big cities (Joia et al. 1996). In view of thereports of field control failure and the development ofresistance in the pest, it was considered appropriate toundertake studies to assess toxicity of new moleculestowards multi-resistant populations of DBM. Theobjective was to identify potential compounds forinsecticide resistance management of the pest and toestablish baseline susceptibility of DBM to theseinsecticides.MATERIALS and METHODSINTRODUCTION Large scale and indiscriminate use ofinsecticides for the control of insect pests, necessitatedby ever increasing demand for quality food and betterpublic health has resulted in a number of problems.One of the major problems that has arisen out of theabuse of insecticides is the development of resistancein insect pests to pest control chemicals. Diamondbackmoth (DBM), Plutella xylostella (Linn.), is aubiquitous pest wherever crucifers are grown. It is themost destructive and is a regular pest of cabbage andcauliflower. The pest is known for its propensitytowards quick development of resistance (Georghiou,1990) and there have been instances when this pest hasdeveloped resistance to a new molecule within a fewyears of its introduction (Hama, 1989). The pest hasdeveloped resistance to almost all the recommendedinsecticides belonging to major groups in many parts ofthe world (Talekar and Shelton, 1993) and is becomingincreasingly difficult to control. In India, resistance inP. xylostella to different insecticides has been reportedfrom several states like Punjab, Haryana, UttarPradesh, Karnatka, Tamil Naidu, and Andhra Pradesh(Mehrotra and Phokela 2000). In Punjab, DBM hasdeveloped resistance to quinalphos, fenvalerate,cypermethrin, and several other insecticides (ChawlaTest Insects: Pupae and larvae of diamondbackmoth were collected from infested plants in variouscabbage / cauliflower growing areas of Punjab duringthe period from September to October. The insectswere reared in the laboratory on cabbage leavesobtained from unsprayed crops. Third instar larvae ofuniform size and weight from F1or subsequentgenerations were used for bioassay.Insecticides: Commercial formulations of testinsecticides were procured from the manufacturersdirectly. The products were diluted with water to obtaina range of test concentrations, usually 6 to 7 for each ofthe test insecticides.Bioassay Method: The leaf residue technique(Tabashnik et al., 1987) with slight modifications wasused for exposing larvae to test insecticides. Discs (5cm diameter) of cabbage leaves were dipped in testconcentrations for 5 seconds and dried for 1 hour atroom temperature. Distilled water was used as control.After drying, the discs were placed in glass containers.Around thirty 3rd instar larvae were released per twodiscs for each concentration and the mouth of thecontainer was secured with muslin cloth tied with30
Spring 2003 Resistant Pest Management Newsletter Vol. 12, No.2rubber band. The test larvae were allowed to feed for48 hours on treated discs. Thereafter, larval mortalitywas recorded and LC 50 worked out using a computerprogram based on Probit Analysis (Finney, 1971).RESULTS and DISCUSSIONFipronil: Fipronil, 5-amino-3-cyano-1-(2,6-dichloro-4-trifluoromethylphenyl)-4-(trifluorosulfoxide-1,2-pyrazole), is an insecticide of recent introduction. Thisinsecticide was evaluated in the laboratory for itstoxicity towards DBM larvae. Fipronil proved to bevery toxic to test larvae. The LC50 values of fipronilagainst six populations of DBM ranged from 0.0001 to0.0045% (Table 1). The population from Khanna wasthe most susceptible, and that from Amritsar was theleast susceptible to this insecticide. Low LC50 valuesindicate high toxicity of fipronil to multi-resistantpopulations of DBM. Non-exposure of the pestpopulations to this compound and high inherenttoxicity may be the possible reasons for low LC50values. Low LC50 values (3.17 µg/ml) of fipronil havebeen reported in diet bioassay with DBM larvae(Argentine et al., 2002). The compound has beenreported to be effective against DBM in China (Zhao etal. 1995) and Hawaii (Mau and Gusukuma-Minuta,1999). It has also been registered for the pest oncauliflower in Western Australia (Lancaster and Burt,2001).to DBM larvae from four different populations and theLC50 values and other probit parameters are presentedin Table 3. These data show that this insecticide alsopossesses fairly high toxicity to resistant DBMpopulations but it is not as toxic as previouslydescribed fipronil and indoxacarb. The LC50 valuesvaried from 0.0051 to 0.011%. Zhao et al. (1995) havereported diafenthiuron to be effective against DBM inChina. Solang and Sribhuddachart (2002) havereported that in addition to its high toxicity to DBM,the pest did not develop resistance after selection with25 generations.All of these compounds have been introducedrecently and are still at the evaluation stage underIndian conditions. Apart from inherent toxicity of theseinsecticides, non-exposure of DBM populations tothese chemicals is perhaps the other reason for verylow LC50 values. After further testing, theseinsecticides may prove as alternate control measuresfor DBM in problematic areas. However, to fullyrealize their potential and to increase useful life forlong-term use in effective IRM, these and similar newgeneration compounds will have to be used veryjudiciously. There must be some mechanism toIndoxacarb: Indoxacarb, (S)-methyl-7-chloro-2,5-dihydro-2 [[(methoxycarbonyl) [4-(trifluoromethoxy)phenyl] amino] carbonyl]-indeno{1,2-e}{1,3,4}oxadiazine-4a(3H)-carboxylate, is another newinsecticide, which has been specifically introduced forthe control of lepidopterous insect pests. Bioassaystudies with indoxacarb were also conducted againstmulti-resistant populations of the pest from Jagraon,Samrala, Phagwara, and Khanna and the results aregiven in Table 2. This insecticide was found to beextremely toxic and the LC50 values of this compoundranged from 0.00003 to 0.00007%. Very high toxicityof this insecticide against DBM larvae indicates thehigh potential of indoxacarb. Field trials conducted atthe University of Arizona have shown it to give goodcontrol of DBM infesting cabbage (Umeda et al. 2000).It has also been reported to exhibit synergism withgranulosis virus against DBM (Krishnamoorthy 2002).Mau and Gusukuma-Minuta, (2002) have reported itsuse in insecticide resistance management of DBMHawaii.Diafenthiuron: Another introduction of recent times,diafenthiuron, 3-(2,6-diisopropyl-4-phenoxyphenyl)-1-tert-butyl-thiourea, is a new type of thiourea. It is apro-insecticide. After application, it gets converted tocarbodiimide, which is an inhibitor of mitochondrialATPase. This compound was also tested for its toxicity31
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