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

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