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

Spring 2003 Resistant Pest Management Newsletter Vol. 12, No.2laboratory on a semi-synthetic diet toget F1 homogeneous larvae forbioassays.Larvae of 30-40 mg were used forbioassays. Six insecticides viz.,monocrotophos, chlorpyriphos,Endosulfan, carbaryl, cypermethrin,and quinalphos that are extensivelyused to control bollworm in cottonecosystems of South India were usedto determine baseline resistance. Thetechnical grade chemicals of theseinsecticides were obtained from M/SDe Nocil Crop Protection Ltd., M/SSyngenta Company, and M/S AventisCrop Science. Differentconcentrations of these selectiveinsecticides were prepared inanalytical grade acetone and aHamilton microapplicator was used todeliver a 1.0 µl drop to the thoracicdorsum of each third instar larva. Thecontrol larvae were treated withacetone alone. The concentrations ofeach insecticide were varied to obtain20-80 % mortality. Immediately afterexpose to insecticide/acetone, each of30 larvae (for each insecticide) waskept individually in a 30 ml plasticcup with fresh artificial diet andmortality was assessed 72hr aftertreatment. The dose-mortalityregression was computed by usingMLP 3.08 software (Ross, 1987).Monocrotophos: The Nagpurpopulation recorded a maximumLD50 value to monocrotophos(13.690 µg/µL) followed by thepopulation from Nalgonda (7.291µg/µL), Nanded (7.275), Guntur(7.027), Mysore (6.12), and Dharwad(4.22). The lowest LD50 value wasobserved in the population fromKovilpatti (0.308) followed byMadurai (0.452 µg/µL) andCoimbatore (0.777). The resistanceratio (RR) against the ICRISATsusceptible strain was found to behighest for the population of Nagpur(68.5 fold) followed by Nalgonda(36.5), Nanded (36.4), Guntur (35.1),Mysore (30.6), and Dharwad (21.1).The least resistance ratio was observed in thepopulation of Kovilpatti (1.5) followed by Madurai(2.3) and Madhira (3.9) (Table 1).Endosulfan: The Nalgonda population recorded amaximum LD50 value to endosulfan (13.240 µg/µL)followed by the population from Guntur (13.155µg/µL). The lowest LD50 value was observed in thepopulation from Madurai (0740 µg/µL) followed by14