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

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Spring 2003 Resistant Pest Management Newsletter Vol. 12, <strong>No.2</strong>laboratory 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
Spring 2003 Resistant Pest Management Newsletter Vol. 12, <strong>No.2</strong>Madurai (3.4) followed byKovilpatti (4.1) and Coimbatore(4.7) (Table 2).Quinalphos: Maximum resistance toquinalphos was observed in theNalgonda population (20.937µg/µL)followed by the Guntur population(12.564 µg/µL). Least resistancewas noticed in the Maduraipopulation (0.5 µg/µL). Highresistance to quinalphos wasrecorded by the population fromNalgonda (123.2 fold) followed bythe Guntur population (73.9 fold) asagainst the susceptible ICRISATpopulation (Table 3).Chlorpyriphos: Maximumresistance to chlorpyriphos wasrecorded in Guntur (11.038 µg/µL)followed by Nalgonda (9.480µg/µL). Minimum resistance wasobserved in the Madurai population(0.36 µg/µL) followed by theKovilpatti population (0.463) andCoimbatore (1.128). The resistanceratio against the ICRISATsusceptible strain was found to behighest for the population of Guntur(78.8 folds) followed by Nalgonda(67.7) and Dharwad (33.4). Theleast ratio was recorded in thepopulation from Madurai (2.6) andKovilpatti (3.3) (Table 4).Kovilpatti (0906) and Coimbatore (1.025). Theresistance ratio (RR) against the ICRISAT susceptiblestrain was found to be highest for the population ofNalgonda (60.2 fold) followed by Guntur (45.7). Theleast resistance ratio was observed in the population ofCypermethrin: The Raichurpopulation recorded a maximumLD50 value to cypermethrin (22.40µg/µL) followed by the populationfrom Guntur (10.92) and Nalgonda(9.984). The lowest LD50 value wasobserved in the population fromMadurai (0.143µg/µL) followed byKovilpatti (0.192) and Coimbatore(2.472). The resistance ratio (RR)against the ICRISAT susceptiblestrain was found to be highest forthe population of Raichur (379.7fold) followed by Guntur (185.0)and Nalgonda (169.2). The leastresistance ratio was observed in thepopulation of Madurai (2.4) followed by Kovilpatti(3.3) (Table 5).Carbaryl: The Raichur population recorded amaximum LD50 value to carbaryl (13.36 µg/µL)15
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Vol.12_No.2 - Pesticide Alternatives Lab - Michigan State University

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