Generating Baseline Data for Insecticide Resistance: Monitoring in Papaya Mealybug, Paracoccus marginatus (Williams and Granara de Willink)

Acute toxicity studies were conducted on laboratory cultured one day old crawlers and newly emerged adult females of the recently invasive pest of papaya, Paracoccus marginatus (Williams and Granara de Willink) against chlorpyriphos, dimethoate, profenophos, carbofuran, buprofezin, imidacloprid, thiamethoxam and spirotetramat for six generations. The median lethal concentration (LC₅₀) of the test insecticides viz., chlorpyriphos, dimethoate, profenophos, carbofuran, buprofezin, imidacloprid, thiamethoxam and spirotetramat against one day old crawlers in first generation (F₁) were 4.9330, 8.6853, 10.3486, 36.5316, 25.4785, 3.7524, 5.3315 and 5.1747 ppm, respectively, while the corresponding LC₅₀ in the sixth generation (F₆) were 1.8311, 6.6901, 6.4656, 26.7041, 21.9035, 1.7225, 3.6745 and 2.5356 ppm, respectively. Similarly, for adult females, LC₅₀ values were 13.6824, 29.1732, 13.7349, 38.3452, 29.7956, 13.5002, 6.0956 and 8.4333 ppm, respectively in the F₁, while these were 10.0432, 23.2163, 7.9821, 25.2023, 25.0191, 7.9037, 3.8811 and 4.8061 ppm in F₆ generation. The susceptibility index (SI) of F₆ over F₁ generation based on LC₅₀ and LC₉₅ for all the molecules tested was more than one. Based on the present study, tentative discriminating doses (DD) were also fixed based on LC₉₅ obtained in F₆ for adult females.