Effect of selected neonicotinoids on predatory coccinellids in Bt cotton ecosystem .

Field studies were conducted in two villages viz., Mambattu and Salai in Tamil Nadu to assess the toxicity of five neonicotinoids viz., imidacloprid 17.8 SL, acetamiprid 20 SP, thiacloprid 21.7 SC, thiamethoxam 25 WDG and clothianidin 50 WDG to coccinellid predators in Bt cotton. At 1, 3, 7 and 14 days after treatment, standard check monocrotophos recorded maximum reduction of 78.8, 83.5, 70.4 and 62.6% respectively. Among neonicotinoids, clothianidin was found to be comparatively more toxic to coccinellids, followed by thiamethoxam and thiacloprid. Acetamiprid was found to be safest among chemical treatments with population reduction of 45.6, 53.9, 36.5 and 24.7% respectively at 1, 3, 7 and 14 days after treatment followed by imidacloprid and thiacloprid. Two rounds of spray of neonicotinoids on Bt cotton had significant impact on the coccinellids, when compared with untreated control plots. However, monocrotophos recorded relatively lowest population of coccinellids compared to untreated control and neonicotinoids. With significant population built-up after 7 days after acetamiprid and imidacloprid sprays, the 2 neonicotinoids may be suitable candidates for inclusion in integrated pest management of sucking insect pests in major Bt cotton growing areas as these insecticides are comparatively less toxic to predators as compared to other neonicotinoids like thiacloprid, thiamethoxam and clothianidin and non-selective insecticide like monocrotophos.