Effect of selected neonicotinoids on predatory coccinellids in Bt cotton ecosystem

Abstract

With the introduction of Bt cotton in India during 2002, the production and productivity has increased considerably with the reduction in bollworm complex incidences. But, sucking insect pests became a menace that warranted spraying of chemical insecticides. These insecticides belonging different groups, adversely affected the population of natural enemies like coccinellids that played a vital role in naturally keeping the sucking insect pest population under control. Field studies were conducted in 2 villages viz., Mambattu and Salai in Tamilnadu during the years 2014 and 2015. Five neonicotinoids viz., imidacloprid 17.8 SL, acetamiprid 20 SP, thiacloprid 21.7 SC, thiamethoxam 25 WDG and clothianidin 50 WDG were tested alongside monocrotophos 36 SL and untreated control. At 1, 3, 7 and 14 days after treatment, monocrotophos recorded maximum population reduction of 78.8, 83.5, 70.4 and 62.6% respectively. Among neonicotinoids, clothionidin 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 percentages 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 broad spectrum neonicotinoids like thiacloprid, thiamethoxam and clothianidin and non-selective insecticide like monocrotophos.