author(s)
K Swapna Rani and Anjumoni Devee

abstract
Transverse and zigzag ladybird beetles, Coccinella transversalis Fabricius and Cheilomenes sexmaculata (Fabricius) are dominant aphidophagous predators in agricultural ecosystems. The imidacloprid is an insecticide that belongs to the neonicotinoid group which is used for controlling aphids and other sap feeding insect pests, however, it is found to have certain harmful effects on beneficial arthropods. Hence, there is need to analyse the adverse effects of insecticides on beneficial insects to further improve IPM strategies against crop pests. Therefore, the lethal and sublethal effects of imidacloprid on predatory C. transversalis and C. sexmaculata were tested. The study revealed that the LC₅₀ values of imidacloprid against C. transversalis and C. sexmaculata were 0.02 and 0.06% respectively, which were greater than recommended concentration indicating the less susceptibility of the coccinellids to the insecticide. Residual contact tests were conducted at sublethal doses of insecticide to evaluate the side-effects of these predators starting from the third instars but covering the entire life cycle. Results demonstrated that imidacloprid did not have any significant effects on the developmental time of third instars and adult pre-oviposition period. However there was significant reduction in mating period, oviposition period, fecundity and adult longevity whereas there was significant prolongation of egg incubation period, fourth instar duration and pupal period which ultimately resulted in delay of life cycle when the C. transversalis and C. sexmaculata were exposed at lethal and sublethal doses of imidacloprid. Thus, the study unfolded that imidacloprid at lethal and sublethal concentrations has the potential to affect predatory coccinellids adversely.