Response of different populations of seven lady beetle species to lambda-cyhalothrin with record of resistance.

Simultaneous use of biological and chemical controls is a valued and historic goal of integrated pest management, but has rarely been achieved. One explanation for this failure may be the inadequate documentation of field populations of natural enemies for insecticide tolerance or resistance because natural enemies surviving insecticide application do not create problems like resistant pest species. Therefore, this study investigated 31 populations of lady beetles (Coleoptera: Coccinellidae) regarding their susceptibility to lambda-cyhalothrin, a pyrethroid insecticide that is widely used in cotton and other crops to control lepidopteran and coleopteran pests that are not targeted as prey by lady beetles. The study focused on seven coccinellid species common in cotton fields Coleomegilla maculata De Geer, Cycloneda sanguinea (L.), Eriopis connexa Germar, Harmonia axyridis (Pallas), Hippodamia convergens Guérin-Méneville, Olla v-nigrum (Mulsant), and Brumoides foudrasi (Mulsant) and one lady beetle species [Curinus coeruleus Mulsant] from a non-cotton ecosystem for comparisons. Dose-mortality curves were estimated after topical treatment of adult lady beetles with lambda-cyhalothrin. Statistically significant variations in lady beetle susceptibility were observed between species and between populations of a given species. Seven and eighteen populations of lady beetles exhibited greater values of LD50 and LD90, respectively, than the highest recommended field rate of lambda-cyhalothrin (20g a.i./hectare≈0.2g a.i./L) for cotton fields in Brazil. Furthermore, based on LD50 values, 29 out of 30 tested populations of lady beetles exhibited ratios of relative tolerance varying from 2- to 215-fold compared to the toxicity of lambda-cyhalothrin to the boll weevil, Anthonomus grandis Boh. (Coleoptera: Curculionidae). Four populations of E. connexa were 10.5-37.7 times more tolerant than the most susceptible population and thus were considered to be resistant to lambda-cyhalothrin, the first record of resistance for this species. These findings demonstrate that field selection for resistance to lambda-cyhalothrin in common lady beetles is occurring, opening up possibilities to effectively integrate biological control where the popular insecticide lambda-cyhalothrin is used.