Stability of the resistance to lambda-cyhalothrin in the ladybird beetle Eriopis connexa

Natural enemies resistant to insecticides are expected to help control the remaining arthropod pests after insecticide application and, hence, prevent crop damage, pest resurgence, and resistance selection. Field-evolved resistance to lambda-cyhalothrin and to other pyrethroids exhibited by the neotropical ladybird beetle Eriopis connexa (Germar) (Coleoptera: Coccinellidae) has been characterized and enhanced under laboratory selection. In this study, we investigated the stability of the resistance and its relationship with detoxification enzyme activity and biological performance, which are important for a biocontrol agent. One subgroup of the resistant population of E. connexa was established without selection pressure (R-UNSEL) during eight generations, and compared to either a susceptible (SUS) or its parental resistant (R-SEL) population. The resistance ratio in R-UNSEL was reduced by 50% compared to R-SEL between the first and fourth generation without selection pressure, but stayed stable afterwards, from the fifth to the eighth generation. Despite eight generations without selection pressure and reduction in the resistance level, the resistance ratio in R-UNSEL was still 39× greater than in the SUS population. The reduced resistance in R-UNSEL correlated to reduction in esterase activity, but the R-UNSEL maintained greater activity than the SUS group. The absence of selection pressure and reduction in enzyme activity in R-UNSEL did not mitigate the adaptive costs, with 2.7× lower egg production compared to SUS females. These findings indicate that resistance to lambda-cyhalothrin in R-UNSEL has already stabilized in the population. Although the resistance ratio and detoxifying enzymes were reduced in R-UNSEL, the impact on fecundity was maintained. Furthermore, the absence of crossing with wild SUS individuals will allow the R-UNSEL offspring to retain the resistance allowing survival to lambda-cyhalothrin even when used at the highest recommended field rate.