Nonparametric Estimation of Interspecific Spatio-Temporal Niche Separation Between Two Lady Beetles (Coleoptera: Coccinellidae) in Bt Cotton Fields

Abstract

Predaceous lady beetles are important natural enemies of many insect pests in agro-ecosystem. The altered agricultural practices associated with widespread adoption of Bt cotton may have potential effects on the spatio-temporal patterns of predaceous lady beetles, as the composition and abundance of nontarget sucking pests have been changed in Bt cotton fields. In the current study, the spatio-temporal patterns of two important lady beetles, Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae) and Propylea japonica (Thunberg) (Coleoptera: Coccinellidae), were surveyed in Bt cotton fields. A nonparametric method associated with Monte Carlo tests was used to address and test whether niche segregation occurred between H. axyridis and P. japonica. The results showed that the dominant region occupied by P. japonica was toward northeast across the season, whereas H. axyridis had higher presence to the southwest. The temporal patterns of H. axyridis and P. japonica also differed significantly, and the highest levels of each species occurred in different locations from each other on each sampling date in the same Bt cotton fields. In total, there were strong spatio-temporal separation patterns between these two species in Bt cotton fields. These spatio-temporal patterns may produce complementary impacts on prey, and this in turn could be used to strengthen the biological control of insect pests by these two lady beetles.