Empirical and experimental evidence of phenotypic plasticity to soil moisture conditions in the invasive cactus moth, Cactoblastis cactorum (Pyralidae)

Abstract

Since the cactus moth (Cactoblastis cactorum) was released in several continents for biological control of prickly pear cactus (Opuntia spp.), it has become invasive, particularly in the Caribbean and Southern North America threatening native Opuntia species. Recent niche ecological modelling suggests that topsoil moisture conditions experienced by the pupae can significantly determine the presence of the moth. In this study we described the range of topsoil moisture content across invaded and native populations and performed a reciprocal rearing experiment using native populations with extreme soil moisture conditions to provide evidence of local adaptation of the source population from which the initial individuals were collected for biological control campaigns in 1924. Throughout several decades, the moth has established under a wider range of topsoil moisture content than that registered within the native range in South America. This suggests that the moth has expanded its tolerance to topsoil moisture conditions, or that it already had enough phenotypic plasticity. Experimental results supported this last explanation since no evidence of local adaptation was detected. Thus, future forecasts of the invasion dynamic in non-native regions should incorporate these results to improve the model prediction and control practices.