Risks of interbreeding between species used in biological control and native species, and methods for evaluating their occurrence and impact.

Abstract

Insect species introduced or augmented for biological control of insect pests may interbreed with native species, which may change fitness or cause evolution, which may in turn alter abundances. By 'interbreeding', we mean any reproductive interactions between species. We review the literature on factors affecting the likelihood of interbreeding between insect species and the impacts when these occur. We discuss phylogenetic relatedness, geographical distribution, spatial and temporal barriers to mating, mate recognition, copulation and sperm use, hybrid inviability and sterility, hybrid speciation, reproductive character displacement and introgression. We concentrate on the risks from introduced species, but we also address the risks from augmentation of native species. We propose methods for pre-introduction or pre-augmentation assessment of the likelihood and potential impact of interbreeding between native species and insects used in biological control. Finally, we propose methods for evaluating the occurrence and impact of interbreeding after insect species are introduced or augmented.