Evolution of biological control agents following introduction to new environments

The introduction of biological control agents (BCAs) creates the potential for adaptive evolution in translocated organisms. BCAs are confronted with new environments that can promote adaptation to exploit novel resources, even within short ecological time frames. In particular, insect BCAs are amenable to rapid evolution due to their short generation times and relatively large population sizes. These factors hypothetically increase the likelihood that, when exposed to novel habitats, environmental selection could cause BCAs to extend their range to non-target host species. Alternatively, insects may simply extend their range as their generalist or polyphagous habits are fully realized. In this review, we consider recent literature that addresses these topics. Adaptations to environmental conditions have been demonstrated in a number of BCAs. Mechanisms of adaptation include founder effects, hybridization, and endosymbiosis. Yet, there is little evidence of adaptive host range expansions among insect and weed biological control agents to non-target species, albeit existing examples are from limited numbers of studies. Important future directions and current developments in the field incorporate next generation sequencing technology that can promote better resolution of population divergence, possible mechanisms involved in adaptation to novel resources, and insect hybridization. Future studies should also include a careful consideration of the influence of microbes on BCA efficacy and environmental adaptation.