Beyond biological control: non-pest insects and their pathogens in a changing world

Over the last few decades, there have been considerable advances in the fields of insect pathology and insect conservation but the two disciplines rarely meet. The potential of entomopathogens as biological control agents of pest insects is widely recognised but information on the role of pathogens in insect population regulation, more generally, is limited. For example, the role of pathogens as natural enemies of non-pest insects, including those of conservation value, is seldom considered beyond their context as 'non-targets' of microbial control agents. Entomopathogens are prevalent in natural systems and should receive greater attention in life-history studies. There is no doubt that viruses, bacteria and fungi are major mortality agents of insects but their significance tends to be overshadowed by the attention given to predators and parasitoids. We highlight the critical function that entomopathogens could have in insect population dynamics with particular reference fragmented habitats as illustrated by the theoretical literature. However, we emphasise that there are few empirical studies to test theoretical predictions. We suggest that since an increase in the incidence of disease is predicted in most environmental change scenarios, it is more important than ever to turn our attention to insect pathology when we consider insect population dynamics.