Life history perspectives on pest insects: What’s the use?

In his seminal 1954 paper on the ‘population consequences of life history phenomena’, Cole noted that ‘these computations may have practical value in dealing with valuable or noxious species’. In the present paper, the question is asked: ‘is research based on evolutionary perspectives in general, and life history theory specifically, really useful for dealing with insect pests?’ Perhaps such theory-based research is rather a luxury: time and resources would be better spent on entirely applied aspects of the problem. The conclusion of the present discussion is that having an evolutionary perspective guiding research is actually a very cost-effective way of dealing with applied problems, as it provides a clear basis for interpretations, generalizations and predictions. Life history theory is a very central and necessary part of both population ecology and general evolutionary theory, and its specific usefulness in pest forecasting and management are discussed. Nevertheless, our ability to predict insect population dynamics is still limited, and so is our ability to make use of an insect’s life history traits to predict its propensity to become a pest. I suggest that the former shortcoming is largely due to poor understanding of insect life history plasticity. This, in turn, may partly be due to a paucity of studies where reaction norms are investigated as putative adaptations. I suggest that the latter shortcoming is due to problems inherent with studying life history traits as adaptations, for example the lack of an independent fitness model and the fact that life histories tend to form syndromes of coadapted traits. These points are illustrated with examples from my own work on non-pest butterflies and from insect–Eucalyptus systems.