The concept of ecological generalism (or polyphagy) is widely used in ecology to describe and predict aspects of the behaviour of predatory insects, notably with regard to the management of insect pests. The assumptions of ecological generalism have their basis in competition and optimization. We review the historical context and perspectives that led to the development of the concept of ecological generalism as it is applied to diet breadth in predatory insects. We identify how flaws in this concept limit its utility in describing and predicting the behaviour of organisms. We re‐analyse the behavioural expectations of putatively generalist organisms with a focus on the mechanistic aspects of predation; that is, we develop an interpretation based on the adaptations that mediate their responses to particular cues in their environment. This mechanistic analysis emphasizes the need to determine the primary environmental associations of putatively generalist species, and the adaptations that underpin those associations. This approach thus highlights the importance of appropriate matching of predator species to prey species in biological control, based on an understanding of these adaptations and associations. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, ••, ••–••.

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1 The herbivorous bug Heteropsylla cubana Crawford (Homoptera: Psyllidae) is a pest of the cattle fodder crop Leucaena (Leguminosae: Mimosoideae). The interaction between the psyllid and three varieties of its Leucaena host plant was investigated in relation to the apparent resistance of some Leucaena varieties (Leucaena leucocephala, Leucaena pallida and their hybrids) to attack.2 Field trials demonstrated that adult psyllids distinguished among the different varieties of Leucaena over a distance, and were attracted to L. leucocephala in significantly higher numbers than to L. pallida or to the hybrid. Pesticide treatment increased the attractiveness of Leucaena plants, even of those deemed to be psyllid resistant. Numbers of psyllid eggs and nymphs, sampled in the field, reflect the arrival rates of adults at the three plant varieties. 3 Wavelength reflectance data of the three Leucaena varieties were not significantly different from one another, suggesting that psyllids cannot discriminate among the three plants using brightness or wavelength cues. There was a differential release of caryophyllene among the three varieties. Release of caryophyllene in L. leucocephala and the hybrid appeared to be influenced by environmental conditions. 4 Experiments demonstrated that caryophyllene (at least on its own) did not influence the behaviour of leucaena psyllids in relation to leucaena plants. 5 The results suggest that host plant volatiles cannot be dismissed as significant in the interaction between the leucaena psyllid and its Leucaena host plants.Further avenues for investigation are recommended and these are related to novel ways of understanding resistance in insect plant inter-relationships.

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