Variability for host preference in insect populations: Mechanistic and evolutionary models

Two models that explain variation in behaviour associated with locating and accepting different habitats (host plants) are described and analyzed. One model describes the dynamics of search-mode ontogeny in Battus philenor butterflies. This model predicts that the proportion of females using either of two search modes at any given time reflects an equilibrium between the rate at which females switch from using a narrow-leaf search mode to using a broad-leaf search mode and the rate at which the opposite switch is made. Preliminary data suggest that the model predicts reasonably well the observed seasonal change in predominant search mode in the field. The second model, really a set of related models, describes the dynamics of genes that influence searching behaviour. Several predictions of these models are: (1) gentic variation for proportional allocation of offspring to different habitats should be more common under soft-selection regimes than under hard-selection regimes. (2) Polyphagy should be more common under soft selection than under hard selection. (3) Whether changes in the relative abundances or relative quality of different habitats lead to evolutionary change in apportionment of offspring to habitats depends in a complex way on mode of population regulation, method of search, type of limitation of fecundity and genetic properties of loci affecting preference. Although the two types of models superficially appear to address different types of behavioural variation, they may be used in a complementary fashion to understand the evolution of habitat selection behaviour.