Intraspecific variation in induction of feeding preference and performance in a herbivorous mite.

Induction of food preference has often been observed in herbivorous insects. The term is used to indicate preference of individuals for the host plant they have already experienced over one they have not experienced. A typical set-up is one where individuals first feed on host X or Y, and are then offered a choice between host X and Y. This set-up--and hence the body of empirical data--has been criticised for lack of a control treatment to untangle the effects of the separate hosts. In this study, we use a design with a third, unrelated host as control to investigate induction of preference in the herbivorous arthropod, Tetranychus urticae. We provide evidence of induced preference, as well as induced performance, and show that there is considerable variation in these two traits among strains. We suggest induced resistance to toxic secondary plant chemicals as one potential explanation for induced performance. This in itself suggests associative learning as the most likely candidate learning mechanism for induction of preference in this species. Phenotypically plastic effects underlying induced performance may be a general aspect of induction of preference in herbivorous arthropods, which warrants closer attention to these phenomena.