EVOLUTION OF HOST-SELECTION BEHAVIOR IN INSECT HERBIVORES - GENETIC-VARIATION AND COVARIATION IN HOST ACCEPTANCE WITHIN AND BETWEEN POPULATIONS OF CHORISTONEURA-ROSACEANA (FAMILY, TORTRICIDAE), THE OBLIQUEBANDED LEADFOLLER

Populations of insect herbivores exploiting habitats that differ in host species composition may experience selection for divergent host-selection behaviour. To assess potential genetic constraints on the evolution of host-selection behaviour in such populations, we estimated genetic variation and covariation in larval acceptance of different host species within and between populations of the obliquebanded leafroller, Choristoneura rosaceana. Host-acceptance behaviour was analysed using the threshold model of quantitative genetics. According to this model, there is a continuously distributed variable describing the motivational/physiological state of individuals in the population, and a threshold of acceptance representing the acceptability of a host species. Individuals in which this variable exceeds the threshold accept the host while individuals below the threshold reject it. Parent-offspring regressions, a selection experiment, and comparisons of full-sibs in three pairs of populations revealed significant additive genetic variation in host acceptance. Genetic correlations between the responses to different hosts were either positive or not significantly different from zero, suggesting that local change in host acceptance will not favour behavioural specialization in populations of C. rosaceana. The pattern of the reaction norms for host response in the pairs of populations confirmed that divergence in host-selection behaviour does not involve behavioural specialization in the obliquebanded leafroller.