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 ho st species composition may experience selection for divergent host-sel ection behaviour. To assess potential genetic constraints on the evolu tion of host-selection behaviour in such populations, we estimated gen etic 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 usin g the threshold model of quantitative genetics. According to this mode l, there is a continuously distributed variable describing the motivat ional/physiological state of individuals in the population, and a thre shold of acceptance representing the acceptability of a host species. Individuals in which this variable exceeds the threshold accept the ho st while individuals below the threshold reject it. Parent-offspring r egressions, a selection experiment, and comparisons of full-sibs in th ree pairs of populations revealed significant additive genetic variati on in host acceptance. Genetic correlations between the responses to d ifferent hosts were either positive or not significantly different fro m zero, suggesting that local change in host acceptance will not favou r behavioural specialization in populations of C. rosaceana. The patte rn of the reaction norms for host response in the pairs of populations confirmed that divergence in host-selection behaviour does not involv e behavioural specialization in the obliquebanded leafroller.