Host plant exploitation within a population of a generalist herbivore, Choristoneura rosaceana

Feeding performance of larvae of the obliquebanded leafroller, Choristoneura rosaceana (Harris), was estimated on apple and three alternative hosts in the Okanagan Valley. The obliquebanded leafroller is native to the study area and apple was introduced in the valley at the beginning of the century. Components of insect fitness were measured to help formulate predictions about the evolution of host preference in this generalist herbivore. In the summer, females attained a higher pupal weight on apple than on trembling aspen, wild rose and snowberry. Males performed best on apple and trembling aspen. In the field, females arising from caterpillars fed on apple leaves had a 26% greater mean fecundity than if fed on alternative hosts. The diet also affected development time; females initiated pupation later on trembling aspen than on the other hosts. Finally, no differences were found in larval survival nor in the proportion of larvae diapausing when fed on different hosts. These components of fitness indicate apple as the most suitable host in the summer. In the fall, diet influenced larval propensity to initiate diapause in the second or third instar, the time elapsed from hatching to diapause initiation and the weight of the instars initiating diapause. However, no difference in overwintering survival among larvae fed on different hosts was detected. The rank order of water and nitrogen contents of leaves of the host plants did not match the rank order of larval feeding performance in either season. A high suitability of apple and its abundance in the Okanagan valley are factors that would favor the evolution of an increased utilization of this host by the obliquebanded leafroller. 1992 The Netherlands Entomological Society