Host plant and habitat effects on behavior, survival, and growth of early instar Dichomeris leuconotella (Lepidoptera: Gelechiidae), leaf-folders on goldenrods

Abstract

The relative success with which caterpillars use different host plant species is determined by a variety of factors including host plant food quality, phenology, morphology, and associated predator loads. These factors vary among habitats, and such variation might account for the restriction of some caterpillar species to particular habitats, when their host plant species are more widespread. I studied the effects of host plant and habitat factors on survival and growth of Dichomeris leuconotella cater- pillars, which occur only in open habitats although their host plants, Solidago and Aster spp., are widely distributed in forest and field. This paper focuses on early instars. In larval transplant experiments, differences between host plant species in both food quality and leaf morphology greatly affected caterpillar performance, but differences between habitats on the same host had unexpectedly minor impact and actually slightly favored performance in forests. On an abundant forest goldenrod, S. caesia, first and second instars had poor growth rates and high mortality, even when protected from predators; but on S. rugosa,which grows in both habitats, unprotected caterpillars grew and survived slightly better in forest than in field, and protected caterpillars performed comparably in the two habitats. Early instars began feeding as quickly on S. caesia from forest as on S. rugosa from either field or forest; and once started, they could fold S. caesia leaves faster than those of S. rugosa from either habitat (especially field). However, they took much longer to find suitable sites to spin refuges on the smooth, obscurely veined leaves of S. caesia; and they abandoned leaf refuges readily on S. caesia. Observations of other leaf-folding caterpillar species suggest that S. caesia is best suited as a host for spring-hatching species whose youngest larvae can find ready-made refuge in the leafy terminal bud available at that time.