Factors Influencing the Distribution of a Generalist Spring-Feeding Moth,Operophtera brumata(Lepidoptera: Geometridae), on Host Plants

Abstract

We studied the distribution and abundance of larvae of a highly polyphagous spring-feeding moth, Operophtera brumata (L.), by censusing 16 species of trees and shrubs in a mixed deciduous forest in southeastern Fennoscandia. The survival of 1st instars and the relative growth rate of last instars on potential host plants were studied in the laboratory. Larvae of O. brumata were almost entirely absent from some species of plants in the study area. On the remaining species, which we considered the local hosts of O. brumata, the distribution and abundance of both early and later instars were dependent on the amount of available foliage per shoot. By the later instars, the number of larvae decreased significantly on some hosts that had supported relatively high densities of larvae earlier. Prunus padus (L.) supported the greatest number of larvae in the field, and the survival of neonate larvae and the growth of last instar larvae were highest on this species. The nearly complete avoidance of some tree and shrub species suggests that O. brumata selects hosts but only at a coarse level. Populations of O. brumata in southeastern Fennoscandia appear to be adapted phenologically and physiologically to feed on P. padus. Generalist insect herbivores may frequently adapt to the locally most abundant and suitable host plant. Adaptation to the phenology of one host limits the possibilities for using other hosts and can lead to behavioral and physiological restrictions on host use.