Growth and development of a generalist insect herbivore, Operophtera brumata, on original and alternative host plants

A generalist feeding strategy is common among eruptive insect herbivores bu t the ultimate reasons for a generalist strategy are not clear. Although ge neralist insect herbivores are able to complete their life cycle on several species of host plants, there is wide variation in the performance of indi viduals grown on different hosts. We examined whether different populations of Operophtera brumata are adapted to use the host species which is locall y most abundant, and how the host plant affects growth and development of t he insect. We reared two allopatric populations (eastern Finland, Prunus pa dus; south-west Finland, Quercus robur) on four species of host plants (Pr. padus, Populus tremula, Q. robur, Salix phylicifolia) from neonate larvae to the adult stage and measured the growth and development of individuals a nd the timing of adult hatching. The performance of both populations was be st on Pr. padus, and the south-western population, originally on Q. robur, was well adapted to this host. The host affected the growth of females more than that of males. The host plant had an unexpected effect on hatching ti mes of the adults. Individuals grown on the original host hatched in normal synchrony, i.e. males 6-7 days before females; but on alternative hosts th is synchrony was disturbed. As is common in eruptive, capital-breeding gene ralist moths where female fecundity is linked to weight, host quality is cr itical for the flightless females of O. brumata. We suggest that in a heter ogeneous environment the disturbing effect of alternative host plants on ad ult emergence may decrease the population density and growth rate compared to the potential maximum in a homogeneous environment.