Experiments with <i>Lymantria dispar</i> larvae do not support the idea of physiological adjustment to host individuals by insect herbivores

All organisms have to cope with spatial and temporal heterogeneity of the environment. At short temporal and small spatial scales, organisms may respond by behavioural or physiological mechanisms. To test for physiological adjustments to variation in host quality among tree individuals within a host species, we performed a transfer experiment in a climate chamber using larvae of the polyphagous gypsy moth (Lymantria dispar). We reared larvae for two weeks on leaves of one of three Quercus robur individuals. We found differences in the growth rate of larvae across the host individuals, which indicate that the oak individuals differed in their quality. Furthermore, families of larvae varied in their growth rate and there was variation among the families of gypsy moth larvae in response to leaves from the different oak individuals. After two weeks we offered larvae either leaves of the same or a different individual of the three oaks. We found no effect of transferring larvae to a different tree individual. The results thus do not support the idea of physiological adjustment of a generalist insect herbivore to variation in leaf quality among host individuals.