Maternal effects in an insect herbivore as a mechanism to adapt to host plant phenology

P>1. Maternal effects may play an important role in shaping the life history of organisms. Using an insect herbivore, the winter moth (Operophtera brumata) feeding on oak (Quercus robur), we show that maternal effects can affect seasonal timing of egg hatching in an herbivore in an adaptive way.

2. Winter moth egg-hatching needs to coincide with oak bud opening, as only freshly emerged leaves are suitable as food for the caterpillars. However, there is spatial variation in the timing of bud opening among oaks to which the winter moth needs to adapt.

3. We show experimentally that the generation time between the mother's and her offsprings' hatching dates was shorter for mothers who hatched late relative to bud opening of the tree they had to feed on (and hence had to feed on older leaves) than for mothers' who hatched on time. Maternal feeding conditions affected both the larval and the pupal development time of the mother as well as the egg development time of her offspring: at all three stages developmental time was shorter for the mistimed treatment.

4. We thus show that adaptation to spatial variation may be achieved via maternal effects. While this is a mechanism selected to adapt to spatial variation, it may now also play a role in adaptation to climate change induced shifts in host phenology, and allow insect herbivores to adapt to changes in the seasonal timing of their food availability without the need for genetic change.