Environmentally-based maternal effects: a hidden force in insect population dynamics?

The nutritional environment of the parental generation of the polyphagous gypsy moth, Lymantria dispar, can significantly influence the growth and reproductive potential of the next generation through environmentally-based maternal effects. In the first experiment, members of the parental generation were reared on red oak trees (Quercus rubra L.) with known defoliation and phenolic levels. Diet in the offspring generation was homogeneous (synthetic diet). With genetic effects accounted for 1) offspring attained greater pupal weights when their mothers fed on trees with higher leaf damage levels, 2) daughters had a shorter prefeeding stage, a trait associated with dispersal tendency, when their mothers experienced higher condensed tannin levels, and 3) sons had lower pupal weights when their mothers experienced greater condensed tannin levels. In the second experiment, members of the parental generation were reared on either red or black oak (Q. velutina) trees. Offspring of each mother were divided among four diets: red oak, chestnut oak (Q. prinus L.), a standard synthetic diet, and a low-protein synthetic diet. The parental host species accounted for 24% of the variation in daughters' development time; offspring diet accounted for 52%. When mothers were reared on black oak rather than red oak, their offspring developed significantly faster when the F1 diet was chestnut oak. Environmentally-based maternal effects can significantly influence the expression of offspring dispersal potential, growth rate, and offspring fecundity. These traits contribute to natality and survival in natural populations and, hence, to population growth potential. Theoretical models of insect population dynamics demonstrate that the presence of a time delay in a density dependent response can induce destabilization. Maternal effects act on a time delay and may participate in the destabilization characteristic of outbreak species.