INTRINSIC FACTORS CAUSING QUALITATIVE CHANGES IN POPULATIONS OFPORTHETRIA DISPAR(LEPIDOPTERA: LYMANTRIIDAE)

Abstract

Evidence is presented to suggest that the gypsy moth,Porthetria dispar(L.), is numerically self-regulating through a shift in the quality of individuals induced by changes in nutrition. This qualitative change affects dispersal, behavior, developmental rate, and fecundity, and this providesP.disparwith the ability to respond to intrinsic and extrinsic factors faster and more efficiently than if dependent on selection. Adaptability is further facilitated because the change in quality can be induced either in the previous generation by the amount of nutrient reserves provided the eggs, or during the current generation by hunger, crowding, or cool temperature. This change is best characterized by an increase in the number of larvae with additional instars. In these larvae, a prolongation of instar I and a shift in behavior increases their potential for dispersal. The similarities and differences betweenP.disparandMalacosoma pluviale(Dyar) are discussed.