SIZE-DEPENDENT TIMING OF METAMORPHOSIS IN MILKWEED BUGS (ONCOPELTUS) AND ITS LIFE HISTORY IMPLICATIONS

Abstract

The relationship between larval body size (indexed by weight) and the timing of adult metamorphosis was studied in Oncopeltus fasciatus and O. cingulifer cingulifer (Hemiptera: Lygaeidae). Experimental manipulation of nymphal growth showed that metamorphosis does not occur until a critical size is attained. When nymphs do not have access to host plant (Asclepias spp.) seeds and feed on plant tissues, growth is slowed considerably. Under these conditions, size-dependent regulation of development provides a means of delaying metamorphosis until a minimal size is attained. This critical size is greater for the larger species, O. fasciatus, and is also greater for females than males. It probably depends on the initial body size of a nymph at the time it enters the 5th (final) instar.