Comparative Growth Energetics of a Migratory and Nonmigratory Insect: The Milkweed Bugs

Abstract

The energetics of nymphal development of a migratory milkweed bug, Oncopeltus fasciatus, were compared to those of an overwintering resident milkweed bug, Lygaeus kalmii, at temperature and light conditions representative of midsummer (30.degree. C, 14[light]L:10[dark]D and early autumn (20.degree. C, 12L:12D). On a milkweed seed diet, both species grew rapidly at 30.degree. C (< 18 days to teneral moult) due to their high assimilation efficiency, 59-93%, and very high net production efficiency, 90-94%. Development of both species was slowed markedly at 20.degree. C (up to 28 days to teneral molt), but low temperatures caused a greater reduction in the overall growth rate of L. kalmii nymphs, 52% of that measured at 30.degree. C, than of 0. fasciatus nymphs, 71% of that measured at 30.degree. C. Certain characteristics of development were consistent with a migratory habit: the migrant grew more rapidly than the resident by maintaining a higher assimilation efficiency on its seasonally available and more monophagous diet; and the migrant maintained a high growth rate over a broader temperature range thus allowing rapid maturation of nymphs in hot midsummer conditions and the cool fall temperatures occurring prior to migration.