Water content, weight change, and activity of apterous and alate virginoparous Acyrthosiphon pisum (Harris) (Homoptera: Aphididae)
Changes in weight, water content, and activity of alate and apterous virginoparous Acyrthosiphon pisum (Harris) were observed during development from third instar larvae to mature adults. Apterous aphids gained weight steadily until the 4th day of adulthood, and showed no dramatic changes in activity during this period. The live weights of alate aphids decreased during the 24 h immediately following the final moult, but increased gradually after this lime. The onset of weight loss occurred before the active nonfeeding period during which dispersal would normally lake place. Recommencement of weight gain followed the resumption of feeding. After the adult moult, the water content of alatae expressed as a percentage of live weight decreased for 24 h. whereas that of apterae remained constant. During the next 24 h, the water content of alatae increased to a level slightly below that of apterae. Thereafter, both morphs maintained a constant water content until about the 5th day, when a slight increase was evident. Eighty-five percent of the weight loss of adult alatae is attributable to water loss. It is suggested that dehydration of newly moulted adult alatae is an adaptation to facilitate dispersive flight.