Cost of Flight Apparatus and Optimum Body Size of Aphid Migrants

Abstract

The incorporation of aerodynamic considerations into an optimal energy partitioning model developed for aphids results in the prediction that migrants should be smaller and take longer to develop than nonmigrants. If individuals are structurally similar (i.e., the relative sizes of body parts and flight apparatus are similar), then both within and between species, aerodynamic considerations predict that biomass of wing muscles should scale relative to body mass with an exponent between 1 and 7/6, and wing beat frequency directly proportional to wing length for maximum power output to 1/2 power of wing length, when cruising. The empirical results for aphids indicate that within species, individuals of different sizes may not be structurally identical; large individuals appear to have proportionally smaller wings, and as theory predicts, appear to compensate for this by having proportionally larger wing muscles than small individuals. Interspecifically, aphids appear to be structurally identical both in terms of wing area, wing beat frequency, and in the relative size of the thorax. As predicted both intra-and interspecifically, large migrants, although having larger gonads, nevertheless have proportionally smaller gonads than small migrants. Empirical results also conform to the prediction that migrants should be smaller than nonmigrants, particularly so in large species. The prediction that the developmental time for migrants should be longer than for nonmigrants is supported by published data for aphids. The significance of these findings is discussed in the context of Roff's hypothesis that insect migrants should be larger and develop faster than nonmigrants.

Gene Expression Profiling in Winged and Wingless Cotton Aphids, Aphis gossypii (Hemiptera: Aphididae)

“…Our results suggest that sugar or glycogen metabolism is faster in wingless morphs and those carbohydrates were used for development and production. This is consistent with the contention that sugar and glycogen is not the fuel of aphids for migration 51.…”

The cabbage aphid: a walking mustard oil bomb

“…This investment is likely to be particularly worthwhile for wingless aphids, which are committed to a sedentary life and a limited ability to escape predation via dispersal. However, for winged aphids, the development of the flight apparatus also involves substantial energetic costs (Dixon & Kindlmann 1999). During the last few days of nymphal development, winged aphids show a rapid increase in synthesis and storage of lipid reserves, attaining a lipid content of up to 50% dry weight (Liquido & Irwin 1986).…”

Xylem ingestion by winged aphids

“…Recently-moulted apterous virginoparae also showed frequent labial contact with the plant surface (83%; n = 12), but the clear shortening of the proboscis of several of these individuals (70%; n = 10) suggested that the stylets were inserted. Lighter insects need to invest proportionally less of their resources in flight than heavier ones (Dixon & Kindlmann, 1999), and teneral fasting may confer aerodynamic advantages to alate aphids by reducing body weight at take-off. The labial tip of most teneral alates offered no resistance to the brush and easily moved across or away from the plant surface (80% moved with the first contact of the brush).…”