Comparing wing loading, flight muscle and lipid content in ant-attended and non-attended Tuberculatus aphid species

Although all Tuberculatus aphids possess wings, some species associated with ants exhibit extremely low levels of dispersal compared with those not associated with ants. Furthermore, phylogenetic interspecific comparisons find significantly higher wing loading (i.e. higher ratio of body volume to wing area) in ant-attended species. This observation indicates that ant-attended species may allocate more of their body resources to reproductive traits (i.e. embryos) rather than flight apparatus (i.e. wings, flight muscle and lipid). The present study focuses on two sympatric aphid species and aims to investigate the hypothesized trade-off in resource investment between fecundity and the flight apparatus; specifically, the ant-attended Tuberculatus quercicola (Matsumura) and non-attended Tuberculatus paiki Hille Ris Lambers. Species differences are compared in: (i) morphology, (ii) embryo production, (iii) triacylglycerol levels and (iv) wing loading and flight muscle. The results show that T. quercicola has a larger body volume, higher fecundity and higher wing loading compared with T. paiki, which has a smaller, slender-shaped body, lower fecundity and lower wing loading. No significant difference is found between the species with respect to the percentage of triacylglycerol content in dry body weight. The flight muscle development is significantly lower in T. quercicola than in T. paiki. These results indicate that the additive effect of higher wing loading and the lower amount of flight muscle development in T. quercicola may increase the physical difficulty of flight, and hence be responsible for its lower dispersal ability. The trade-off between fecundity and dispersal documented in wing-dimorphic insects may therefore be applicable to T. quercicola, which has fully developed wings.