Comparative analysis of flight muscle function in microinsects Megaphragma viggianii (Hymenoptera: Trichogrammatidae) and Paratuposa placentis (Coleoptera: Ptiliidae)

The wing structure, kinematics, and aerodynamics of miniature insects differ drastically from those of medium- and large-sized species. However, the structural and functional features of their wing musculature that contribute to these differences remain largely unknown. We analyze flight muscle function in two species of microinsects from different orders. Both employ indirect muscles to power flight, but the ratio of sizes between the two main muscle groups differs fundamentally, and M. viggianii is characterized by a unique hypertrophy of the dorsal longitudinal muscles. In both, aerodynamic power estimates from computational fluid dynamics simulations match known ranges for small insects when normalized by body or muscle mass. However, power outputs calculated separately for downstroke and upstroke phases reveal major mismatches, especially in M. viggianii where upstroke demands exceed typical muscle capabilities. We argue that elastic energy storage in the thorax shifts work between muscle groups, with much of the energy from the dominant muscles stored during one phase and released in the other. Thus, we have shown that, despite the convergent similarity in wing structure among miniature insects known as ptiloptery, the mechanics of the wing apparatus can differ fundamentally across different groups of microinsects.