Effect of larval growth conditions on adult body mass and long-distance flight endurance in a wood-boring beetle: Do smaller beetles fly better?

The tropical fig borer, Batocera rufomaculata De Geer, is a large beetle that is a pest on a number of fruit trees, including fig and mango. Adults feed on the leaves and twigs and females lay their eggs under the bark of the tree. The larvae bore into the tree trunk, causing substantial damage that may lead to the collapse and death of the host tree. We studied how larval development under inferior feeding conditions (experienced during development in dying trees) affects flight endurance in the adult insect. We grew larvae either in their natural host or on sawdust enriched with stale fig tree twigs. Flight endurance of the adults was measured using a custom-built flight-mill. Beetles emerging from the natural host were significantly larger but flew shorter distances than beetles reared on less favourable substrates. There was no difference in the allometric slope of wing area with body mass between the beetles groups; however flight muscle mass scaled with total body mass with an exponent significantly lower than 1.0. Hence, smaller beetles had proportionally larger flight muscles. These findings suggest that beetles that developed smaller as a result from poor nutritional conditions in deteriorating hosts, are better equipped to fly longer distances in search of a new host tree.