SURVIVORSHIP, LIFE-HISTORY, AND CONCEALMENT - A COMPARISON OF LEAF MINERS AND GALL FORMERS

During the critical immature stages, folivorous insects exhibit different levels of concealment, which may affect their overall survival and success. I tested this proposition by comparing the survivorship of gall makers with that of leaf miners, which have similar life histories but do not produce galls. Final mortalities did not in fact differ between the two guilds, but the mortality of leaf miners was lower before the mid-larval stage, producing Type I and/or Type II survivorship. Gall formers approached Type III survivorship. Hypotheses are proposed for the divergence. Other life-history traits co-varied with survivorship pattern in the expected manner, except for generation time, which was longer for gall formers. The latter is attributed to constraints arising from the substrate requirements for gall formation and likely contributes to the similar final mortalities in the two guilds. Fast development in leaf miners and galling in the gall formers may be viewed as alternative, roughly equivalent but mutually exclusive strategies for reducing mortality. It is misleading to view one strategy as better than another; rather, each feeding type has its advantages and disadvantages, and the balance of these determines the relative success of that type for a given habitat.