| Two basic, largely untested premises of theory on host plant selection by insect herbivores are (1) that choice of host plant affects fitness in nature, and (2) that the relative effects of different hosts on fitness are predictable through time. I tested these hypotheses in a population of the moth Rothschildia lebeau (Lepidoptera: Saturniinae: Saturniinae) feeding on its three primary host plant species in a Costa Rican dry forest (Sector Santa Rosa, Area de Conservacion Guanacaste). In multiple R. lebeau generations, experimental cohorts of caterpillars were followed on naturally occurring trees to measure a suite of fitness-related performance variables as a function of host plant species.; Chapter 1 demonstrates that the host Spondias mombin was consistently associated with relatively low caterpillar survival, long development times, but large final adult size. The converse was true of the host Exostema mexicanum. Depending on the generation, performance on the host Casearia nitida was more like S. mombin or E. mexicanum. Chapter 2 provides evidence that adult body size is positively related to male mating success. Overall, host plant use in this system appears to involve a tradeoff between low survival and large adult size, mediated by development time.; Chapters 3 and 4 examine variation in host-related performance at the level of R. lebeau families. Chapter 3 demonstrates that variation in performance among families resulted from some families simply performing better than others, regardless of host plant species. Chapter 4 shows that initial offspring size (neonate caterpillar mass) was positively related to growth and survival, which suggests that performance differences among families were, in part, the result of differences in initial offspring size.; For R. lebeau in Santa Rosa, I found that host plant species indeed had significant effects on most measured components of fitness. In the aggregate, larval survival, development time, and final adult size covaried at the level of host. Thus, which was the "better" host from the perspective of an ovipositing female was not obvious: it will depend partly on whether making a few large offspring (S. mombin) is better than making many small offspring (E. mexicanum). |
