| Estimates of the total number of arthropod species in existence are based, in part, upon assumptions about both the host specificity of tropical insects and their restriction to the forest canopy. It has been difficult to evaluate these estimates because of the paucity of available data. A recently discovered association between wood-boring longicorn beetles (Cerambycidae) and their host plants in the Brazil nut family (Lecythidaceae) inspired a year-long rearing project in the lowland Neotropical rain forest of central French Guiana. Branches severed from five species of Lecythidaceae, left in the canopy or placed on the ground, yielded 1,813 cerambycids belonging to 37 species. Few cerambycid species were restricted to the canopy, although there was a seasonal shift in stratum: they reproduced at both levels during the dry season, but almost exclusively at canopy level during the rainy season.; Each potential host was associated with a distinctly different complement of cerambycids. Couratari stellata and Gustavia hexapetala , characterized by foetid odors, consistently produced few cerambycids. I hypothesize that the foul odors are oviposition deterrents to Lecythidaceae specialists. Wood samples collected from the malodorous C. stellata , and from two well-colonized species, Lecythis poiteaui and Eschweilera coriacea, have been analyzed for both volatile and non-volatile compounds contributing to the foetid smells. Sulfur compounds were dominant components of C. stellata, while they were minor components or lacking in the two popular tree species.; Eschweilera coriacea and Lecythis poiteaui gave rise to large and diverse cerambycid guilds. Most species associated with E. coriacea demonstrated a high degree of host fidelity, while L. poiteaui gave rise to more species with relatively broad host ranges. Cerambycid distribution patterns are evaluated in relation to host toxicity, as revealed by antimicrobial bioassays. The results are in accord with the hypothesis that highly toxic plant species are prone to host specialized insect herbivores, but numerous factors appear to influence the predispostion towards host fidelity.; Overall, results suggest that tropical insects may show greater flexibility than some current hypotheses suggest. Many are indeed specialists, but most specialists can utilize a broader range of potential hosts under a variable range of conditions. |
