Virtually all studies of plant insect interactions presume that the interaction is between the plant and the insect, but in the case of cerambycid beetles the interaction may actually be mediated by a symbiont. Wood-boring cerambycid beetles harbor intracellular gut yeasts hypothesized to provide their hosts with nutrients, which may also be the insect's first line of defense against secondary plant metabolites. Neotropical members of the Brazil nut family (Lecythidaceae) host a well-defined guild of specialist cerambycid beetles, some of which feed on trees with marked bioactive properties. Because beetle gut yeasts can be maintained in culture outside of the host, they are amenable to direct tests of either favorable or inhibitory impacts of plant extracts. Beetle rearing data and prior bioassays of host plant extracts have shown that wood from Couratari stellata, a poorly colonized tree species, inhibits the growth of the human pathogen Candida albicans. If yeasts enable wood-boring beetles to feed on 'indigestible' plant tissues (or protect them from plant toxins), trees rich in antifungal metabolites should be shielded from beetle attack. The hypotheses to be tested in this project are:
1. Wood extracts from the poorly colonized tree Couratari stellata will inhibit the growth of yeasts isolated from cerambycids associated with favored tree species. 2. The few cerambycids that reproduce in Couratari stellata will not host gut yeasts, or will be associated with microbes that are able to grow in the presence of C. stellata wood extracts.
This will be the first study of interactions among yeast symbionts, a group of closely related tropical beetles, and host plant chemistry. Symbionts associated with wood-boring beetles may play an important, but largely unrecognised role in forest ecology. The City College of New York is a minority institution, and this project was designed to be conceptually and methodologically accessible to urban undergraduate students with little previous exposure to the environmental sciences. Minority undergraduate and graduate students will participate in an international field expedition, develop a broad range of laboratory skills, and present their research results at a national meeting.
