Sigma Xi Grant—example of Proposal

Plant galls are insect-induced tumor-like growths of plant tissue which nourish and protect developing insect larvae. In all published studies to date, gall size varies (1). Numerous studies demonstrate a positive relationship between success (probability of emergence of the gall-former) and gall size (2-4). Typically, increasing gall size is interpreted as an adaptation to facilitate parasitoid avoidance (5). This view assumes parasitism occurs after galls attain full size. If however, parasitoids attack gall-former larvae during the gall growth phase and limit further gall growth, then the relationship between gall-former success and gall size becomes complicated, and the explanation of optimal gall size as solely an adaptation to thwart parasitism is confounded. The research proposed herein will examine parasitism’s effect in limiting gall growth (driving gall size distribution) and the success of Belonocnema treatae, a host-specific gall-forming cynipid wasp (6). To determine the relationship between success and gall size in the presence or absence of parasitism a series of bagging experiments will be performed on ten of the gall-former’s host trees, Quercus fusiformis, plateau live oak, at SWT’s Freeman Ranch. Prior to emergence of the gall inducer in the spring of 1999, 20 nytex mesh bags will be placed over branches within each tree. Upon emergence females will be placed inside bags and allowed to oviposit. To create parasitized (unbagged) and unparasitized (bagged) treatments, 10 bags from each tree will then be removed. During Fall 1999 galls from each treatment will be collected, placed individually in gelatin capsules, incubated in the laboratory, scored daily for emergent B. treatae , and measured to the nearest 0.01mm with dial calipers. Two hypotheses will be tested. The hypothesis that the probability of successful emergence of B. treatae increases with increasing gall size will be tested within each treatment. The slope of the relationship will differ between treatments if parasitoids influence (limit) gall size. Mean gall size and percent success (emergents per gall) will also be compared between treatment groups (ANOVA). If mean gall size and success do not differ between treatments, then parasitism does not limit further gall growth. This result would suggest that gall size is an adaptation for parasitoid avoidance. If gall size distribution differs between treatments then parasitoids directly influence gall size distribution. This result would cast doubt on the parasitoid avoidance hypothesis and lead to further study to uncover the adaptive significance of large gall size.