Semester of Graduation
Master of Science (MS)
Substrate moisture is a critical environmental factor for the survival and behavior of subterranean termites (Blattodea: Rhinotermitidae). The invasive Formosan subterranean termite (Coptotermes formosanus) and the native eastern subterranean termite (Reticulitermes flavipes) co-occur in the southeastern United States, but C. formosanus is predominant in subtropical and R. flavipes is more common in temperate regions. The difference in their geographic distributions is largely attributed to their different behavioral and physiological ecology. While ample research has been done on foraging behavior of the two species, there was no empirical evidence for the effects of constant soil moisture on their foraging activity and colony survival. In addition, subterranean termites rely on soil moisture to maintain water balance, and an important physiological mechanism of desiccation resistance in insects is the prevention of transpirational water loss via cuticular hydrocarbons (CHCs). CHCs exhibit plastic response to environmental variations in many insects. Previous research on termite CHCs has analyzed their seasonal and geographical variations as well as the role in chemical communication, however, studies examining CHC plasticity and its correlation with desiccation resistance are lacking. In this study, we investigated the effects of soil moisture on the behavior and physiology of subterranean termites. We hypothesized that foraging activity and survivorship of both C. formosanus and R. flavipes alter in response to different substrate moisture regimes, and the effects differ between the two species. To test this, the tunnel area, survivorship, and food consumption were documented for 28 days under six sand moisture conditions (0%, 1%, 5%, 15%, 25%, 30%) in both C. formosanus and R. flavipes. We found that, in both species, no tunneling or feeding activity was performed at 0% substrate moisture, while no significant difference was found on tunnel area, food consumption, or survivorship among 5%, 15%, 25%, or 30%. Survivorships of termites at 0% and 1% substrate moisture were significantly lower than that at 5%, 15%, and 25% for C. formosanus. For R. flavipes, survivorships at 0% and 1% substrate moisture were significantly lower than that at 5%, 15%, and 30%. In both species, a minimum of 1% substrate moisture is needed for foraging and 5% is required for colony survival. To examine the physiological effects, we further hypothesized that desiccation resistance and CHC profiles of C. formosanus change in response to soil moisture conditions. Upon acclimation to soil moisture conditions of 5%, 15%, and 25%, we found that C. formosanus workers expressed notable changes in CHC profiles in both linear and methyl-branched alkanes, where 12 of the 20 cuticular hydrocarbons detected expressed a significant increase in quantity at 5% soil moisture when compared to 25% soil moisture. Lastly, desiccation resistance of workers was significantly higher upon acclimation to 5% sand moisture (20.36 ± 0.79 hours, survival time under desiccation stress) when compared to 15% (17.47 ± 0.63 hours) and 25% (15.38 ± 0.65 hours). Our results demonstrate the effects of substrate moisture on the behavior and physiology of subterranean termites and suggest that CHC plasticity may be important for the climate adaptation of subterranean termites.
Richardson, Steven J., "SOIL MOISTURE MEDIATED BEHAVIORAL AND PHYSIOLOGICAL ALTERATIONS OF COPTOTERMES FORMOSANUS AND RETICULITERMES FLAVIPES (BLATTODEA: RHINOTERMITIDAE)" (2022). LSU Master's Theses. 5645.