D3102: Desiccation tolerance and influence of relative humidity on the survival of different castes in the Formosan subterranean termite, Coptotermes formosanus Shiraki

Desiccation is an important environmental stressor that affects the survival of insects. The Formosan subterranean termites, Coptotermes formosanus, encounter varying levels of humidity during foraging activity of the non-reproductive individuals (workers and soldiers) and swarming of the reproductives (alates). In this study, we evaluated effects of different levels of relative humidity (RH), 15%, 33%, 55%, 75%, 85% and 98%, on survival of workers and soldiers, and female and male alates of C. formosanus. The assay was conducted without substrate moisture, and the lethal time 100% (LT100) were documented for each RH level. We found that, at 98% RH, LT100 were 13 and 6 days for non-reproductives and alates, respectively, while LT100 was less than one day for all castes at 15% RH. In addition, we evaluated desiccation resistance by quantifying water loss of workers, soldiers and alates when exposed to desiccants (silica gel). Water loss was reported to be highest for workers, followed by male and female alates, and soldiers. The results indicate that dietary water or substrate moisture might be needed for higher survival rate. Although workers was the least resistant caste to desiccation, the greater LT100 at higher RH levels might be attributed to behavioral regulation and physiological mechanisms to be further investigated.