Relative humidity preference and survival of starved Formosan subterranean termites (Isoptera: Rhinotermitidae) at various temperature and relative humidity conditions

Foraging groups of Formosan subterranean termites, Coptotermes formosanus Shiraki were tested for their relative humidity (RH) preference in a humidity gradient arena in the laboratory at a constant temperature of 26^oC. Five RH levels (9%, 33%, 53%, 75% and 98%) were maintained in the test arena comprising of a series of closed containers using dry silica gel, saturated salt solutions or distilled water alone. Termites gradually aggregated to the highest RH chamber in the arena. After 1 h, a significantly greater percentage of termites (~ 46%) aggregated to the highest RH chamber (98%) than to the lower RH chambers (≤ 75%). After 12 h, > 97% of the termites aggregated to the 98% RH chamber. In survival tests, where termites were exposed to 15 combinatorial treatments of 5 RH levels (9%, 33%, 53%, 75% and 98%) and 3 temperatures (20^oC, 28^oC and 36^oC) for a week, the survival was significantly influenced by RH, temperature and their interaction. A significantly higher mortality was observed on termites exposed to ≤75% RH chambers than to 98% RH chamber at the three temperatures and significantly lower survival was found at 36^oC than at 28^oC or 20^oC. The combination of temperature and RH plays an important role in the survival of C. formosanus.