Laboratory evaluation of subterranean termite (Isoptera: Rhinotermitidae) response to "thermal shadows" in an environment of homogenous temperature

Subterranean termites, Reticulitermes spp., from the state of Virginia were bioassayed in the laboratory to determine their preferred temperature range within a sand substrate. The mean preferred temperature for termite workers was 22.5 degrees C, with a range of 18-27 degrees C. Termites were also assayed to determine their behavioral response to spot locations of different temperature within an arena of homogeneous (ambient) temperature. These spot locations, or thermal shadows, were artificially created by placing a small heated or cooled reservoir on top of a bioassay arena in a specific location. This way the heating or cooling effects created a spot of different temperature within the arena which was held at ambient temperature. The ambient temperatures selected for testing were 20 degrees C and 25 degrees C. Both of these temperatures fell within the termites preferred temperature range. Both warm and cool thermal shadows were tested and shadow temperatures were selected from within and outside the termites preferred temperature range. Significantly more subterranean termites aggregated in the cool thermal shadows than in the ambient portions of the arena. When the ambient temperature of the arena was held at 25 degrees C significantly more termites aggregated in the cool thermal shadow (20 degrees C) than in the other portions of the arena (25 degrees C). When the ambient temperature was held at 20 degrees C significantly more termites aggregated within a cool thermal shadow at 15 degrees C even though this temperature was outside the preferred temperature range. Subterranean termites did not respond to warm thermal shadows therefore the number of termites aggregating within the warm thermal shadow was not significantly different from those in the ambient portions of the arena.