Supercooling Differences in the Eastern Subterranean Termite (Isoptera: Rhinotermitidae)

Abstract

Supercooling points were determined for untreated field-collected and untreated laboratory-maintained Reticulitermes flavipes (Kollar) workers and soldiers. Workers treated with antibiotics or had their hindgut-protozoa removed by exposing them to oxygen under pressure to determine the effects of absence of the hindgut fauna on supercooling. Supercooling points were compared between live and freshly-killed workers to determine whether supercooling in this species might be simply due to the biochemical properties of body fluids. Laboratory-maintained workers were also subjected to desiccation, starvation, or atmospheric pressure to determine their effects on supercooling. Supercooling points were lowest for laboratory workers treated with antibiotics and those that fed on brown paper-toweling for 7 d. Untreated field-collected workers had significantly higher supercooling points than untreated laboratory-maintained workers (−6.06 ± 0.79°C vs −9.29 ± 2.38°C, P < 0.0001). Both untreated field-collected and laboratory soldiers had significantly lower supercooling points than their respective workers (−7.39 ± 2.01°C vs −6.06 ± 0.79°C, P < 0.0001; and −11.60 ± 2.53°C vs −9.29 ± 2.38°C, P< 0.0001, respectively). There was no significant association between termite body mass and supercooling points for both laboratory and field termites (P= 0.0523 and P = 0.6242) or water content of laboratory termites and supercooling points (P = 0.1425). Defaunated workers had significantly lower supercooling points (−10.34 ± 2.38°C) than normally faunated workers (−9.48 ± 1.85°C)(P= 0.0095) suggesting that the symbiotic fauna may have higher supercooling points and act as ice nucleators in the termite hindgut. Starved and desiccated workers had significantly lower supercooling points (−10.38 ± 2.70°C and −10.39 ± 2.38°C, respectively) than their corresponding control groups (−9.87 ± 2.11°C and −9.89 ± 1.94°C; P = 0.0454; P = 0.0234, respectively) and untreated workers (−9.29 ± 2.38°C; P= 0.0021; P= 0.0011) suggesting that some forms of physical stress might lower the supercooling point.