Temperature acclimation of the eastern subterranean termite Reticulitermes flavipes (Kollar) and implications for overwintering in a northern temperate climate

Populations of the eastern subterranean termite Reticulitermes flavipes (Kollar) are broadly distributed across North America and have shown regional differences associated with geographic location. Results from a limited number of temperature tolerance studies to date suggest that along their northern boundary, termites utilize a freeze-avoidant cold tolerance strategy, tunneling below the soil frost line during cold winter months. However, unlike many freeze-avoidant organisms, these insects are not thought to rely on the production or accumulation of cryoprotectants that would help to limit freezing risk. Instead, our data demonstrated a significant increase in supercooling point temperature associated with cold acclimation which would enhance risk of freezing. We also evaluated differences in the microbial community associated with the termite gut as changes in physiological and metabolic requirements of the termite host are likely to be reflected in the composition of the gut microbiome. Two microbial taxa that appear to shift in abundance in relation to changes in temperature include members of Elusimicrobia and Euryoarchaeota, both of which are involved in hydrogen-based metabolism in the termite gut by way of acetogenesis and methanogenesis, respectively. Fluctuations in the partial pressure of oxygen and hydrogen are thought to drive these associations which could be affected by temperature and overwintering strategy. For example, in subterranean insects that utilize a cold tolerance strategy involving tunneling deep in soil to avoid freezing, gas exchange would be severely limited resulting in a shift in the O₂/CO₂ concentration which would impose constraints on normal aerobic metabolism.