Effect of Low Temperature Exposure on the Supercooling Point of Oriental Cockroach (Dictyoptera: Blattidae)

A system constructed with thermocouples and a conventional refrigerating bath was used to measure the freezing and melting points of various developmental stages of oriental cockroach, Blatta orientalis L., after exposure to different pre-freezing temperature conditions. Low temperature exposure of the oriental cockroach was not consistently effective in enhancing the supercooling capacity at various stages. There were minimal differences among the various developmental stages, and freezing points ranged −6.85 to −11.18°C. A significant lowering of freezing point (P< 0.05) was observed only from the first and second nymphal stages; freezing points were below −11°C after exposure at 5°C after 2 wks at 10°C. The melting points were consistently around 0°C (range of −0.19 to 0.31 °C). The relatively limited supercooling capacity of oriental cockroaches suggest that freezing avoidance by microhabitat selection is a major mechanism for overwintering of this insect.