Cockroaches, like other invertebrates, have a diversity of responses to cold temperatures (Block, 1991). Each strategy entails energetic costs, with many interacting factors,
including the minimum temperature to which they are exposed, the variation in winter temperature, lifecycle stage, body size, habitat, availability of harborage, diet, snow cover, and particularly, water requirements and management (e.g., Sinclair, 2000). Several temperate cockroaches are active throughout winter, including the New Zealand species Parellipsidion pachycercum, Celato-blatta vulgaris, Cel. peninsularis, and Cel. quinquemacu-lata. The latter is a tiny (adult weight 0.1 g), brachypter-ous cockroach inhabiting alpine communities at altitudes greater than 1300 m asl, and is active even when the temperature of its microhabitat is below freezing (Zervos, 1987; Sinclair, 1997). Several North American species of Parcoblatta are similarly lively in winter (Horn and Han-ula, 2002). Blatchley (1920) wrote of Parc. pennsylvanica: "Cold has seemingly but little effect upon them, as they scramble away almost as hurriedly when their protective shelter of bark is removed on a day in mid-January with the mercury at zero, as they do in June when it registers 100 degrees in the shade." Tanaka (2002) demonstrated that in Periplaneta japonica the ability to move at low temperature is acquired seasonally. During winter, last instar nymphs recover from being buried in ice in < 100 sec, with some of them moving immediately; in summer, movement was delayed by > 600 sec.
As in other insects, two main physiological responses contribute to winter hardiness in cockroaches: freeze tolerance and the prevention of intracellular ice formation by supercooling. Regardless of the season, Cel. quinque-maculata is freeze tolerant, with a lower lethal temperature in winter. Supercooling points fluctuate throughout the year, but the insect uses potent ice nucleators to avoid extensive supercooling. Its level of protection is just adequate for the New Zealand mountains in which it lives, where the climate is unpredictable and temperatures as low as —4°C have been recorded in summer. This cockroach may undergo up to 23 freeze-thaw cycles during the coldest months and remain frozen for up to 21 hr. The added protection of buffered microhabitats is necessary for survival in some winters (Sinclair, 1997, 2001; Wor-land et al., 1997). The North American montane species Cryptocercus punctulatus lives in a more predictable seasonal climate, with the added climatic buffer of a rotting log habitat. It is freeze tolerant only in winter; it uses the sugar alcohol ribitol as an antifreeze in transitional weather, and as part of a quick-freeze system initiated by ice-nucleating proteins when the temperature drops (Hamilton et al., 1985). There was a 76% survival rate among individuals held up to 205 days at — 10°C, and winter-conditioned cockroaches that are frozen become active as soon as they are warmed to room temperature. Cold hardiness has also been studied in P. japonica (Tanaka and Tanaka, 1997), Parc. pennsylvanica (Duman, 1979), Perisphaeria spp., and Derocalymma spp. (Sinclair and Chown, 2005).
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