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Physiology, Biochemistry, Development, and Genetics
Introduction
The great grig, Cyphoderris monstrosa Uhler (Orthoptera: Prophalangopsidae), is a large (20-30 mm long, adults >1.5 g) ensiferan that inhabits montane coniferous forests of western North America (Morris and Gwynne 1978; Kumala et al. 2005). Cyphoderris monstrosa is nocturnal, emerging from below-ground burrows and climbing conifers to feed on staminate cones (Caudell 1904; Morris and Gwynne 1978; Ladau 2003). Males sing after dusk via tegminal stridulation (Morris and Gwynne 1978) from late May or early June until late August (Mason 1996). Cyphoderris Uhler species are active at much lower temperatures than is typical for acoustic insects, singing at temperatures near 0 °C (Morris and Gwynne 1978; Dodson et al. 1983; Morris et al. 1989). Cyphoderris monstrosa are thought to overwinter as late instars in burrows below the leaf litter layer (Gwynne 1995), but nothing is known about their low temperature biology.
Insects employ two dominant strategies to survive subzero temperatures: freeze avoidant insects depress the temperature at which their fluids freeze, but die upon ice formation, while freeze tolerant insects can withstand internal ice formation. Although orthopteran eggs are freeze avoidant (e.g., Hao and Kang 2004), many nymphs and adults are freeze tolerant (e.g., Alexander 1967). The mechanisms underlying freeze tolerance are unclear, but many freeze-tolerant insects accumulate low molecular weight cryoprotectants, including the disaccharide trehalose and free amino acid proline, both detected in hemolymph of freeze-tolerant New Zealand alpine weta, Hemideina maori Pictet and Saussure (Orthoptera: Anostosmatidae) (Neufeld and Leader 1998). Many freeze-tolerant insects accumulate glycerol (Lee 2010), but this cryoprotectant has not been detected in freeze-tolerant Orthoptera (Ramløv et al. 1992; McKinnon 2015). Regulating the location and temperature of ice nucleation is thought to be essential for insect freeze tolerance (Zachariassen and Kristiansen 2000). These ice nucleators may be endogenous (e.g., proteins) or exogenous (e.g., ice nucleating-active bacteria or ice crystals), and can be located in the hemolymph (e.g., H. maori; Sinclair et al. 1999) and tissues (e.g., the Malpighian tubules and fat bodies of Eurosta solidaginis; Mugnano et al. 1996).
Here, we characterise the cold tolerance strategy, the lower lethal limits, likely...