Winter climates and coldhardiness in terrestrial insects

Abstract

Abstract. Overwintering insects must avoid injury and death from the freezing of tissues and from metabolic disruptions associated with exposure to low, non-freezing temperatures. The winter climates of the world are classified in relation to insect overwintering on the basis of their minimum temperatures and the duration of the winter (when temperatures are below the thermal range for activity and development). Outside the Tropical Wet zone, the severity of exposure to cold (temperature, snowfall, duration of exposure, predictability, variability) can vary from a few days at 0°C to months below -20°C with extremes as low as -60°C. The severity of the temperature exposure may be ameliorated by the selection by insects of overwintering sites (exposed, partly-exposed, protected). The relationships among overwintering habitats, the minimum winter temperature in climatic zones, and the supercooling points (SCP) of over 350 terrestrial insects from published reports were examined. Variability in the SCP among insects within each climatic zone and habitat was wide. Among the freeze-susceptible species that overwintered in exposed or partly-protected habitats the SCP and the cold severity of climate were correlated. This was not the case for insects that overwintered in protected habitats. The SCP's of freeze-tolerant insects were generally higher than the freeze-susceptible insects, and the SCP's were not tightly linked with the cold severity of climatic zone. Insects, both freeze-susceptible and freeze-tolerant, overwintering in exposed habitats had lower SCP's than insects from habitats that offered some protection from ambient temperatures. Thirty-eight species had reports of SCP's for different geographical locations. Although there were occasionally differences in the SCP's, there was no consistent pattern of insects having lower SCP's when overwintering in colder habitats. The incidence of freeze-tolerance was higher in boreal and polar climatic zones than in climatic zones with warmer winters. Holometabola insects had a higher incidence of freeze-tolerance than hemimetabola insects. Suggestions for future research directions are outlined.

More complex than expected: Cold hardiness and the concentration of cryoprotectants in overwintering larvae of five Erebia butterflies (Lepidoptera: Nymphalidae)

“…The apparently less common freeze tolerance occurs either in habitats with prolonged periods of extremely low temperatures (Turnock & Fields, 2005) or in unpredictable climates with repeated freeze-thaw events (Sinclair et al, 2003). We speculated earlier (Vrba et al, 2012) that lowland E. medusa is more likely to experience freezing temperatures without snow cover and freeze-thaw cycles than the alpine species.…”

“…In E. medusa, it is likely that the exposure to freezing temperatures initiated mechanisms that allow controlled freezing at relatively high subzero temperatures (Turnock & Fields, 2005). Although repeated freezing and thawing increases risks of tissue damage (cf.…”

Ecologically realistic modalities in arthropod supercooling point distributions

“…Likewise the cold hardiness of certain life stages of arthropods which otherwise show evidence of prefreeze mortality may also be measured with SCPs -e.g. eggs (Strathdee et al, 1995) or overwintering stages (Turnock & Fields, 2005) (who are more likely to "supercool"). Determination of the temperature thresholds used to discriminate modalities is, of course, habitat-specific, but the principle of applying conservative thresholds to separate animals "at risk" from animals that are sufficiently cold hardened (or contain less ice nucleating agents), is widely applicable.…”

“…Bale, 1991;Sinclair, 2001) and with the SCPs of some overwintering insects (e.g. Green, 1962;Sullivan, 1965;Tenow & Nilson, 1990;Turnock & Fields, 2005). The approach is also transferable to micro-modelling of mortality risk (cf.…”

“…Sinclair et al (2006) have used SCP data to model the likelihood of 5% of Continental Antarctic collembolans freezing at given microhabitat temperatures. The approach described in this analysis employs the same rationale -the belief that SCPs should be analysed in tandem with environmental temperatures (see also Turnock & Fields, 2005) -although here the aim is to arrive at a reliable, but conservative, assessment of the proportion of animals likely to be at risk from given microhabitat temperatures.…”