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Survival at low temperature of larvae of the pine processionary moth Thaumetopoea pityocampa from an area of range expansion

Hoch, Gernot, Toffolo, Edoardo Petrucco, Netherer, Sigrid, Battisti, Andrea, Schopf, Axel
Agricultural and forest entomology 2009 v.11 no.3 pp. 313-320
Notodontidae, Thaumetopoea pityocampa, ambient temperature, chilling injury, climatic factors, cold tolerance, freezing, global warming, insects, larvae, nests, night temperature, rearing, regression analysis, supercooling point, winter, Italy
1 Larvae of Thaumetopoea pityocampa (Lepidoptera: Notodontidae) develop throughout the winter, although their feeding activity and survival can be impaired by adverse climatic factors. The present study investigated the survival at low temperature of larvae originating from a population with range expansion in an alpine valley in Northern Italy. 2 The supercooling point of individually analysed larvae averaged at -7 °C. This value insufficiently described the cold hardiness of the larvae; 39% of the tested larvae were alive when returned to room temperature immediately after freezing. When larval colonies inside their nest were exposed to -17 °C for 1 h after gradual temperature decrease, survival was 70.4%. 3 Rearing of larvae in the laboratory at different day/night temperatures indicated an effect of cumulative chill injury on larvae. A logistic regression explained the relationship between negative thermal sum (h°C below 0 °C) received in the laboratory experiment and larval survival. A similar relationship was demonstrated between negative thermal sum and survival of larval colonies in the field. 4 In the laboratory experiment, some tested larvae were able to survive for up to 8 weeks without feeding depending on rearing temperature. As expected, feeding occurred only when larvae were reared at temperatures of 9 °C day/0 °C night. 5 We classify the larvae of T. pityocampa as being moderate freezing tolerant. The winter behaviour allows this species to track climate warming by a rapid expansion into those areas that become compatible with the insect's development.