Effects of cold acclimation, cooling rate and heat stress on cold tolerance of the potato tuber moth Phthorimaea operculella (Lepidoptera: Gelechiidae)

Abstract

This study was carried out to investigate the effects of cold acclimation, cooling rate and heat stress on supercooling capacity and cold hardiness of the potato tuber moth (PTM), Phthorimaea operculella Zeller (Lepidoptera: Gelechiidae). Supercooling points (SCP) of first and last instar larvae, prepupae and pupae were -21.8, -16.9, -18.9 and -18.0°C, respectively. Cold acclimation (1-week at 0 and 5°C) did not affect SCPs of acclimated last instar larvae, prepupae and pupae. LT50s (lower lethal temperature for 50% mortality) for first and last instar larvae, prepupae and pupae were -15.5, -12.4, -17.9 and -16.0°C, respectively. Cold acclimation resulted in a significant decrease in mortality of all developmental stages. In addition, the mortality rates of the different developmental stages decreased with decrease in cooling rate. In addition, heat hardening (kept at 40°C for 2 h) significantly reduced mortality of all developmental stages exposed to LT50 conditions, suggesting that heat hardening also affects cold tolerance. Results indicate that none of the stages could tolerate subzero temperatures below their SCPs, indicating that this species might be a chill tolerant insect. These adaptive responses may allow PTM to enhance its cold tolerance and colonize cold regions.