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

Abstract

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. LT 50 s (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 LT 50 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.

Cold hardiness attributes of a field population of the potato tuberworm, Phthorimaea operculella

“…According to the most recent classification of insects related to cold tolerance (Bale, 2002), P. operculella can be classified in the category of insects that are chill tolerant rather than freeze intolerant. In agreement with our observations, Hemmati et al (2014) also reported the incapability of a laboratory colony of P. operculella to tolerate subzero temperatures above their SCPs, though to a lesser extent. In agreement with our observations, Hemmati et al (2014) also reported the incapability of a laboratory colony of P. operculella to tolerate subzero temperatures above their SCPs, though to a lesser extent.…”

“…In most species supercooling capacity is regarded to be stage specific (Sømme, 1982;Lee, 1991). This is in agreement with previous reported studies where acclimation at 5 and 0°C for 1 week did not alter the supercooling capacity of P. operculella (Hemmati et al, 2014). Moreover, given that individuals originated from field-collected potatoes that were harvested in mid-September, when already minimum air temperatures in this area dropped below 10°C, both immature stages and adults may already have undergone cold acclimation in the field.…”

Cold tolerance characteristics of Korean population of potato tuber moth, Phthorimaea operculella (Zeller), (Lepidoptera: Gelechiidae)

“…Followed by eggs the next development stage having a low SCP were first and second instars while later instar larvae, late pupae and adult had higher supercooling points. Among the larval stages of PTM, Hemmati et al (2014) found the lowest SCP value for the first instar, whereas it was highest in case of last instar larvae for an Iranian population, which is in line with our study. Park et al (2017) also found the lowest SCPs for the egg stage of Parnassius bremeri.…”

“…The lowest supercooling point of eggs and early larvae may be due to their small sizes (Carillo & Cannon 2005;Hahn et al 2008;Zheng et al 2011;Hemmati et al 2014). Followed by eggs the next development stage having a low SCP were first and second instars while later instar larvae, late pupae and adult had higher supercooling points.…”

“…The egg was reported to be the most and the adult the least cold tolerant stage of the invasive population of PTM in Korea (Choe & Park 1980). Cold tolerance study of the PTM has been carried out with different laboratory and field populations in a variety of geographical regions (Hemmati et al 2014;Andreadis et al 2016) involving all developmental stages to provide some information on the supercooling capacity and lower lethal temperature. Further cold tolerance studies can give some insight into potential adaptations of the insect and their distribution and range expansion under harsh weather condition of temperate regions.…”