The potato tuberworm, Phthorimaea operculella (Zeller) (Lepidoptera: Gelechiidae), is a worldwide pest of solanaceous crops especially devastating to potatoes. In the present study, we investigated the cold hardiness profile of acclimated and non-acclimated immature and adult stages of a field population of P. operculella. For both acclimated and non-acclimated individuals mean supercooling point (SCP) did not differ significantly among developmental stages. Unlike supercooling capacity, acclimation at 5°C for 5 days enhanced the ability to survive at subzero temperatures after a 2-h exposure. Median lethal temperature (LT 50 ) of all developmental stages (egg, late instar, pupa, and adult) decreased after acclimation, nevertheless only adults displayed a significant difference among acclimated and non-acclimated individuals concerning their LT 50 (À11.1 and À8.3°C, respectively). Generally, pupae were the most cold-tolerant developmental stage followed in decreasing order by the eggs and adults, whereas late instars were the least cold tolerant. Non-freezing injury above the SCP was well-documented for all developmental stages indicating a pre-freeze mortality and suggesting that P. operculella is considered to be chill tolerant rather than freeze intolerant. Nevertheless, given its high degree of cold hardiness relative to habitat temperatures, winter mortality of P. operculella due to low temperatures is not likely to occur and pest outbreaks may take place following a mild winter.

The potato tuberworm, Phthorimaea operculella (Zeller) (Lepidoptera: Gelechiidae), is a worldwide pest of solanaceous crops especially devastating to potatoes. In the present study we investigated the cold hardiness profile of short-term acclimated and non-acclimated immature and adult stages of a field population of P. operculella. Late instars displayed the lowest mean supercooling point, for both short-term acclimated and non-acclimated individuals, however, no significant differences were observed among developmental stages. Unlike supercooling capacity, acclimation at 5 oC for 5 days enhanced the ability to survive at subzero temperatures after a 2 h exposure. Mean lethal temperature (LTemp50) of all developmental stages (egg, late instar, pupa and adult) decreased after short-term acclimation, however only adults displayed a significant difference among acclimated and non-acclimated individuals concerning their LTemp50 (-11.1 and -8.3 oC, respectively). Generally, pupae were the most cold tolerant developmental stage followed in decreasing order by the eggs and adults, while interestingly late instars were the least ones. Non-freezing injury above the supercooling point was well documented for all developmental stages indicating a pre-freeze mortality and suggesting that P. operculella is considered to be chill tolerant rather than freeze intolerant. Nevertheless, given its high degree of cold hardiness, winter mortality of P. operculella due to low temperatures is not likely to occur and potential pest outbreak can take place following a mild winter.