Temperature is among the key factors impacting the establishment and spread of invasive pests. The tomato leafminer Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) is one of the major pests attacking Solanaceae plants and is known to possess overwintering capacities. However, the cold hardiness of T. absoluta pupae is poorly documented. In this study, we investigated the effect of constant temperature and stepwise cooling on T. absoluta pupae under laboratory conditions. For this purpose, bioassays on pupal development under constant temperature (5°C) for 30, 60 and 90 days, and stepwise changes in temperature (11, 10 and 8°C; in this order every 30 days), were assessed. We found that exposure to 5°C for 30 and 60 days did not affect the post-cooling emergence time of adults compared to the control. Pupae completed their development after 60 days of cold exposure at 5°C, but more adults emerged after 30 than 60 days. Even though alive pupae were observed after 90 days of cold exposure at 5°C, no adults emerged. External colours of pupae depended on the duration of cold periods, and green pupae obtained after 30 and 60 days were found to be positively correlated with the emergence of adults. When pupae were kept at 11°C for 30 days, 47% emerged, and when the temperature was changed to 10, only 12% of pupae emerged for the period 31–60 days. However, the decrease of the temperature to 8°C yielded no emergence for the period 61–90 days. Our study provides useful information to better understand the population dynamics of overwintering T. absoluta, and to underpin the development of monitoring and control strategies for the pest.

Broad-spectrum insecticides are the main control measure of the invasive and economically damaging soybean aphid (Aphis glycines) in North America, although biological control by resident natural enemies can also greatly diminish population levels. One such natural enemy is the accidentally introduced Eurasian parasitoid Aphelinus certus (Hymenoptera: Aphelinidae), though its impact appears to be limited by low rates of parasitism early in the growing season. We tested the hypothesis that A. certus might experience high overwintering mortality. In the laboratory, we used thermocouple thermometry to measure the supercooling points of diapausing parasitoids and assessed parasitoid survival after exposure to ecologically relevant durations of low temperature. We found A. certus to be freeze-intolerant with a median supercooling point of −28°C. When exposed to temperatures of 0°C for up to 7 months, adults emerged only after exposures of at least 60 days and survival decreased with durations beyond 150 days. We also conducted in-field studies at sites from northern Minnesota to southern Iowa to determine if diapausing A. certus could overwinter above and below the snowpack. Survival was negatively correlated with increasing latitude and was greater for parasitoids placed on the ground than 1 meter off the ground, likely due to the warmer and stabler temperatures of the subnivean microclimate. Our results suggest that A. certus is capable of overwintering in the region inhabited by soybean aphid but may experience substantial mortality even under ideal conditions. Climate change is predicted to bring warmer, drier winters to the North American Midwest, with decreased depth and duration of snow cover, which may further reduce overwintering survival.

The spotted wing drosophila, Drosophila suzukii, is an invasive pest in Europe and North America. Access to resources may be challenging in late fall, winter and early spring and flies may suffer from food deprivation along with cold stress in these periods. Whereas a plethora of studies have been performed on the overwintering capacity of D. suzukii, the effects of starvation on the fly's cold tolerance have not been addressed. In the present study, young D. suzukii adults (reared at 25°C, LD 12:12 h) were deprived of food for various periods (0, 12, 24 and 36 h), after which chill coma recovery time, critical thermal minimum, as well as acute and chronic cold tolerance were assessed. Additionally, the body composition of adults (body mass, water content, total lipid, glycerol, triglycerides, glucose and proteins) before and after starvation periods was analysed to confirm that starvation had detectable effects. Starved adults had a lower body mass, and both lipid and carbohydrate levels decreased with starvation time. Starvation slightly increased critical thermal minimum and affected chill coma recovery time; however, these changes were not gradual with starvation duration. Starvation promoted acute cold tolerance in both sexes. This effect appeared faster in males than in females. Food deprivation also led to enhanced survival to chronic cold stress. Short-term starvation was thus associated with significant changes in body composition in D. suzukii, and these alterations could alter some ecologically relevant traits related to cold tolerance, particularly in females. Our results suggest that food deprivation during short time (<36 h) can promote cold tolerance (especially survival after a cold stress) of D. suzukii flies. Future studies should address the ecological significance of these findings as short food deprivation may occur in the fields on many occasions and seasons.

Pistachio twig borer, Kermania pistaciella is an important pest of pistachio trees. It has an univoltine life-cycle and its larvae tunnel and feed inside pistachio twigs for almost 10 months each year. The last larval instars overwinter inside the twigs. Survival/mortality associated with low temperatures during overwintering stage is currently unknown. We found that overwintering larvae of the Rafsanjan (Iran) population of K. pistaciella rely on maintaining a stably high supercooling capacity throughout the cold season. Their supercooling points (SCPs) ranged between −19.4 and −22.7°C from October to February. Larvae were able to survive 24 h exposures to −15°C anytime during the cold season. During December and January, larvae were undergoing quiescence type of dormancy caused probably by low ambient temperatures and/or changes in host tree physiology (tree dormancy). Larvae attain highest cold tolerance (high survival at −20°C) during dormancy, which offers them sufficient protection against geographically and ecologically relevant cold spells. High cold tolerance during dormancy was not associated with accumulation of any low-molecular mass cryoprotective substances. The SCP sets the limit of cold tolerance in pistachio twig borer, meaning that high mortality of overwintering populations can be expected only in the regions or years where or when the temperatures fall below the average larval SCP (i.e., below −20°C). Partial mortality can be expected also when temperatures repeatedly drop close to the SCP on a diurnal basis.

The carob moth, Ectomyelois ceratoniae, a pest of Punica granatum, overwinters as a larva. In this study, physiological changes, water content, cold hardiness and supercooling points (SCPs) in relation to ambient temperature in the overwintering period (October to March) and changes of these factors between diapausing (February) and non-diapausing (September) larvae were studied. Pupae that were derived from diapausing larvae (April) and  from non-diapausing larvae (August) were also compared. Total body sugar, lipid and protein contents increased with decrease in the temperature and reached the highest levels (12.82, 1.99 and 6.11 mg g−1 body weight, respectively) in February, but glycogen content decreased and reached the lowest level (1.12 mg g−1 body weight) in February. There were significant differences in the levels of these compounds between diapausing and non-diapausing larvae, and pupae that were derived from diapausing and non-diapausing larvae. Trehalose and myo-inositol contents increased during diapause and reached the highest levels (0.50 and 0.07 mg g−1 body weight, respectively) in February. There were significant differences in the levels of these compounds between diapausing and non-diapausing larvae, but the differences between pupae that were derived from diapausing and non-diapausing larvae were not significant. The SCP of diapausing larvae (−17.3 °C) was significantly lower than in the non-diapausing larvae (−12.0 °C). SCP decreased gradually in autumn and reached the lowest level in the middle of winter. Changes of cold hardiness were inversely proportional to SCP changes. The lowest levels of water (65%) and weight (43.13 mg) were recorded in January and March, respectively. Most probably, lipids play a role as energy reserve, and low-molecular weight carbohydrates and polyols provide cryoprotection for overwintering larvae of the carob moth. Since the overwintering larvae die at temperatures above the SCP, the carob moth larvae were found to be a chill-intolerant insect.

Frost damage was evaluated in 1-year-old olive trees in the cultivars ‘Arbequina’, ‘Cornicabra’, ‘Empeltre’, ‘Frantoio’, ‘Hojiblanca’, ‘Manzanilla Cacereña’, ‘Nevadillo de Jaén’, ‘Picual’, ‘Picudo’ and ‘Verdial de Badajoz’ in Madrid, Spain. Temperatures fell to −6.5 and −10.5°C on 11 November and 16 December 2001, respectively. In May frost damage was visually assessed. The olive trees were pruned to the ground and dry matter was quantified in shoots and leaves with and without signs of frost damage. In August resprouting was visually evaluated. Visual assessment overestimated frost damage compared to the quantitative evaluation. Leaves had a lower resistance to frost than shoots. Shoot frost resistance was linearly correlated to the cultivar's resprouting capacity. Significant differences in frost resistance were found between cultivars. ‘Cornicabra’ and ‘Arbequina’ had a low percentage of frost-damaged shoots and a high resprouting capacity after frost. The cultivars which were the least resistant to frost were ‘Empeltre’, ‘Frantoio’ and ‘Hojiblanca’. These cultivars had a high percentage of frost-damaged shoots and almost no resprouting capacity. ‘Picual’, ‘Picudo’, ‘Verdial de Badajoz’, ‘Manzanilla Cacereña’ and ‘Nevadillo de Jaén’ had an intermediate frost resistance.