Cold tolerance of the maize orange leafhopper, Cicadulina bipunctata

Acute cold stress and supercooling capacity of Mediterranean fruit fly populations across the Northern Hemisphere (Middle East and Europe)

The Mediterranean fruit fly, Ceratitis capitata (Diptera: Tephritidae), holds an impressive record of successful invasion events promoted by globalization in fruit trade and human mobility. In addition, C. capitata is gradually expanding its geographic distribution to cooler temperate areas of the Northern Hemisphere. Cold tolerance of C. capitata seems to be a crucial feature that promotes population establishment and hence invasion success. To elucidate the interplay between the invasion process in the northern hemisphere and cold tolerance of geographically isolated populations of C. capitata, we determined (a) the response to acute cold stress survival of adults, and (b) the supercooling capacity (SCP) of immature stages and adults. To assess the phenotypic plasticity in these populations, the effect of acclimation to low temperatures on acute cold stress survival in adults was also examined. The results revealed that survival after acute cold stress was positively related to low temperature acclimation, except for females originating from Thessaloniki (northern Greece). Adults from the warmer environment of South Arava (Israel) were less tolerant after acute cold stress compared with those from Heraklion (Crete, Greece) and Thessaloniki. Plastic responses to cold acclimation were population specific, with the South Arava population being more plastic compared to the two Greek populations. For SCP, the results revealed that there is little to no correlation between SCP and climate variables of the areas where C. capitata populations originated. SCP was much lower than the lowest temperature individuals are likely to experience in their respective habitats. These results set the stage for asking questions regarding the evolutionary adaptive processes that facilitate range expansions of C. capitata into cooler temperate areas of Europe.

Quantitative Effects of Temperature and Exposure Duration on the Occurrence and Repair of Indirect Chilling Injury in the Fall Armyworm Spodoptera frugiperda

The fall armyworm (FAW) Spodoptera frugiperda is a long-distance migratory insect pest, and the invaded range of its recent expansion includes regions colder than the tropical and subtropical regions in East Asia. In order to understand the potential distribution of S. frugiperd in temperate and colder regions, we quantified the effects of temperature and exposure duration on the degree of indirect chilling injury caused to S. frugiperd under laboratory conditions. The adults were more tolerant to moderately low temperatures (3 to 15 °C) than the larvae and pupae. Survival decreased significantly when adult S. frugiperd were exposed to temperatures of 9 °C or lower. A time-temperature model suggested that indirect chilling injury began occurring at 15 °C. Survival was improved by short-term daily exposure to higher temperatures, indicating the existence of a repair mechanism for indirect chilling injury in S. frugiperd. The degree of repair depended on the temperature, but the relationship was not a simple direct proportion. These findings on indirect chilling injury and repair will improve the estimation of the potential distribution of S. frugiperd in temperate and colder regions.