Obligate annual and successive facultative diapause establish a bet-hedging strategy of Rhagoletis cerasi (Diptera: Tephritidae) in seasonally unpredictable environments

To cope with temporal and spatial heterogeneity of habitats, herbivorous insects in the temperate zone usually enter diapause that facilitates synchronization of their life cycle with specific stages of host plants, such as fruit ripening. In the present study, we address those factors regulating dormancy responses as part of a ‘longer strategy’ to persist and thrive in temperate environments, focusing on Rhagoletis cerasi, a univoltine, oligophagous species, which overwinters as pupae and emerges when host fruits are available for oviposition at local scale. To ensure population survival and reproduction at habitats with ecological heterogeneity, R. cerasi has evolved a sophisticated diapause strategy based on a combination of local adaptation and diversified bet-hedging strategies. Diapause duration is determined both by (i) the adaptive response to local host fruit phenology patterns (annual diapause) and (ii) the plastic responses to unpredictable inter-annual (temporal) climatic variability that drives a proportion of the populations to extend dormancy by entering a second, successive, facultative cycle of prolonged diapause as part of a bet-hedging strategy. Besides the dormant periods, post-diapause development (which varies among populations) exerts ‘fine tune’ adjustments that assure synchronization and may correct possible errors. Adults emerging from pupae with prolonged diapause are larger in body size compared with counterparts emerging during the first year of diapause. However, female fecundity rates are reduced, followed by an extended post-oviposition period, whereas adult longevity remains unaffected. Overall, it appears that R. cerasi populations are adapted to ecological conditions of local habitats and respond plastically to unpredictable environmental (climatic) conditions. © 2017 The Royal Entomological Societ

Local adaptation, intrapopulation adult emergence patterns, sex and prolonged diapause regulate the rate of postwinter development in pupae of the European cherry fruit fly

We used the European cherry fruit fly, Rhagoletis cerasi (Diptera: Tephritidae), an oligophagous, univoltine species that overwinters as pupae, to determine the geographical variation in postwinter development of pupae with annual and prolonged diapause in geographically isolated populations with various levels of gene flow rates. We tested the hypothesis that emergence patterns within a population (early- vs. late-emerged adults) and local adaptation of populations from different habitats would affect the rate of postwinter development of pupae that yield adults during the first year of diapause. We also hypothesized that postwinter development of pupae with prolonged dormancy would differ among geographical isolated populations with gene flow. Our results revealed that (a) postwinter developmental period of pupae differ among genetic distant populations in the absence of intrapopulation variability in emergence patterns, and (b) temperature exerts a differential effect on postwinter developmental time in populations from both different and similar habitats. Prolonged dormancy seems to minimize population effects on postwinter developmental time. Females finished their postwinter development earlier than males. Population is a significant predictor of postwinter development for R. cerasi pupae with annual diapause but not for those that with a prolonged dormancy schedule. © 2017 The Linnean Society of London

Chill coma recovery of Ceratitis capitata adults across the Northern Hemisphere

The Mediterranean fruit fly, Ceratitis capitata (Diptera: Tephritidae), is an invasive pest, that is currently expanding its geographic distribution from the Mediterranean coasts to more temperate areas of Europe. Given that low temperature is a primary determinant of insect species’ range boundaries especially in the Northern Hemisphere with pronounced seasonality, we used chill coma recovery time for assessing latitudinal clines in basal chill tolerance of C. capitata adults. We selected six populations obtained from areas with broad climatic variability based on the main bioclimatic variables of temperature and precipitation, spanning a latitudinal range of about 19° from Middle East to Central Europe. Adults were exposed to 0 °C for 4 h, and time to regain the typical standing position of a fly at 25 °C were recorded. The post-stress survival after a period of 8 days was also recorded. Results revealed that adults from Israel and Austria were less chill tolerant than those from Greece, resulting in curvilinear trends with latitude. Analysis of macroclimatic conditions revealed combined effects of latitude (as a proxy of photoperiod) and macroclimatic conditions on chill coma recovery time. Nonetheless, there was not a deleterious effect on post-recovery survival, except for flies obtained from the northern most point (Vienna, Austria). Overall, it seems that evolutionary patterns of basal chill coma recovery time of C. capitata adults are driven mainly by local climatic variability. © 2022, The Author(s)

Effects of photoperiod and relative humidity on diapause termination and post-winter development of Rhagoletis cerasi pupae

The European cherry fruit fly, Rhagoletis cerasi (Diptera: Tephritidae), is a univoltine species that undergoes obligatory summer-winter diapause at pupal stage in the soil (2-5 cm) beneath host trees. To study the effects of photoperiod and relative humidity on diapause termination and post-winter developmental duration of R. cerasi, pupae collected from Dossenheim (Germany) were exposed to different photoperiod or relative humidity regimes during a chilling period ranging from 2 to 8.5 months. Specifically, pupae were exposed to four photoperiod regimes: (a) light conditions (24L:00D), (b) dark conditions (00L:24D), (c) short photoperiod (08L:16D) and (d) long photoperiod (16L:08D), as well as to three relative humidity regimes: (a) low (40% RH), (b) medium (60% RH) and (c) high (70-80% RH). Data revealed that relative humidity is not a significant predictor of diapause termination, but it affects the post-winter developmental period. Higher relative humidity promotes post-winter pupae development. On the other hand, photoperiod significantly affected both diapause termination and post-winter development of R. cerasi pupae. Light conditions (24L:00D) accelerate adult emergence, particularly for females. Regardless of the photoperiod (24L:00D, 00L:24D, 08L:16D), rates of adult emergence were high (>75%) for chilling intervals longer than 6.5 months. Nonetheless, exposure to a long day photoperiod (16L:08D), during chilling, dramatically reduced the proportion of adult emergence following 6 months exposure to chilling. Our findings broaden the understanding of factors regulating diapause responses in European cherry fruit fly, local adaptation and synchronization of adult emergence with the ripening period of major hosts. Copyright © The Author(s), 2020. Published by Cambridge University Press

Addressing climate change impacts on agriculture: Adaptation measures for six crops in Cyprus

The agricultural sector of Cyprus is seriously affected by climate change impacts. In the framework of the ADAPT2CLIMA project, the available techniques and methods implemented worldwide for the adaptation of six crops (wheat, barley, potatoes, tomatoes, grapes, and olives) to climate change impacts were thoroughly assessed. The identified adaptation options were categorized according to the climate change impact they address as follows: measures against drought stress, heat stress, decreasing plant health, extreme weather events and reduced crop productivity. Another category that refers to measures that address more than one category of climate change was also added. The evaluation of the identified adaptation options was based on a self-administered semi-structured questionnaire. The identified adaptation measures were graded according to the following criteria: efficiency of the measure, urgency of implementing the measure, usefulness of implementation irrespective of climate change, technical difficulty, contribution to climate change adaptation, economic viability and social acceptance. Fifty-six respondents (experts and stakeholders) filled the questionnaire, suggesting twelve recommended adaptation measures (with high score ≥ 60%), which mainly refer to irrigation adaptation measures, cultural practices, and methods for upgrading external services to farmers. The recommended adaptation measures for Cyprus are thoroughly presented and discussed. © 2020 by the authors

Evaluation of mass trapping devices for early seasonal management of ceratitis capitata (Diptera: Tephritidae) populations

Mass trapping is an environmentally safe alternative to insecticide application for the Mediterranean fruit fly management. The selection of effective trap-attractant combinations for monitoring and mass trapping control remains challenging. The current study explored the attractiveness of trapping devices during spring (early season) and summer (late season) in field cage trials. Five trapping devices were assessed: (a) the commercially available Decis® trap, (b) Tephri trap baited with Biodelear, (c) Tephri trap baited with BioLure, (d) International Pheromone McPhail trap (IPMT) baited with Biodelear, and (e) IPMT baited with BioLure. On a test day, 100 adults (50 males and 50 females) were released in each field cage wherein traps were placed individually. Trap captures were recorded at hourly intervals from 10:30 am to 5:30 pm. Our results showed that Tephri traps baited either with BioLure or Biodelear captured the most adults under low temperatures. Efficacy of Tephri traps baited with BioLure were higher than that of other trap-attractant combinations at high temperatures. Adult captures in Decis® trap were low during both seasons. More males than females were captured at low temperatures. Both efficacy and female selectivity of trapping devices are related to prevailing temperature regimes during spring and summer under semi-field conditions. © 2021 by the authors

Old residents and new arrivals of Rhagoletis species in Europe

The genus Rhagoletis (Diptera: Tephritidae) comprises more than 65 species distributed throughout Europe, Asia and America, including many species of high economic importance. Currently, there are three Rhagoletis species that infest fruits and nuts in Europe. The European cherry fruit fly, Rhagoletis cerasi (may have invaded Europe a long time ago from the Caucasian area of West Asia), and two invasive species (recently introduced from North America): The eastern American cherry fruit fly, R. cingulata, and the walnut husk fly, R. completa. The presence of different Rhagoletis species may enhance population dynamics and establish an unpredictable economic risk for several fruit and nut crops in Europe. Despite their excessive economic importance, little is known on population dynamics, genetics and symbiotic associations for making sound pest control decisions in terms of species-specific, environmental friendly pest control methods. To this end, the current paper (a) summarizes recently accumulated genetic and population data for the European Rhagoletis species and their association with the endosymbiont Wolbachia pipientis, and (b) explores the possibility of using the current knowledge for implementing the innovative biological control methods of sterile insect technique and incompatible insect technique. © Copyright Cambridge University Press 2019