Parasitoids depend on a series of adaptations to the ecology and physiology of their hosts and host plants for survival and are thus likely highly susceptible to changes in environmental conditions. We analyze the effects of global warming and extreme temperatures on the life-history traits of parasitoids and interactions with their hosts. Adaptations of parasitoids to low temperatures are similar to those of most ectotherms, but these adaptations are constrained by the responses of their hosts. Life-history traits are affected by cold exposure, and extreme temperatures can reduce endosymbiont populations inside a parasitoid, eventually eliminating populations of endosymbionts that are susceptible to high temperatures. In several cases, divergences between the thermal preferences of the host and those of the parasitoid lead to a disruption of the temporal or geographical synchronization, increasing the risk of host outbreaks. A careful analysis on how host-parasitoid systems react to changes in temperature is needed so that researchers may predict and manage the consequences of global change at the ecosystem level.

Although several species of the genus Cotesia are used in biological control programs against insect caterpillars throughout the world, little is known of their oviposition behavior. We describe here the types and distribution of antennal sensilla in Cotesia plutellae, a larval parasitoid of Plutella xylostella, and we analyze its oviposition behavior. Seven types of sensilla were found on both males and females. Only sensilla trichodea type II, with a putative contact chemoreceptive function, was significantly more abundant in females than in males, and its morphology and position on antennomeres were linked to the antennation behavior used by females during host search. We conclude that gustatory stimulus following antennal contact is probably the key stimulus inducing oviposition behavior. The sensilla type assumed to be implied in oviposition behavior was present in C. plutellae but not in two closely related species (C. glomerata and C. rubecula), which is discussed.

Because insects are ectotherms, their physiology, behaviour and fitness are influenced by the ambient temperature. Any changes in environmental temperatures may impact the fitness and life history traits of insects and, thus, affect population dynamics. Here, we experimentally tested the impact of heat shock on the fitness and life history traits of adults of the aphid parasitoid Aphidius avenae and on the later repercussions for their progeny. Our results show that short exposure (1 h) to an elevated temperature (36 degrees C), which is frequently experienced by parasitoids during the summer, resulted in high mortality rates in a parasitoid population and strongly affected the fitness of survivors by drastically reducing reproductive output and triggering a sex-dependent effect on lifespan. Heat stress resulted in greater longevity in surviving females and in shorter longevity in surviving males in comparison with untreated individuals. Viability and the developmental rates of progeny were also affected in a sex-dependent manner. These results underline the ecological importance of the thermal stress response of parasitoid species, not only for survival, but also for maintaining reproductive activities.

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Organisms are regularly subjected to abiotic stressors related to increasing anthropogenic activities, including chemicals and climatic changes that induce major stresses. Based on various key taxa involved in ecosystem functioning (photosynthetic microorganisms, plants, invertebrates), we review how organisms respond and adapt to chemical- and temperature-induced stresses from molecular to population level. Using field-realistic studies, our integrative analysis aims to compare i) how molecular and physiological mechanisms related to protection, repair and energy allocation can impact life history traits of stressed organisms, and ii) to what extent trait responses influence individual and population responses. Common response mechanisms are evident at molecular and cellular scales but become rather difficult to define at higher levels due to evolutionary distance and environmental complexity. We provide new insights into the understanding of the impact of molecular and cellular responses on individual and population dynamics and assess the potential related effects on communities and ecosystem functioning.

Temperature is both a selective pressure and a modulator of the diapause expression in insects from temperate regions. Thus, with climate warming, an alteration of the response to seasonal changes is expected, either through genetic adaptations to novel climatic conditions or phenotypic plasticity. Since the 1980s in western France, the winter guild of aphid parasitoids (Hymenoptera: Braconidae) in cereal fields has been made up of two species: Aphidius rhopalosiphi and Aphidius matricariae. The recent activity of two other species, Aphidius avenae and Aphidius ervi, during the winter months suggests that a modification of aphid parasitoid overwintering strategies has taken place within the guild. In this study, we first performed a field survey in the winter of 2014/15 to assess levels of parasitoid diapause incidence in agrosystems. Then, we compared the capacity of the four parasitoid species to enter winter diapause under nine different photoperiods and temperature conditions in the laboratory. As predicted, historically winter-active species (A. rhopalosiphi and A. matricariae) never entered diapause, whereas the species more recently active during winter (A. avenae and A. ervi) did enter diapause but at a low proportion (maximum of 13.4 and 11.2%, respectively). These results suggest rapid shifts over the last three decades in the overwintering strategies of aphid parasitoids in Western France, probably due to climate warming. This implies that diapause can be replaced by active adult overwintering, with potential consequences for species interactions, insect community composition, ecosystem functioning, and natural pest control.

Antennal sensilla were compared in females of two encyrtid Hymenoptera, Epidinocarsis lopezi and Leptomastix dactylopii, parasitoids of adults and larvae of Pseudococcidae. The external morphology of these sensilla was studied using scanning electron microscopy and their ultrastructure observed under transmission electron microscopy using ultrathin sections. Female antennae have seven different types of sensilla, morphologically very similar in the two species: trichoid sensilla, which are putative mechanosensilla, sensilla chaetica types 1 and 2, which are presumably contact chemosensilla, and sensilla chaetica types 3 and 4, basiconic sensilla, and placoid sensilla, which are all presumed to be olfactory sensilla. Sensilla chaetica types 2 and 4 are thought to be directly involved in host discrimination. The only differences between the two species are in the number and distribution of some types of sensilla. These differences might be related to the varied tritrophic ecological context of the two species rather than to their similar biology.

1. In the context of global change, modifications in winter conditions may disrupt the seasonal phenology patterns of organisms, modify the synchrony of closely interacting species and lead to unpredictable outcomes at different ecological scales. 2. Parasites are present in almost every food web and their interactions with hosts greatly contribute to ecosystem functioning. Among upper trophic levels of terrestrial ecosystems, insect parasitoids are key components in terms of functioning and species richness. Parasitoids respond to climate change in similar ways to other insects, but their close relationship with their hosts and their particular life cycle – alternating between parasitic and free‐living forms – make them special cases. 3. This article reviews of the mechanisms likely to undergo plastic or evolutionary adjustments when exposed to climate change that could modify insect seasonal strategies. Different scenarios are then proposed for the evolution of parasitoid insect seasonal ecology by exploring three anticipated outcomes of climate change: (i) decreased severity of winter cold; (ii) decreased winter duration; and (iii) increased extreme seasonal climatic events and environmental stochasticity. 4. The capacities of insects to adapt to new environmental conditions, either through plasticity or genetic evolution, are highlighted. They may reduce diapause expression, adapt to changing cues to initiate or terminate diapause, increase voltinism, or develop overwintering bet‐hedging strategies, but parasitoids' responses will be highly constrained by those of their hosts. 5. Changes in the seasonal ecology of parasitoids may have consequences on host–parasitoid synchrony and population cycles, food‐web functioning, and ecosystem services such as biological pest control.