Abstract
Simple SummaryThe Asian cynipid gall wasp (ACGW) “Dryocosmus kuriphilus” has become widespread in Europe. In all invaded areas, it is parasitized by native parasitoids associated with oak galls, for which the ACGW represents a non-saturated adaptation space. Considering the increase in the frequency of extreme climatic events over the last twenty years (e.g., low temperatures during the vegetative period of the chestnut tree), this study aimed to elucidate the effects of cold stress on both ACGW biology and parasitism by native and introduced parasitoids. The ACGW–parasitoid system represents an ideal subject in which to evaluate the effect of sudden cold stress events due to the wasps’ biological characteristics, which include the ability to complete development even in galls detached from plants. We show that parasitism on and the mortality of ACGWs in three chestnut fields were affected by a cold treatment. Our results reveal species-specific differences in the abundance and performance of parasitoids associated with the ACGW in response to cold stress. For example, the frequency of Eupelmus spp. and Mesopolobus tibialis doubled as a result of the cold treatment in all three chestnut fields in both study years. Therefore, the plasticity in response to short-term temperature variation is associated with individual fitness in some parasitoid species.Temperature variation affects interactions involving plants, herbivores, and parasitoids, causing a mismatch between their phenological cycles. In the context of climate change, climatic factors can undergo profound and sudden changes, such as sudden hot or cold snaps. Herein, we show that the number of episodes of short but sustained low temperatures has increased, mainly during May, over the last two decades. We subjected galls induced by the Asian chestnut gall wasp (ACGW) Dryocosmus kuriphilus to cold stress to assess whether and, if so, how it affected the pest and its parasitoids. Over the course of two years, we measured seasonal parasitism, parasitism rates, the relative abundance of each parasitoid species, and ACGW mortality. We found that the cold treatment affected both the pest and the parasitoids, resulting in a reduction in the emergence of ACGWs and differing ratios of species within the parasitoid community. The most striking example was the change in the relative frequency of three species of Eupelmus spp. and Mesopolobus tibialis, which doubled in cold-stressed galls in all chestnut fields. The effects of temperature on the development of the host and the direct effects of cold temperatures on the surface of galls (in terms of the humidity or hardness of the galls) warrant further research in this direction.
Highlights
In the context of global climate change, climatic factors can undergo profound and sudden changes
We have shown that Asian chestnut gall wasp (ACGW) parasitism and mortality in the three chestnut fields were affected by the cold stress
Cold stress did not affect the composition of the parasitoid community in any chestnut field, which is consistent with the findings reported in [75], where no differences were found in the diversity, richness, or evenness of ACGW-associated species despite differences in their habitat
Summary
In the context of global climate change, climatic factors can undergo profound and sudden changes. The increase in the mean temperature is associated with climatic oscillations, such as heat and cold waves [1,2,3]. Modifications of abiotic factors, such as temperature variation, can act on different biological and evolutionary aspects [4,5], may disrupt the seasonal phenology patterns of organisms, and produce unpredictable changes in ecological niches of different insect groups [6,7], affecting, for example, the tri-trophic interactions involving plants, herbivores, and parasitoids [8]. Temperature variation can affect the phenology of both hosts and parasitoids [7,12,13], and asymmetric changes in the seasonal activities of closely interacting species are likely to be responsible for desynchronization in their lifecycles [8]
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