Thermal ecology in a parasitoid attacking an adult life stage host: Recovery, sex effects and hidden costs of warming

Abstract

How climate change affects species interactions is a major issue in the field of ecology. Parasitoids play key ecological and economic roles as top-down controllers of herbivorous insect pests. A large body of research has shown that climate change disrupts host–parasitoid interactions, which can result in significant ecological shifts in the surrounding community (Kankaanpää et al., 2020; Malinski et al., 2023; Moore et al., 2021; Pardikes et al., 2022; Parker & Kingsolver, 2024; Schreven et al., 2017; Tougeron & Iltis, 2022; Wenda et al., 2023; Wu et al., 2016). However, most of this literature examines agriculturally relevant host–parasitoid systems, for example parasitoids of aphid or larval Lepidopteran hosts, and immature host life stages, for example egg, larva or nymph (Malinski et al., 2024). Because host life stages differ in mobility, sex, reproduction and other biological aspects, it is important to understand how climate change impacts host–parasitoid dynamics in parasitoids of different host life stages. The 2025 study by Baudino and colleagues (Baudino et al., 2025) brings much needed attention to the understudied system of adult host stage parasitism.

Baudino et al. (2025) examined the ecological outcomes of a host–parasitoid interaction between the braconid parasitoid wasp Dinocampus coccinellae and the invasive harlequin ladybird beetle Harmonia axyridis host across low (18°C), optimal (24°C) and high (30°C) temperatures. In this host–parasitoid system, D. coccinellae attacks adult hosts and uses a symbiotic RNA virus (D. coccinellae paralysis virus, DcPV) to induce temporary host paralysis prior to parasitoid emergence (Dheilly et al., 2015; Maure et al., 2011). After parasitoids complete development, some hosts recover normal feeding and reproductive behaviour, making host recovery a central life-history trait in this system. Host recovery is rare in host–parasitoid systems and therefore understudied: most existing reports are observational and seldom quantitative. By explicitly quantifying host recovery alongside other host and parasitoid fitness components, Baudino et al. (2025) add nuance and novelty to our understanding of host–parasitoid interactions and thermal ecology.

Consistent with patterns observed in most parasitoids, the authors found that elevated temperature proved detrimental to parasitoid success. While parasitoids frequently completed development at 18°C and, to a lesser extent, at 24°C, none successfully emerged at 30°C. This failure was driven primarily by increased mortality of late-instar larvae in the high temperature group, potentially resulting from parasitoid failure to exit the host body. Ontogenetic variation in thermal sensitivity is increasingly recognized as a key constraint on parasitoid fitness (Malinski et al., 2024; Moore et al., 2021, 2022; Valls et al., 2020), and this study is consistent with other work showing this late larval developmental timepoint may impose critical constraints on parasitoid thermal tolerance (Moore et al., 2022). Other relevant literature suggests that the sperm production stage of parasitoid development can function as a thermal constraint in different ways (Bressac et al., 2023; El-Sabrout et al., 2021). Additional work disentangling the mechanisms of high temperature disruption to host–parasitoid interactions across ontogeny is needed to improve predictions of climate change effects on parasitoid fitness and host population responses.

The phenomenon of host recovery from parasitism is a unique and understudied area of host–parasitoid ecology. Sex is rarely considered in studies of parasitoids attacking immature hosts, where it is often impossible to determine prior to eclosion. By working with adult hosts, this study reveals sex-specific vulnerabilities that may have important demographic consequences for host populations. Baudino et al. (2025) showed that host recovery probability was severely reduced at high temperatures, but this effect was difficult to assess given the low corresponding parasitoid survival at these temperatures. Interestingly, the researchers found an interaction between host sex and temperature on recovery of hosts, where the majority of infected females recovered at 18°C and 24°C, but in males this was only true for 24°C. Why are female hosts better able to recover at low temperatures than males? Authors discuss recovery as a function of the host's ability to suppress the DcPV in nerve tissues (Dheilly et al., 2015) and speculate on the biology of host sex as a potential mediator: high temperatures may impair the ability of host nerve cells to recover from viral infection, while lower energetic reserves in males could exacerbate recovery costs at low temperature (Davis et al., 2006). These hypotheses align with a broader body of work suggesting that parasitoid-associated symbionts, including viruses, may be a key vulnerability under heat stress which mediate thermal mismatches between hosts and parasitoids (Seehausen et al., 2017; Malinski et al., 2023). The mechanisms driving these interactive temperature-sex effects on host recovery, and the role symbionts play in these effects, warrant further investigation.

Testing these laboratory findings in field conditions is an important next step in this research. Dinocampus coccinellae frequently parasitizes overwintering ladybirds (Baudino et al., 2025), suggesting that phenology and heat exposure across the season may influence ecological outcomes. Additionally, further examination into the host–parasitoid thermal ecology of adult host life stages is needed to create a holistic understanding of parasitoid climate change biology. For example, in the D. coccinellae–H. axyridis system, hosts are paralysed by the DcPV, presumably eliminating behavioural thermoregulation and negating adult mobility effects on parasitism or host recovery. Whether parasitoids of adult hosts that do not induce paralysis show similar thermal sensitivities remains an open and intriguing question.

In sum, this important study addressed two broad gaps in host–parasitoid ecology. First, this research demonstrated how warming can alter host–parasitoid interactions in parasitoids of beetles and parasitoids attacking adult life stages, which are severely understudied relative to the dominance of Lepidopteran and aphid systems in agricultural contexts. Second, authors extend their study beyond typically lethal outcomes of parasitism and the narrow focus on host survival. By including parasitoid fitness metrics and the host trait of recovery, which may be central to population dynamics, the authors integrate multiple fitness components across both species to set a useful standard for future work. This work broadens our understanding of host–parasitoid thermal ecology and underscores the need to diversify the systems used to predict ecological responses in a rapidly warming world.

The author declares no conflicts of interest.

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