The effect of temperature on host patch exploitation by an egg parasitoid

Abstract

The effect of temperature during host patch exploitation by parasitoids remains poorly understood, despite its importance on female reproductive success. Under laboratory conditions, we explored the behaviour of Anaphes listronoti, an egg parasitoid of the carrot weevil, Listronotus oregonensis, when foraging on a host patch at five temperatures. Temperature had a strong effect on the female tendency to exploit the patch: A. listronoti females parasitized more eggs at intermediate temperature (20 to 30°C) compared to those foraging at the extreme of the range (15.9°C and 32.8°C). However, there was no difference in offspring sex-ratio and clutch size between temperature treatments. Mechanisms of host acceptance within a patch differed between temperatures, especially at 32.8°C where females used ovipositor insertion rather than antennal contact to assess whether a host was already parasitized or not, suggesting that host handling and chemical cues detection were probably constrained at high temperature. Females spent less time on the host patch with increasing temperatures, but temperature had no effect on patch-leaving rules. Our results show that foraging A. listronoti females behave better than expected at sub-optimal temperatures, but worse than expected at supra-optimal temperatures. This could impair parasitoid performance under ongoing climate change.

Effects of phenological mismatch under warming are modified by community context

“…Thus, besides variation in developmental rates among temperatures, community contexts, and species, other factors contribute to differences in effects of phenological shifts across treatments. For example, preference and the ability to locate prey of different developmental stages of higher quality could also modify outcomes of host‐parasitoid interactions under warming (Augustin et al, 2021; Moiroux et al, 2015).…”

Bet-hedging in parasitoids: when optimization is not the best strategy to cope with climatic extremes

“…Anagrus delicatus can spread the risk of increased mortality by ovipositing fewer eggs in each patch even if more suitable hosts are available ( Reeve et al 1994 ). Augustin et al (2021) showed that patch time allocation in Anaphes listronoti Huber (Hymenoptera: Mymaridae) decreased when temperature increased, although the patch-leaving rules were not affected. In the context of climate change, even a single extreme unreliable event with strong temperature variation can have a major impact on host mortality, increasing the variability of host richness and/or travel times between patches.…”

Partial exploitation of host egg patches resulting from a high rejection rate of healthy hosts cautions the mechanistic use of functional response models

“…Empirical studies on the patch-leaving behaviour of egg and pupal parasitoids, motivated by the marginal value theorem, typically used a mass of hosts or a small area ( e.g., ≈ 1.5 cm 2 ) containing hosts as a patch of hosts (Field 1998; Wajnberg et al 2006; Augustin et al 2021; Zhang et al 2022). The marginal value theorem’s explanation for partial patch exploitation in these settings is related to functional response because within-patch parasitism is described by a functional response model.…”

“…However, given that hosts were located next to each other, it is difficult to consider that parasitoids left a patch because it was too difficult to find other hosts. In fact, direct observations of parasitoids in these studies revealed that parasitoids left a patch without parasitising healthy hosts that were physically encountered (Wajnberg et al 2006; Augustin et al 2021; Zhang et al 2022).…”