Climate change affects the abundance, distribution and activity of natural enemies that are important for suppressing herbivore crop pests. Moreover, higher mean temperatures and increased frequency of climatic extremes are expected to induce different responses across trophic levels, potentially disrupting predator-prey interactions. Using field observations, we examined the response of an aphid host-parasitoid system to variation in temperature. Temperature was positively associated with attack rates by parasitoids, but also with a non-significant trend towards increased attack rates by higher-level hyperparasitoids. Elevated hyperparasitism could partly offset any benefit of climate warming to parasitoids, and would suggest that higher trophic levels may hamper predictions of predator-prey interactions. Additionally, the mechanisms affecting host-parasitoid dynamics were examined using controlled laboratory experiments that simulated both temperature increase and drought. Parasitoid fitness and longevity responded differently when exposed to each climatic variable in isolation, compared to the interaction of both variables at once. Although temperature increase or drought tended to positively affect the ability of parasitoids to control aphid populations, these effects were significantly reversed when the drivers were expressed in concert. Additionally, separate warming and drought treatments reduced parasitoid longevity, and although temperature increased parasitoid emergence success and drought increased offspring production, combined temperature and drought produced the lowest parasitoid emergence. The non-additive effects of different climate drivers, combined with differing responses across trophic levels, suggest that predicting future pest outbreaks will be more challenging than previously imagined.

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Two saproxylic forest insects, Hylurgus ligniperda (F.) (Coleoptera: Scolytinae) and Arhopalus ferus (Mulsant)(Coleoptera: Cerambycidae), were reared on artificial or natural diet at 15 or 25°C to compare larval growth rates and survival. A significant diet by temperature interaction was observed in the growth of H. ligniperda larvae,which developed faster when reared on natural diet at 15°C, but grew faster and pupated significantly earlier when reared on artificial diet at 25°C. However, H. ligniperda survival by the end of the experiment was low on both diets when reared at 25°C (10.1%, 95% CI: 5.2–15.1%), which suggests that rearing at lower temperatures may be required. A. ferus larvae gained significantly larger body size when reared on artificial diet than on natural diet at both temperatures. Survival of A. ferus reared on artificial diet was significantly lower than larvae reared on natural diet at 25°C. The significant differences between A. ferus larval development rates when reared on artificial and natural diets preclude the use of artificial diet to collect meaningful data to construct temperature development models for ecological comparisons. Artificial diet provided a suitable medium for mass production of individuals for research purposes, e.g., test mortality in response to treatments. However, additional rearing studies are needed to determine whether the larger artificially reared larvae result in adults that are healthier, more productive, and live longer.

Hylurgus ligniperda (F.) and Hylastes ater (Paykull) are secondary bark beetles that have successfully spread beyond their native range, particularly into Pinus spp. plantations in the Southern Hemisphere. They feed on the phloem and cambial regions of highly stressed and recently dead Pinus spp. Here H. ligniperda and H. ater egg, larval, and pupal survival and development rates were modeled. Survival was variably influenced by temperatures depending on the life stage, but general trends were for H. ligniperda to tolerate warmer temperatures in comparison to H. ater. Nonlinear models showed 26, 29, and 34°C are the optimal temperature (maximum development rates) for the development of eggs, larvae, and pupae of H. ligniperda. In contrast, optimal temperature predictions were lower for H. ater, with estimates of 26, 22, and 23°C for the development of eggs, larvae, and pupae, respectively. H. ligniperda pre-imaginal stages were more tolerant to high temperatures, and H. ater pre-imaginal stages were more tolerant to low temperatures. Understanding the thermal requirements and limits for development for these two pests can assist in modeling emergence times, their current and potential species distribution and have potential phytosanitary applications.