1. Global climate change models predict an increase in the frequency and magnitude of extreme temperature events. These temperature events, heatwaves for example, will impact a wide range of physiological and behavioural processes, particularly in ectotherms, and may therefore influence interactions between species.2. Anti-predator responses may be more costly under more severe temperature regimes and therefore trait-mediated disturbance could lead to high mortality or reduced reproduction under extreme and fluctuating temperature regimes.3. We examined the impacts of extreme and fluctuating temperatures on traitmediated indirect interactions in an aphid-parasitoid community.4. In treatments that isolated the effects of trait-mediated disturbance from the effects of foraging parasitoids we found that an increase in both the amplitude and frequency of peak temperatures reduced aphid numbers and provided evidence that the cost of trait-mediated disturbance could increase under frequent periods of high temperature. Aphid dispersal also increased with more frequent periods of high temperature.5. In treatments where female wasps were allowed to freely forage (direct + traitmediated effects), there was no evidence that extreme and fluctuating temperatures influenced the wasp's foraging ability. Exposure to extreme fluctuating temperatures did not influence the offspring production of exposed wasps or the position of the mummies within the plots.

Summary1. Most trophic interaction theory assumes that all predators are an abstract form of risk to which prey respond in a quantitatively similar manner. This conceptualization can be problematic because recent empirical work demonstrates that variation in the responses of prey to different predators can play a key role in structuring communities and regulating ecosystem function. 2. Predator identity -the species specific response of prey to a predator -has been proposed as an ultimate mechanism driving the relative contribution of indirect effects in food webs; however few studies have explicitly tested this hypothesis. 3. This study explores the impact of predator identity on direct consumptive (CE) and nonconsumptive effects (NCEs), and on the relative contribution of indirect, density and traitmediated effects in trophic cascades within host-parasitoid communities. 4. We systematically compared the individual, host-parasitoid-plant interactions of two actively foraging parasitoid species with disparate foraging styles, one aggressive and one furtive, a common aphid host and plant. Our results demonstrate that the degree of risk aversion by prey to each particular predator species (i.e. predator identity) is a key factor driving the nature and strength of direct and indirect transmission pathways. 5. Both parasitoid species, in general, had a negative impact on plants. The magnitude of the aphid anti-predator dispersal response was positively correlated with plant infestation and plant damage. The qualitative effect of predator-induced infestation of new plants superseded the quantitative effects of predator-mediated reductions in aphid numbers. 6. The greatest indirect impact on plants was generated by the aggressively foraging parasitoid, and the strength of the aphids anti-predator response (a NCE) antagonistically traded-off with CEs due to an increased investment in attempting to capture risk-sensitized prey. In contrast, the furtive parasitoid did not elicit a strong anti-predator response, had little indirect impact on plants, but generated very high CEs due to the advantage of ovipositing into a sedentary prey population. 7. Our data suggest the responses of prey to different predatory cues may be an important mechanism driving the relative contribution of transmission pathways in trophic cascades. We conclude that predator identity is a key factor influencing the nature and strength of food web interactions.

Climate change is predicted to increase the occurrence of extreme temperature events. We constructed a stage‐structured Leslie matrix model with intra‐generational dynamics to explore the impact of extreme and fluctuating temperatures on host–parasitoid dynamics. We varied three temperature parameters to generate a range of temperature regimes that varied in their daily maximum temperatures, the number of warmer‐than‐average days and the autocorrelation of those warmer‐than‐average days. All three temperature parameters influenced host–parasitoid dynamics. Increasing the frequency of warmer than average days and the degree of autocorrelation only exerted significant impacts on host– parasitoid dynamics when daily maximum temperatures were sufficient to produce temperature‐dependent mortality. The effects of increasing autocorrelation of daily temperatures were dependent on the maximum daily temperatures and the frequency of warmer than average days. When daily maximum temperatures were severely warm, but the frequency of those severely warm days was low, increasing autocorrelation increased the probability that the aphids and parasitoids will persist, but when the frequency of severely warm days is increased, increasing autocorrelation decreases the probability that the populations will persist. These temperature phenomena exert significant effects on host–parasitoid dynamics in addition to those effects produced by changes in mean temperatures and warrant further investigation at the community level.

Generalist natural enemies play an important role in controlling soybean aphid, Aphis glycines (Hemiptera: Aphididae), in North America. Several sampling methods are used to monitor natural enemy populations in soybean, but there has been little work investigating their relative bias, precision, and efficiency. We compare five sampling methods: quadrats, whole-plant counts, sweep-netting, walking transects, and yellow sticky cards to determine the most practical methods for sampling the three most prominent species, which included Harmonia axyridis (Pallas), Coccinella septempunctata L. (Coleoptera: Coccinellidae), and Orius insidiosus (Say) (Hemiptera: Anthocoridae). We show an important time by sampling method interaction indicated by diverging community similarities within and between sampling methods as the growing season progressed. Similarly, correlations between sampling methods for the three most abundant species over multiple time periods indicated differences in relative bias between sampling methods and suggests that bias is not consistent throughout the growing season, particularly for sticky cards and whole-plant samples. Furthermore, we show that sticky cards produce strongly biased capture rates relative to the other four sampling methods. Precision and efficiency differed between sampling methods and sticky cards produced the most precise (but highly biased) results for adult natural enemies, while walking transects and whole-plant counts were the most efficient methods for detecting coccinellids and O. insidiosus, respectively. Based on bias, precision, and efficiency considerations, the most practical sampling methods for monitoring in soybean include walking transects for coccinellid detection and whole-plant counts for detection of small predators like O. insidiosus. Sweep-netting and quadrat samples are also useful for some applications, when efficiency is not paramount.

Galls of Diplolepis variabilis (Bassett) (Hymenoptera: Cynipidae) on their host plant Rosa woodsii Lindley (Rosaceae) support a diverse community of parasitoid and inquiline wasps that exploit the gall inducer and the gall itself. Here, we studied quantitative variation in local structure of the gall community in the Okanagan Valley of southern British Columbia, Canada, from the United States border north, to test the hypothesis that dispersal limitation would generate a distance decay in gall community similarity. We also explored gall community richness in relation to latitude, as the northern range limit of the gall inducer occurs within our study area. We found that gall communities exhibited strikingly similar composition across the study region, with most of the major inquilines and parasitoids present across the gall's range. However, the increased richness of rare parasitoid taxa near the northern range limits of D. variabilis generated a marginally significant positive relationship between gall community richness and latitude. Overall, our study suggests that dispersal constraints do not influence the composition of the Diplolepis Geoffroy gall community at regional scales, and that gall communities offer useful models for studying the association between community structure and range limits.

The stability of populations is a central, yet challenging concept in ecology. Here, we examine the stability of annual abundance for populations of nine native and four exotic lady beetle species (Coccinellidae) in a mixed landscape in Michigan, USA, over 23 yr. The species have similar life histories, live together in the same habitats, and have been disturbed by the sequential introduction of exotic lady beetle species. The publicly available dataset was collected in a diverse landscape of three forest habitats, four annual crop habitats with different intensities of management, and three perennial crops. Replicated 1‐ha plots were sampled weekly with yellow sticky cards during the summer season for each habitat, three plots for each of the three forest types and six plots for each of the seven crop habitats. We quantified stability for each species and each species by habitat combination, using three parameters: trends in abundance, persistence, and temporal population variability. The most abundant lady beetle species were more stable than the uncommon and rare species. Habitat generalists had more stable population dynamics than specialists, but habitat breadth was confounded with lady beetle abundance. Exotic and native species with similar abundances had similar levels of stability. Exotic species disrupted the native populations, leading to declines in abundance for eight of nine species and increased population variability for the native species. The abundances of exotic lady beetles rose quickly to the long‐term mean. Our findings support the hypothesis that populations exhibit species‐specific levels of stability, not greatly affected by stochastic variations in environmental conditions or by habitat characteristics. We also show that exotic species can decrease the stability as well as the abundance of native species in a community of lady beetles.

The identification of key species within multi-predator assemblages suppressing agricultural pests is paramount to the incorporation of predators into pest management plans. Generalist predators have strong impacts on population growth of soybean aphids (Aphis glycines, Hemiptera: Aphidae) in North America, but their relative influence may vary seasonally, and potentially interact with immigration of alate aphids following initial field colonization. Here we present the results of a season-long study in Minnesota that used cage manipulations to estimate weekly impacts of predation on field populations of soybean aphids, while concurrently quantifying alate aphid and predator densities. We used generalized linear models based on field level aphid and predator counts, and aphid counts on caged and uncaged experimental plants, to show that Harmonia axyridis (Coleoptera: Coccinellidae) was negatively associated with A. glycines abundance, even under alate immigration levels associated with aphid outbreaks, suggesting potential regulation of aphid populations. In contrast, two other common predators, Coccinella septempunctata (Coleoptera: Coccinellidae) and Orius insidiosus (Hemiptera: Anthocoridae), did not show patterns of association with aphid dynamics. We also show that A. glycines populations only have significant positive associations with the number of immigrating alatae on uncaged experimental plants that had higher alate densities than the field average. The negative effect of H. axyridis on aphid populations was also observed on uncaged experimental plants, suggesting that even high levels of alate aphid immigration did not disrupt predator suppression. These results add to the growing body of evidence demonstrating that even low numbers of certain generalist predators can effectively suppress pest populations in agroecosystems. In particular, our findings suggest that the abundance of both H. axyridis and alate aphids are critical to soybean aphid seasonal dynamics.

We evaluated the diversity and spatiotemporal emergence patterns of parasitoid wasp species in the genus Eurytoma Illiger (Hymenoptera: Eurytomidae) associated with leaf galls induced by Diplolepis variabilis Bassett (Hymenoptera: Cynipidae) throughout the Okanagan Valley, British Columbia, Canada. We collected D. variabilis galls throughout the region, recorded adult Eurytoma emergence times, extracted mitochondria DNA from a subset of the emergents, and used cytochrome c oxidase 1 and cytochrome b amplificons to assign sampled individuals to species. We also assayed for the bacterial endosymbiont Wolbachia to evaluate the incidence of thelytoky in Eurytoma. Eurytoma showed an extended emergence period and a significant right skew in male emergence. We recorded six Eurytoma species, one of which appears to be previously undescribed. The greatest diversity of Eurytoma species occurs in the north of the sampled area. Five of the six species showed Wolbachia infection in at least some individuals, and the most abundant and widespread species, Eurytoma imminuta Bugbee, showed high Wolbachia infection levels and an all-female population, which strongly indicates endosymbiont-induced thelytoky. Our results demonstrate that gall communities are locally variable, and we suggest that future studies be undertaken to quantify variation in community composition at more local scales than has been past practice.