Heat waves – extended periods of abnormally hot weather – are predicted to increase in severity and frequency under climate change. The severity of heat waves should impact communities and food webs through effects on performance of individual species and through changes in the strength of interactions between them. This study tested the effects of severity of simulated heat waves, with daily maxima of either 32°C or 40°C, on a tritrophic food web consisting of plants, Capsicum anuum, aphids, Myzus persicae and two parasitoids, Aphidius matricariae and Aphelinus abdominalis. Osmolarity of plant sap (concentration of dissolved solids) was highest under 40°C heat waves, suggesting the presence of secondary plant compounds involved with stress responses. Population growth of aphids was lower under heat waves (both 32°C and 40°C daily maxima), compared to environments with periodic hot days. Development time of parasitoids was longer under heat waves. Heat waves decreased the proportion of winged aphids in the population. When both parasitoid species were present, impacts on aphid populations were greater in heat wave environments than environments with periodic hot days. When either parasitoid species was by itself, heat waves did not affect the interaction between parasitoids and aphids. Numbers of A. matricariae were reduced in heat wave environments, whereas numbers of A. abdominalis were not. In addition to direct effects on individual species, we also obtained indirect evidence for the effects of heat waves on the bottom–up effects of plant stress compounds on herbivore performance, and on the strength of inter and intra‐specific competition. Our results demonstrate that heat waves could have important effects on community structure, and on important, community‐level processes such as intra‐guild interactions and trophic cascades.

Two species of larval parasitoids of the globally invasive fruit pest, Drosophila suzukii (Diptera: Drosophilidae), Leptopilina japonica, and Ganaspis brasiliensis (both Hymenoptera: Figitidae), were detected in British Columbia, Canada in 2016 and 2019, respectively. Both are presumed to have been unintentionally introduced from Asia; however, the extent of their establishment across different habitats with diverse host plants used by D. suzukii was unclear. In addition, there was no knowledge of the temporal dynamics of parasitism of D. suzukii by these two parasitoids. To address these gaps, we repeatedly sampled the fruits of known host plants of D. suzukii over the entire 2020 growing season in British Columbia. We documented the presence of L. japonica and G. brasiliensis and estimated the apparent percentage of D. suzukii parasitized among host plant species. Across a large region of southwestern British Columbia, both L. japonica and G. brasiliensis were found to be very common across a variety of mostly unmanaged habitats over the entire course of the season (May–October) in the fruits of most host plants known to host D. suzukii larvae. Parasitism of D. suzukii was variable (0–66% percent parasitism) and appeared to be time-structured. Our study demonstrates that the close association between the two larval parasitoids and D. suzukii that exists in Asia has evidently been reconstructed in North America, resulting in the highest parasitism levels of D. suzukii yet recorded outside of its area of origin.

Ecological niche models (ENMs) have been proposed and applied as tools for predicting the extent of exotic species invasion risk and for identifying areas at risk of invasion. Despite the acknowledged concern of relying on occurrence records of variable and (or) unknown quality, the effect of taxonomically uncertain occurrence records on ENMs has not been investigated. We first present a schematic model describing how taxonomic uncertainty could yield varying predictions of invasion potential depending on the spatial characteristics of all versus “reliable” occurrence records. We then explore the issue in more detail by way of a case study on the morphologically and taxonomically difficult yellowdevil hawkweed (Pilosella glomerata (Froel.) Fr.), which is invasive in North America. We compared the climate niche properties and ENM predictions of invasion risk by P. glomerata in North America among models based on (i) all available occurrence records and (ii) records that are taxonomically “reliable”. “Total” records yielded niche properties that were significantly more heterogeneous than reliable records, and consequently, the potential invasion range of P. glomerata based on total records was predicted to be substantially larger. Our results provide rare empirical evidence that vetting occurrence records for taxonomic reliability is of critical importance for niche modeling.

We provide recommendations for sampling and identification of introduced larval parasitoids of spotted-wing drosophila, Drosophila suzukii (Matsumura) (Diptera: Drosophilidae). These parasitoids are either under consideration for importation (aka classical) biological control introductions, or their adventive (presumed to have been accidentally introduced) populations have recently been discovered in North America and Europe. Within the context of the ecology of D. suzukii and its parasitoids, we discuss advantages and disadvantages of estimating larval parasitism levels using different methods, including naturally collected fruit samples and sentinel baits. For most situations, we recommend repeated sampling of naturally occurring fruit rather than using sentinel baits to monitor seasonal dynamics of host plant–Drosophila–parasitoid associations. We describe how to separate Drosophilidae puparia from host fruit material in order to accurately estimate parasitism levels and establish host–parasitoid associations. We provide instructions for identification of emerging parasitoids and include a key to the common families of parasitoids of D. suzukii. We anticipate that the guidelines for methodology and interpretation of results that we provide here will form the basis for a large, multi-research team sampling effort in the coming years to characterize the biological control and nontarget impacts of accidentally and intentionally introduced larval parasitoids of D. suzukii in several regions of the world.

Many populations are thought to be regulated, in part, by their natural enemies. If so, disruption of this regulation should allow rapid population growth. Such “enemy escape” may occur in a variety of circumstances, including invasion, natural range expansion, range edges, suppression of enemy populations, host shifting, phenological changes, and defensive innovation. Periods of relaxed enemy pressure also occur in, and may drive, population oscillations and outbreaks. We draw attention to similarities among circumstances of enemy escape and build a general conceptual framework for the phenomenon. Although these circumstances share common mechanisms and depend on common assumptions, enemy escape can involve dynamics operating on very different temporal and spatial scales. In particular, the duration of enemy escape is rarely considered but will likely vary among circumstances. Enemy escape can have important evolutionary consequences including increasing competitive ability, spurring diversification, or triggering enemy counteradaptation. These evolutionary consequences have been considered for plant–herbivore interactions and invasions but largely neglected for other circumstances of enemy escape. We aim to unite the fragmented literature, which we argue has impeded progress in building a broader understanding of the eco-evolutionary dynamics of enemy escape.