Spotted-wing drosophila, Drosophila suzukii (Matsumura) (Diptera: Drosophilidae) is originally from Asia, and in the last decade it has become a global economic pest of small fruits and cherries. Growers have expressed strong interest in biological control and other sustainable tactics to reduce reliance on insecticides. Biological control of spotted-wing drosophila has been studied intensively, with over 75 research publications. Here, we are reporting current information on predators, parasitoids, pathogens (fungi, nematodes, bacteria, endosymbiotic bacteria, and viruses), and competitors of spotted-wing drosophila. When relevant for the natural enemy group, the discussion focuses on the impact each natural enemy has been observed to have in the field, how to optimize control, the efficacy of commercial products available, and options that may be available in the near future. Studies are summarized in tables that can be sorted by species, spotted-wing drosophila life stage targeted, outcomes, lab/field trials, and studies that examined residual activity, dose-dependent responses, or other effects.

Mechanisms responsible for the success or failure of agricultural diversification are often unknown. Most studies of arthropod pest management focus on enhancing natural enemy effectiveness. However, non‐crop plants can also change crop host quality by reducing or adding soil nutrients or water, and therefore improve or hamper pest suppression. Native perennial ground covers may provide food or habitat to natural enemies and, in terms of competition for soil nutrients or water, be more compatible with crop management than exotic annuals. We conducted a 3‐year vineyard study to examine the impacts of native perennial grasses on pests, natural enemies, crop plant condition and soil properties. We included three ground cover treatments: bare soil with a grower standard drip irrigation; native grasses with drip irrigation; and native grasses with drip irrigation as well as an additional flood irrigation to keep the grasses green and growing during the season. Numbers of leafhopper pests Erythroneura spp. decreased in both native grass treatments, where parasitism rates were higher. Vine petiole nitrate levels were lower in grass treatments, indicating competition for soil nitrogen, which is most often considered to be detrimental. Berry weight was higher in the irrigated treatment but did not differ between the bare soil and non‐irrigated grass treatment. Grape °Brix was similar in the bare soil and native grass treatments, suggesting native grasses did not compromise grape quality. In fact, leaf water stress was lower and soil moisture higher not only in the irrigated grass treatment but, at times, in the non‐irrigated grass treatment, compared with the bare soil treatment. Synthesis and applications. Our work shows that native grasses contribute to a reduction in vineyard leafhopper pests by reducing host quality through competition for soil nitrogen and providing food resources and/or habitat for natural enemies. Native grasses also improve soil water content and may be part of a water conservation program for perennial crops in dry climate regions.

Asobara japonica (Hymenoptera: Braconidae), Ganaspis brasiliensis and Leptopilina japonica (Hymenoptera: Figitidae) are Asian larval parasitoids of spotted wing drosophila, Drosophila suzukii (Diptera: Drosophilidae). This study evaluated these parasitoids’ capacity to attack and develop from 24 non-target drosophilid species. Results showed that all three parasitoids were able to parasitize host larvae of multiple non-target species in artificial diet; A. japonica developed from 19 tested host species, regardless of the phylogenetic position of the host species, L. japonica developed from 11 tested species; and G. brasiliensis developed from only four of the exposed species. Success rate of parasitism (i.e., the probability that an adult wasp successfully emerged from a parasitized host) by the two figitid parasitoids was low in hosts other than the three species in the melanogaster group (D. melanogaster, D. simulans, and D. suzukii). The failure of the figitids to develop in most of the tested host species appears to correspond with more frequent encapsulation of the parasitoids by the hosts. The results indicate that G. brasiliensis is the most host specific to D. suzukii, L. japonica attacks mainly species in the melanogaster group and A. japonica is a generalist, at least physiologically. Overall, the developmental time of the parasitoids increased with the host’s developmental time. The body size of female A. japonica (as a model species) was positively related to host size, and mature egg load of female wasps increased with female body size. We discuss the use of these parasitoids for classical biological control of D. suzukii.

Grape growers in California utilize a variety of biological, cultural, and chemical approaches for the management of insect and mite pests in vineyards. This combination of strategies falls within the integrated pest management (IPM) framework, which is considered to be the dominant pest management paradigm in vineyards. While the adoption of IPM has led to notable and significant reductions in the environmental impacts of grape production, some growers are becoming interested in the use of an explicitly non-pesticide approach to pest management that is broadly referred to as ecologically-based pest management (EBPM). Essentially a subset of IPM strategies, EBPM places strong emphasis on practices such as habitat management, natural enemy augmentation and conservation, and animal integration. Here, we summarize the range and known efficacy of EBPM practices utilized in California vineyards, followed by a discussion of research needs and future policy directions. EBPM should in no way be seen in opposition, or as an alternative to the IPM framework. Rather, the further development of more reliable EBPM practices could contribute to the robustness of IPM strategies available to grape growers.

Insect parasitoids can attack phylogenetically related hosts that share similar physiological properties and defense mechanisms and, more importantly, overlapping ecological niches. Here, host preferences of three parasitoids, Asobara japonica (Hymenoptera: Braconidae), Ganaspis brasiliensis and Leptopilina japonica (Hymenoptera: Figitidae), were examined on two closely related hosts, Drosophila suzukii and D. melanogaster (Diptera: Drosophilidae). Each parasitoid's rate of successful parasitism (or offspring survival) on these hosts was first compared in no choice tests. Results showed that A. japonica had higher parasitism levels than G. brasiliensis and L. japonica, and that offspring survival for all parasitoids was similar on both host species. Host preferences in choice tests were then compared, with each parasitoid presented with the two host species at different proportions of host abundance. None of the parasitoids showed host preference or host switching, even though these parasitoids have different degrees of host specificity, from more generalized (A. japonica) to more specialized (G. brasiliensis). Further examination of parasitoid olfactory responses showed all three parasitoid species were attracted to volatiles from fruit infested by either host species and showed no preference to either D. suzukii or D. melanogaster. Results suggest that the hosts' phylogenetical similarity and a lack of any obvious fitness costs for offspring survival may reduce host preference by these larval parasitoids. Keywords Biological control • Host range • Host selection • Invasive species • Spotted-wing drosophila Key message • The preference for two hosts (Drosophila suzukii and D. melanogaster) was assessed for three parasitoids (Asobara japonica, Ganaspis brasiliensis and Leptopilina japonica) • The parasitoids did not display a preference between these closely related hosts, nor host switching • All parasitoid species were attracted to volatiles from fruit infested by either host and none of the parasitoids showed a preference to different hosts • The results provide new insights for classical biological control and potential apparent competition between closely related hosts