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.

In recent years, there has been an increase in the adventive establishment and spread of parasitoid wasps outside of their native range. However, lack of taxonomic tools can hinder the efficient screening of field-collected samples to document the establishment and range expansion of parasitoids on continent-wide geographic scales. Here we report that Leptopilina japonica (Hymenoptera, Figitidae), a parasitoid of the globally invasive fruit pest Drosophila suzukii (Diptera, Drosophilidae), is now widespread in much of North America despite not having been intentionally introduced. Surveys in 2022 using a variety of methods detected L. japonica in 10 of 11 surveyed USA States and one Canadian Province where it was not previously known to occur. In most surveys, L. japonica was the most common species of D. suzukii parasitoid found. The surveys also resulted in the detection of Ganaspis cf. brasiliensis (Hymenoptera, Figitidae), the recently-released biological control agent of D. suzukii, in six USA States where it had not previously been found. These new detections are likely a result of intentional biological control introductions rather than spread of adventive populations. A species-specific multiplex PCR assay was developed as a rapid, accurate and cost-effective method to distinguish L. japonica, G. cf. brasiliensis, the closely-related cosmopolitan parasitoid Leptopilina heterotoma (Hymenoptera, Figitidae) and other native parasitoid species. This dataset and the associated molecular tools will facilitate future studies of the spread and ecological impacts of these introduced parasitoids on multiple continents.

Drosophila suzukii (Matsumura) is native to East Asia but has widely established in the Americas and Europe, where it is a devastating pest of soft-skinned fruits. It has a wide host range and these non-crop habitats harbor the fly which then repeatedly reinvades crop fields. Biological control in non-crop habitats could be the cornerstone for sustainable management at the landscape level. Toward this goal, researchers have developed or investigated biological control tactics. We review over 100 studies, conducted in the Americas, Asia and Europe on natural enemies of D. suzukii . Two previous reviews provided an overview of potential natural enemies and detailed accounts on foreign explorations. Here, we provide an up-to-date list of known or evaluated parasitoids, predators and entomopathogens (pathogenic fungi, bacteria, nematodes, and viruses) and summarize research progress to date. We emphasize a systematic approach toward the development of biological control strategies that can stand alone or be combined with more conventional control tools. Finally, we propose a framework for the integrated use of biological control tools, from classical biological control with host-specific Asian parasitoids, to augmentative and conservation biological control with indigenous natural enemies, to the use of entomopathogens. This review provides a roadmap to foster the use of biological control tools in more sustainable D. suzukii control programs.

A major challenge to the area-wide management of Drosophila suzukii is understanding the fly’s host use and temporal dynamics, which may dictate local movement patterns. We determined D. suzukii’s seasonal host use in California’s San Joaquin Valley by sampling common crop and non-crop fruits in a temporal sequence of fruit ripening. We then evaluated the suitability of selected fruits as hosts. Drosophila suzukii emerged from both intact and damaged cherries during the cooler, early season period. Fly density remained low through the hot spring–summer period and re-surged as temperatures lowered in fall when the fly did not cause damage to intact peach, nectarine, plum, pear, grape, pomegranate, apple, persimmon and citrus (in order of ripening) but did emerge from the damaged fruits of these crops. The fly also emerged from two ornamental fruits (loquats and cactus) but was not found on wild plum and two endemic wild fruits (buckthorn and bitter berry). Drosophila suzukii completed development (egg to adult) on cactus, mandarin carpel, pomegranate seed, wild plum and buckthorn at survival rates similar to cherry (51.2–68.8%), whereas it had a lower survival rate on bitter cherry (33.2%), table grape (31.5%), raisin grape (26.5%), and wine grape (4.5%). The high acidity levels of grapes negatively affected the fly’s fitness. Among 10 cherry cultivars, survival rate was not affected by sugar content, but it decreased with increasing egg density per gram of fruit. Results suggest that in California’s San Joaquin Valley, the early season crops are most vulnerable, summer fruits ripen during a period of low pest pressure, and late season fruits, when damaged, serve to sustain D. suzukii’s populations in this region.