In the ongoing effort to manage the impact of the invasive fly pest spotted-wing drosophila (Drosophila suzukii), significant research has focused on two parasitoid wasps for use in biological control, including Ganaspis kimorum, shown here ovipositing in a D. suzukii larva in a blueberry. A new special collection in the Journal of Economic Entomology details a decade of advances in the use of these parasitoids and prospects for future research efforts to improve biological control strategies targeting spotted-wing drosophila. (Photo courtesy of Kent Daane, Ph.D., University of California, Berkeley, USA)

By Xingeng Wang, Ph.D.

Spotted-wing drosophila (Drosophila suzukii) is a global invasive pest of soft-skinned fruits, posing significant control challenges. An areawide approach, particularly biological control with specialized natural enemies like parasitoids, is crucial for reducing fly populations across diverse habitats. Research has focused on parasitoids, leading to the discovery of two key Asian larval parasitoids, Ganaspis kimorum and Leptopilina japonica, with the ensuing introduction and evaluation of G. kimorum in the United States and Europe and the adventive establishment of L. japonica.

A new special collection in the Journal of Economic Entomology highlights recent advances in biological control of spotted-wing drosophila, including early G. kimorum releases, L. japonica‘s adventive establishment, cold storage methods for G. kimorum, effective parasitoid sampling techniques, compatibility studies with entomopathogens, and insecticide impact assessments. A research roadmap is proposed to guide future biological control strategies.

Following regulatory approval in November 2021, G. kimorum was reared and released in Italy and the U.S. Wang et al. 2025 reported the first coordinated releases in three Mid-Atlantic states in 2022-2023, with successful overwintering observed. While initial recoveries and parasitism rates for G. kimorum remain low (<2%) in the U.S., it marks a first step in classical biological control. Rossi-Stacconi et al. 2025 showed that G. kimorum has also been recovered after overwintering in northern Italy, where continual release and monitoring showed its spread and increased parasitism rates over four years.

Successful G. kimorum release is critically dependent on cost-effective mass-rearing and cold storage protocols. Lisi et al. 2025 determined that storing G. kimorum at the pupal stage for two weeks at 10 or 15 degrees Celsius is ideal for scheduling production and synchronizing releases.

L. japonica was previously found adventively established in Canada, Europe, and several U.S. states. Recent monitoring in Washington, South Carolina, Michigan, and Mid-Atlantic states confirms its widespread presence (Beckwith et al. 2025, Czokajlo et al. 2025a, Van Timmeren et al. 2025, Wang et al. 2025). Van Timmeren et al. 2025 in Michigan found L. japonica emerging from spotted-wing drosophila on multiple non-crop plant species (e.g., blackberry, elderberry, pokeweed), with higher populations in unmanaged and organic blueberry plantings than commercial fields. Wang et al. 2025 detected L. japonica from D. suzukii on 16 of 30 host plants in Mid-Atlantic states, with parasitism rates up to 20% varying by season and host plant species. These studies underscore the importance of non-crop fruits as critical habitats for both the fly and its parasitoids, emphasizing the need to understand D. suzukii movement for areawide control (Hogg et al. 2025).

Developing effective sampling methods for parasitoids is crucial for assessing presence, post-release recoveries, and host-parasitoid associations. Traditional uninfested fruit traps are less effective than collecting D. suzukii-infested fresh fruit or using sentinel traps. Czokajlo et al. 2025b compared five methods, finding liquid lure traps (wine-vinegar or Scentry SWD lures) most effective for detecting G. kimorum and L. japonica quickly, though they yield many non-target specimens. Fruit sampling provides higher quality specimens and allows for parasitism rate determination but is labor-intensive. Lure traps predominantly catch female wasps, suggesting attraction to volatile compounds for egg-laying.

Naturally occurring resident parasitoids, primarily generalist pupal parasitoids like Pachycrepoideus vindemiae and Trichopria drosophilae, attack D. suzukii in the laboratory but show low field parasitism rates (<10%) (Daane et al. 2025). Common Drosophila larval parasitoids do not successfully develop in D. suzukii. While generalists can be reared on alternative hosts (Garcez et al. 2025), their control effectiveness is limited, shifting focus to key Asian larval parasitoids. Nevertheless, resident natural enemies contribute to conservation biological control, especially where specialized Asian parasitoids are not established (e.g., South America or regions like California lacking L. japonica) (Garcia et al. 2025). Proactive permitting for key Asian parasitoids is suggested.

Other biological control agents, including entomopathogens, nematodes, and predators, have been evaluated. Lee et al. 2025 showed that combining parasitoids (G. kimorum or L. japonica) with nematodes (Steinernema carpocapsae or S. feltiae) resulted in higher pest suppression, though nematode exposure reduced parasitoid emergence.

Bonneau et al. 2025 demonstrated that combinations of a pupal parasitoid (Muscidifurax raptorellus) and predators reduced D. suzukii in laboratory tests. These agents alone may be insufficient for field conditions, suggesting the need for integrated pest management (IPM) strategies incorporating methods like bioinsecticides.

Given the low consumer tolerance for damaged fruit, parasitoids alone are unlikely to suppress D. suzukii populations below economic thresholds. Pesticide use will remain necessary for marketable fruit. However, establishing larval parasitoids can suppress fly populations in unmanaged habitats, reducing pest pressure and the need for frequent sprays. This also benefits control of other insect pests by promoting natural enemies due to reduced insecticide use. It is crucial to select less risky pesticides; Tian et al. 2025 showed sublethal spinetoram concentrations decreased T. drosophilae parasitism. More studies are needed to optimize IPM strategies and conserve natural enemies.

After a decade, G. kimorum and L. japonica have established in parts of North America and Europe, with early efforts showcasing improved monitoring. However, G. kimorum is not yet widely established, and current parasitism rates are lower than those observed in Asia. The full impact of these biological controls is yet to be assessed. Future research should follow a proposed roadmap (Wang et al. 2025) prioritizing eight areas: advancing parasitoid establishment, understanding ecological factors (e.g., climate, habitat), assessing efficacy factors (e.g., host fruits, interactions), developing effective monitoring and impact evaluation methods, improving the impacts of adventive parasitoids (e.g., redistribution, augmentation), exploring genetic diversity, and integrating parasitoids with other biocontrol agents and IPM tactics. Exploring geographically diverse parasitoid populations is crucial to identify strains adaptable to various climate zones, aiming for resilient and effective biological control.

Finally, I would like to thank my fellow co-editors for this special collection: Paul K. Abram, Ph.D., Agriculture and Agri-Food Canada; Jana C. Lee, Ph.D., USDA-ARS Horticultural Crops Disease and Pest Management Research Unit; Cesar R. Rodriguez-Saona, Ph.D., Rutgers University; and Kent M. Daane, Ph.D., University of California Berkeley.

Xingeng Wang, Ph.D., is a research scientist at the U.S. Department of Agriculture’s Agricultural Research Service in the Beneficial Insects Introduction Research Unit in Newark, Delaware. Email: [email protected].