The spotted wing drosophila (SWD), Drosophila suzukii, is an invasive fruit fly insect pest. Native to East Asia, it was first reported in California in 2008. Since then, the insect has migrated to other states including Alabama where it was discovered in 2010. Today, the insect exists in all 67 counties across the state.

A female spotted-wing drosophila (Drosophila suzukii).

The SWD poses serious threats to small fruit producers of blackberries, blueberries, cherries, elderberries, strawberries, and other fruit tree crops. Current control is mainly by pesticide application. However, recent information has shown that several parasitic wasps (good insects) will attack the SWD larvae. The most prominent among them are Ganaspis brasiliensis and Leptopilina japonica. These two parasitoids are reported in ten states, including Delaware, Georgia, Maine, Maryland, Michigan, New Jersey, New York, North Carolina, Oregon, and Pennsylvania, as well as the Canadian Province of Ontario. It was also confirmed in Washington State following initial detection in adjacent British Columbia, Canada in 2016.

Emergence of the Wasp

In August 2024, mature wild elderberries from Madison, Cullman, Morgan, Walker, and Winston Counties in Alabama were collected and incubated for SWD emergence. The elderberries were taken from plants along the roadside except for the berries harvested in Madison County. The Madison County berries were collected from a wooded area surrounding The People’s Patch, a farm near the campus of Alabama A&M University (AAMU).

Eighteen wasps were collected from the samples after incubating the elderberries for four weeks. Some of the samples were put in alcohol and sent to the USDA Systematic Entomology Laboratory in Beltsville, Maryland for identification. The samples were confirmed to be both male and female wasps (L. japonica). The finding may be the first L. japonica wasp report in Alabama.

Leptopilina japonica
(Photo credit: Kent Daane)

What is the Leptopilina japonica?

The L. japonica is a parasitic wasp native to East Asia, particularly Japan and Taiwan. It has been intentionally introduced to various regions, including North America and Europe, as a biological control agent against the SWD.

How does the wasp work?

This tiny wasp lays its eggs inside the larvae of the SWD. The wasp’s larvae feed on the SWD larvae, eventually killing them. By laying its eggs and finally killing them, the wasps reduce SWD populations, preventing damage to fruit crops.

Why is the SWD important to berry farmers?

The SWD has been causing significant crop losses in many fruit-growing regions. L. japonica offers a natural solution to control this pest without relying heavily on chemicals. The L. japonica is part of integrated pest management (IPM) practices (namely biological control), which aim to reduce the use of pesticides while maintaining healthy crop yields. Although we are seeing this insect for the first time in Alabama, we hope they have established well and are able to populate which will reduce the need for chemical control of SWDs, lowering production costs over time.

Current distribution map of L. japonica in the United States. Map is available under the Open Database License. Map taken from Gariepy, Tara D., Paul K. Abram, Chris Adams, et al. 2024. Widespread Establishment of Adventive Populations of Leptopilina japonica (Hymenoptera, Figitidae) in North America and Development of a Multiplex PCR Assay to Identify Key Parasitoids of Drosophila suzukii (Diptera, Drosophilidae). Neobiota 93: 63-90.

Next Steps

With recent funding from the Southern Sustainable Agriculture Research and Education, the Alabama Extension at AAMU’s IPM program will conduct a statewide survey to establish the importance of L. japonica and other parasitic wasps in reducing the SWD population in Alabama.

Monitoring this wasp and others will continue by collecting samples from different berry crops where the SWD has attacked berries, such as blueberries, blackberries, and strawberries. Again, mature berries will be incubated at room temperature to determine if the SWD and the wasp will emerge. This method helps determine the effectiveness of the wasp in reducing the SWD population. Findings will be reported to producers during the growing season.

For more information, contact Extension Integrated Pest Management Specialist Clement Akotsen-Mensah at (256) 372-4969.