Article written by Will Pradel, Jay DeLacy, Mary Rogers of the University of Minnesota.
Spotted-wing drosophila (SWD) is an invasive insect pest of soft-skinned fruits such as raspberry, blackberry, blueberry, strawberry, and cherry. Originally from Southeast Asia, SWD is a major pest of small fruit in Minnesota.
The detection of the parasitoid wasp, Leptopilina japonica, on and around two organic berry farms in Minnesota may have implications for the management of SWD, potentially reducing SWD populations. More details below.
What is Leptopilina japonica?
- L. japonica is a very small, non-stinging wasp that attacks SWD inside fruit.
- This parasitoid has now been found on fruit farms in Minnesota, indicating localized establishment.
- Field sampling also showed that L. japonica is commonly found in nearby wild and unmanaged areas, such as wooded edges and field borders, where non-crop SWD host fruits, such as honeysuckle, are present.
- L. japonica may be contributing to SWD suppression on farms.
Images: An SWD egg within a blueberry (left) and L. japonica adult (right).
What was found in Minnesota?
During the summer of 2024, we sampled fruit, baited SWD traps, and sticky cards at two organic blueberry farms in Northfield and Hastings, MN
L. japonica was recovered from fruit samples, traps, and sticky cards at both farms. More than 700 individual wasps were collected across the two sites.
Because L. japonica was detected using multiple sampling methods and at more than one location, the results indicate that this parasitoid is established in southeast Minnesota.
Why does this matter for growers?
L. japonica may be helping to naturally suppress SWD populations on and around fruit farms.
However, this study only shows that the parasitoid is present and established. It does not yet show how much SWD control it provides or whether it reduces fruit damage.
For now, L. japonica should be viewed as a beneficial insect that may contribute to SWD suppression, rather than a stand-alone management tool.
An important note about conservation
L. japonica is likely to be negatively affected by insecticide applications used to manage SWD, such as spinosad and other broad-spectrum products.
To help conserve this beneficial parasitoid:
Avoid unnecessary sprays when SWD pressure is low
Use lower-risk insecticides when possible, and
Consider the role of nearby field edges and wild host plants, which appear to support L. japonica populations.
Bottom line for Minnesota fruit growers
L. japonica, a small, non-stinging parasitoid wasp that attacks SWD larvae, has now been confirmed in Minnesota, with localized establishment in the southeastern region. As a result, it may assist in SWD management by providing natural suppression. Therefore, practices that reduce unnecessary insecticide use can help conserve this beneficial insect. However, growers will still need to monitor and manage SWD.
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