Aromatic border plants in early season berries do not increase parasitism of spotted wing drosophila, Drosophila suzukii.

BACKGROUND: The spotted wing drosophila, Drosophila suzukii Matsumura, is a South-East Asian vinegar fly that is a serious worldwide economic threat to the small fruit industry. Typical control consists of weekly pesticide applications, which can have nontarget effects, increase residual pesticides and lead to the development of resistance within pest populations. One potential alternate method of control is the planting of aromatic intercrops to attract the natural enemies of D. suzukii and/or repel the flies directly. We intercropped strawberry rows with flowering sweet alyssum or ryegrass-clover (control) to evaluate their efficacy at mitigating D. suzukii infestation through the attraction of two specialized larval parasitoids, Leptopilina japonica (Novkovic and Kimura) and Ganaspis brasiliensis (Ihering). RESULTS: Our study did not demonstrate any significant effect of sweet alyssum intercropping on the infestation rate of D. suzukii in strawberries or parasitism level. However, we found that advanced sampling date and recorded numbers of D. suzukii larvae and parasitoids were positively correlated, indicating higher populations at the end of the strawberry-growing season. CONCLUSIONS: Sweet alyssum intercrops did not reduce D. suzukii infestation rates or increase parasitism levels, likely due to low population numbers in early season berry varieties. Aromatic intercrops may be more effective for increasing pest control in later season crops. © 2022 Society of Chemical Industry.

Adventive Larval Parasitoids Reconstruct Their Close Association with Spotted-Wing Drosophila in the Invaded North American Range.

Two species of larval parasitoids of the globally invasive fruit pest, Drosophila suzukii (Diptera: Drosophilidae), Leptopilina japonica, and Ganaspis brasiliensis (both Hymenoptera: Figitidae), were detected in British Columbia, Canada in 2016 and 2019, respectively. Both are presumed to have been unintentionally introduced from Asia; however, the extent of their establishment across different habitats with diverse host plants used by D. suzukii was unclear. In addition, there was no knowledge of the temporal dynamics of parasitism of D. suzukii by these two parasitoids. To address these gaps, we repeatedly sampled the fruits of known host plants of D. suzukii over the entire 2020 growing season in British Columbia. We documented the presence of L. japonica and G. brasiliensis and estimated the apparent percentage of D. suzukii parasitized among host plant species. Across a large region of southwestern British Columbia, both L. japonica and G. brasiliensis were found to be very common across a variety of mostly unmanaged habitats over the entire course of the season (May-October) in the fruits of most host plants known to host D. suzukii larvae. Parasitism of D. suzukii was variable (0-66% percent parasitism) and appeared to be time-structured. Our study demonstrates that the close association between the two larval parasitoids and D. suzukii that exists in Asia has evidently been reconstructed in North America, resulting in the highest parasitism levels of D. suzukii yet recorded outside of its area of origin.