Landscape effects on seasonal abundance of Drosophila suzukii and its parasitoids in California cane berry fields

Authors: Hogg, Brian; DAANE, KENT - University Of California Berkeley

Submitted to: Agricultural and Forest Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/13/2024
Publication Date: 10/30/2024
Citation: Hogg, B.N., Daane, K.M. 2024. Landscape effects on seasonal abundance of Drosophila suzukii and its parasitoids in California cane berry fields. Agricultural and Forest Entomology. https://doi.org/10.1111/afe.12664.
DOI: https://doi.org/10.1111/afe.12664

Interpretive Summary: The invasive fruit fly spotted wing drosophila (SWD) has become a major pest of soft-skinned fruit crops (cherries, raspberries, strawberries, blueberries, etc.) in the Americas, Europe and North Africa. In many regions, management of SWD is complicated by the fly’s ability to feed on fruiting plants outside the crop and then move into crop fields from natural habitats in the spring. Control strategies must consider this movement of SWD. In California, natural habitats adjacent to commercial berry fields often contain wild blackberry, a potential host for SWD. We sampled SWD in commercial berry fields and adjacent natural habitat throughout the year, to determine whether natural habitat is a seasonal or year-round refuge for SWD, and whether numbers of SWD in berry fields are influenced by the surrounding landscape. We also sampled two parasitic wasps that attack SWD. Numbers of SWD were consistently higher in natural habitat, particularly in fall, and proportions of female SWD were highest in berry fields, indicating that females dispersed into berry fields at higher rates than males. SWD numbers in berry fields were higher and lower in more diverse landscapes in fall and early spring, respectively, possibly reflecting changing needs of SWD over time. Parasitic wasp numbers were also higher in natural habitat, and were positively affected by the amount of natural habitat and cropland in summer. Results indicate that natural habitats were a year-round refuge for both SWD and its parasitic wasps, and that the effects of the surrounding landscape on SWD can change over the seasons.

Technical Abstract: Spotted wing drosophila, Drosophila suzukii, has become a major pest of soft-skinned fruit crops in the Americas, Europe and North Africa. In many regions, D. suzukii management is complicated by the fly’s ability to persist on non-crop hosts and then invade or reinvade crop fields from surrounding natural habitats. Control strategies must consider this seasonal movement of D. suzukii. In California, non-crop habitats adjacent to commercial cane berry fields often contain wild blackberry (Rubus spp.), a potential overwintering host for D. suzukii. We sampled D. suzukii and its naturally occurring parasitoids (the pupal parasitoids Trichopria drosophilae and Pachycrepoideus vindemmiae) in commercial berry fields and adjacent non-crop habitat throughout the year, to determine whether non-crop habitat is a seasonal or year-round refuge for D. suzukii, and whether numbers of D. suzukii and its parasitoids in berry fields are dependent on the composition of the surrounding landscape. Numbers of D. suzukii adults were consistently higher in non-crop habitat, particularly in fall, and proportions of female D. suzukii were highest in berry fields, indicating that females dispersed more widely than males. The effect of habitat diversity on numbers of D. suzukii adults was positive in fall and negative in early spring, possibly reflecting differing habitat requirements of D. suzukii over time. Parasitoid numbers were also higher in non-crop habitat, and were positively affected by proportions of non-crop habitat and cropland in summer. Results indicate that non-crop habitats were a year-round refuge for both D. suzukii adults and its parasitoids, and that landscape effects on D. suzukii abundance in crop fields can change over the seasons.