Location: Invasive Species and Pollinator Health
Project Number: 2030-22000-033-008-S
Project Type: Non-Assistance Cooperative Agreement
Start Date: Sep 1, 2020
End Date: Aug 31, 2025
The emphasis in the first year of the project will be on setting up sites, and improving rearing of the parasitoid Ganaspis brasiliensis for mass release against spotted wing drosophila. Specific objectives are to: 1) select four site pairs for areawide implementation and control (companion site); 2) improve mass rearing of the imported parasitoid, G. brasiliensis; 3) test the impacts of G. brasiliensis on spotted wing drosophila in release cages; and 4) assess the efficacy of the sustainable areawide approach at the four implementation sites.
During Phase I of the project four candidate sites will be located in Watsonville, Santa Cruz Co., at Driscoll’s Berries and Naturipe. Site will include large acreages of organic fields of blackberry and raspberry adjacent to wild Himalayan blackberry. SWD populations and parasitism levels have been sampled here since spring 2017. Both Driscoll’s and Naturipe have participated in parasitoid releases and are enthusiastic partners. A site will be ~250 acres or larger and comprising 10-25% non-crop vegetation or woody areas. While selecting sites, each site will be scored for composition: average size of fields, non-crop vegetation, crop type, and phenology of crops. We will also select a companion site 1-3 km away to serve as the control site. While selecting sites, each site will be scored for composition: average size of fields, non-crop vegetation, crop type, and phenology of crops. Features will be compared between trial and control sites will be tested with treatment as a fixed effect, site pair as a random block effect and using an appropriate distribution (i.e., Poisson, lognormal, binomial). During Phase II, parasitoids will be released into each ‘implementation’ site. To prepare for mass releases, the imported parasitoid G. brasiliensis will be reared in at UC Berkeley. Parasitoid releases will start in late spring/early summer as fruits are infested and SWD larvae/pupae are present. About 20,000 parasitoids per month of each species will be distributed within each non-crop plot adjacent to berry fields. Releases will continue for six months. Sites will be monitored from May to October when SWD is most active. Sites will have 1 sample point per 10 acres, 50 samples for two 250 acre fields. Each sample point will include a Scentry SWD monitoring trap and 500 g fruit collection. Fruit will be incubated in the lab in vented containers for two weeks to count adult SWD emergence, a subset can be checked immediately for larvae by salt flotation. To assist growers with decision-making, weekly monitoring will occur before fruit ripening and when growers are actively managing SWD. Biweekly monitoring may occur at other less critical periods. (Note: adult trap and fruit samples from non-crop areas and during post-harvest can exceed 1000 SWD per sample. Sorting requires separating out other Drosophila, and female SWD must be identified by a serrated ovipositor since they do not have wing spots.) To assess efficacy, we will compare adult fly counts and larval infestation between implementation and control sites with generalized linear mixed models with treatment as the fixed effect, site pair as a random block effect with an appropriate distribution. During Phase II after parasitoid release, more intensive sampling will be conducted in transects into the field and along the border of the non-crop area to determine spatial and temporal trends. Parasitism will also be checked by placement of sentinel SWD larvae/pupae in non-crop and field areas to confirm continued activity of the parasitoids. To compare presence of natural enemies, sticky card or vegetation sampling will be conducted in grower fields.