Overwintering and seasonal dynamics of spotted wing drosophila, D. suzukii, in the Okanagan-Columbia River basins, USA and Canada, 2010-2014

Introduction: Adult spotted wing Drosophila, Drosophila suzukii, were monitored at 367-686 trap sites per year, 2010-2014, using traps with lures of apple cider vinegar or yeast. The traps were placed in various crops and non-crop locations, across 137,500 km2 of the Okanagan and Columbia River Basins in Oregon, Washington, USA, and British Columbia, Canada.
Methods: Trap records were subjected to a spatially explicit analysis using a geographic information system (GIS). Results are presented for berry, cherry, stone fruit, grape, non-crop host plants, and non-host sites and for conventional, organic, backyard, and feral sites by region and year. After removal of duplicate traps, at each site we calculated Daymet daily weather (from NOAA), 25 geomorphometric layers (SAGA software), and the distances to water, and other spatial variables for each site using Spatial Analyst toolbox (ESRI).

Results/Conclusion: Emergence from overwintering (week of first catch of D. suzukii) in 2010-14 was highly related (R2=0.49) to year, pesticide treatment, and number of winter days with temperatures <-5 °C, in 1505 site-years of records from cherry trees, in a spatially explicit statistical analysis. Similarly, emergence from overwintering in 2011-14 was significantly related (R2=0.42) to the year, pesticide treatment at the site, logarithm of the prior year population of D. suzukii during the Fall, latitude, elevation, and topographic wetness index, in 1136 site-years of records from berry, cherry, stone fruit and grape habitats. The results are leading to improved understanding of the ecology of this invasive insect and informed management strategies.