Spatial Analysis of Seasonal Dynamics and Overwintering of Drosophila suzukii (Diptera: Drosophilidae) in the Okanagan-Columbia Basin, 2010–2014

Citation

Thistlewood, H.M.A., Gill, P., Beers, E.H., Shearer, P.W., Walsh, D.B., Rozema, B.M., Acheampong, S., Castagnoli, S., Yee, W.L., Smytheman, P. and Whitener, A. 2018. Spatial Analysis of Seasonal Dynamics and Overwintering of Drosophila suzukii (Diptera: Drosophilidae) in the Okanagan-Columbia Basin, 2010–2014. Environmental Entomology: nvx178-nvx178. doi:10.1093/ee/nvx178.

Plain language summary

A previously unknown small vinegar fly, similar to the Drosophila found on ripe fruits, was first found in western Canada in 2009 and has now invaded most Canadian provinces and many countries. Spotted wing drosophila has caused major changes in growing practices and increased environmental and production costs to producers of berries, sweet cherry, stone fruits, and home gardeners, because it attacks unripe fruits and berries, and multiplies in many native plants. An international research team, coordinated from Summerland, used as many as 828 traps annually, 2010-2014, to report its seasonal cycles and sex ratios in crops and wild plants across the Pacific Northwest. High populations built up pre-harvest in 4 of 5 years. Being from Asia, early assessments were that Canadian winters were too cold, and some regions too dry, for its survival. However, we showed that the fly overwintered in all regions and years, despite winter temperatures near -18°C. Overwintering success was variable and related for the first time to growing practices used in conventional agriculture, certified organic, backyard, or wild sites, and the number of winter days with temperatures of -5°C or above. It was also related to their population in the prior autumn, and other factors. The fly is now a permanent resident in irrigated crops and wild habitats, in dry regions with cold winters and hot dry summers. The results were used to develop short-term adaptive tactics on arrival of the invasive insect and are shaping long-term strategies for pest management and for biological control.

Abstract

Spotted wing drosophila, Drosophila suzukii (Matsumura) (Diptera: Drosophilidae), was monitored from 2010 to 2014 in 314–828 sites located in interior fruit-growing regions of OR and WA, United States, and BC, Canada, using traps baited with apple cider vinegar or sugar-water-yeast. Seasonal population dynamics and sex ratios were summarized for berry, cherry, stone fruit, grape, non-crop host plants, non-host sites, and for conventional IPM, certified organic, backyard, and feral sites, by region and year. Overwintering was detected in all regions and years, despite winter temperatures below −17°C. A spatial analysis was conducted using a Geographic Information System (GIS), daily weather data, geomorphometric measures of terrain, distance to water, and other variables, at each site. Overwintering success at a site, measured as Julian week of first capture of D. suzukii, was significantly related (R2 = 0.49) in cherry habitats to year, agronomic treatment, and number of winter days with temperatures >−5°C. In berry, cherry, stone fruit and grape habitats, 2011–2014, it was significantly related (R2 = 0.42) to year, agronomic treatment, the logarithm of peak population of D. suzukii in the prior autumn, latitude, elevation, and topographic wetness index. The results show that D. suzukii has adapted to exploit a succession of irrigated crops and feral habitats in mixed landscapes of a semi-arid region with cold winters and hot dry summers, and are shaping strategies for pest management and for biological control.

Publication date

2018-04-05