Application of a High-Resolution Climate Model Dataset to Assess Habitat Suitability for Spotted Wing Drosophila in Southwest Idaho

As global climate change continues to produce large deviations from the normals of the 19th and 20th centuries, the agricultural sector will need to adapt to these changes in order to maintain yields and feed the global population. Crop selections, yield amounts, and pest management techniques may need to be adjusted to adapt. The Spotted Wing Drosophila (SWD) is a small fruit fly-like bug that can infest berries and stone fruit crops by burrowing into the fruit (at most points in the fruit’s lifecycle) and laying its eggs. These eggs will hatch and the larvae will burrow back out of the fruit. The fruit is then rendered unsellable through USDA markets. The duration of time for a generation of SWD to go from hatching to egg-laying is usually around two weeks, so several generations are likely in a growing season with suitable weather and climate conditions. SWD were first found in traps in west-central Idaho in 2012, after its range had been spreading through the broader Pacific Northwest for several years. Since then, it has been found in insect traps across the agricultural region in Southwest Idaho. If climate change patterns continue with higher temperatures for longer periods of the growing season, and an increase in the growing season length in general, this will provide more time and opportunity for SWD reproduction. This may manifest as the SWD having more suitable places to live and reproduce, and/or the SWD reproducing more generations per growing season in places that it has already been found. If there is an increase in acreage that is growing berries and stone fruits, this may also increase the presence of the SWD. Climate data, particularly the daily high and low temperatures can be used to assess the suitability of locations that the SWD has access to. Growing Degree Day values that are derived from daily high and low temperatures provide a proxy for suitable temperature ranges in which the SWD would be active and breeding. This study uses data from a high spatio-temporal resolution long term simulation with the Weather Research and Forecasting (WRF) model together with Oregon State University’s Integrated Pest Management’s (OPM) model for the SWD behavior expectations to estimate the SWD behavior within the local climate of Southwest Idaho. This study looks at changes in the cumulative growing degree day over the years 1987-2016, and how these changes could impact the expected breeding patterns of the SWD. With the growing season length increasing, the potential for a 6th generation now exists in the latter half of the 30 year span. Additionally, the amount of locations that reach degree day thresholds to support five full generations of SWD has nearly doubled in 30 years. This suggests that the SWD can become a much more of a problem for the agricultural sector in Southwest Idaho in the future.