Factors influencing soybean aphid mortality during rainstorm events

Rainstorm events have regularly been observed to negatively impact the populations of small soft bodied insects in cropping systems, though it is not clearly understood which factors affect population reduction during rainstorms. Soybean aphid, Aphis glycines Matsumura, is an invasive pest species that regularly infests soybean crops in the Midwest and has been reported to experience population declines in the wake of rainstorm events. A field study was conducted to identify potential factors responsible for rainstorm related soybean aphid mortality in commercial soybean fields throughout western Minnesota during the 2010 and 2011 growing seasons. Factors observed for the study included, average soybean aphid pre-rain count by plot, soil type, visit in the count series, soybean plant stage, average daily wind speed, maximum sustained daily wind speed, total rainfall, and rain-wind interactions. Data was collected in 11 fields, with 4-10 randomly selected plots in each field. Destructive aphid counts were taken at each plot before and after the arrival of rainstorm events. Weather data was collected through NOAA records and two Rainwise MK-III-LR weather stations. Data was collected from a total of 188 plots located in 11 fields throughout western MN. Data was analyzed using a multiple regression analysis in SAS software with proportion aphid survival serving as the dependent variable. Preliminary analyses indicate that soil type, soybean plant stage, maximum sustained daily winds, and rain-wind interactions significantly influenced (P<0.05) aphid mortality.