Relationship between the cardinal direction of passive trap placement and the number of captured adults at hibernation sites of Halyomorpha halys (Hemiptera: Pentatomidae)

Abstract

Overwintering adults of Halyomorpha halys (Stal) enter passive traps placed at their hibernation sites in autumn. These traps, made by packing bundles of rice straw into containers, were placed facing the four cardinal directions at a hibernation site in Akita Prefecture, northern Japan. The relationship between cardinal direction and number of captured adults was investigated using data gathered from 2000 to 2013 to forecast the species’ population density. There were no significant differences in the mean number of captured adults among the directions. However, the proportions of adults captured in each direction changed annually, and the variability on the northern and southern sides tended to be larger than that on the eastern and western sides. In addition, the proportion of the total number captured on the southern side was significantly and positively correlated with mean daily maximum air temperature in October. On the basis of these observations, it appears that the proportions of adults captured by traps set in each direction change annually in response to the timing of the change in air temperature in October each year. Therefore, the trapping data gathered from any single direction alone would not be sufficient for more accurate forecasts of the overwintering population density of H. halys.