As the linear regression function of the cumulative catch of the searchlight trap for the three-year period was tentatively correlated with a prefectural economic injury level for soybean fields, it might be feasible to predict S. litura arrivals better than the pheromone trap. This suggests that soybean leaf damage is closely linked to the number of S. The coefficient of determination ( R 2) of linear regression between the cumulative catch numbers of the searchlight trap and the cumulative damaged leaves for the three-year period was much higher than that between the cumulative catch of the pheromone trap and cumulative damage.

Furthermore, the cumulative catch numbers of the two traps in August and September were linearly associated with cumulative damaged leaves in the same period in each year and in the three-year period. This temporal difference coincided with the estimated duration of the egg stage plus an assumed mating period. The raw catch numbers of the two trap types in August and September 20 preceded subsequent damage peaks by an average of 5.3 days. To determine the relationship between pest arrival and crop damage, trap catch numbers and the number of soybean leaves damaged by 1st-instar larvae were examined by separately comparing raw numbers and cumulative numbers. litura in a soybean field in southwestern Japan was preliminarily investigated using a searchlight trap in comparison to a pheromone trap at one location, from August to mid-October in 2016–2018. To understand the occurrence of soybean leaf damage, the dispersal of S. Thus, there is no accurate means of forecasting soybean damage, and insecticide is applied on the basis of farmers’ observations of actual damage in fields. Pheromone traps are used to monitor male adults, but the catch peaks do not always predict leaf damage in soybean fields. The common cutworm, Spodoptera litura Fabricius (Lepidoptera: Noctuidae) is a major pest of soybean.

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