Effect of Light on the Activity Rhythm of Adult Soybean Pod Borer, Leguminivora glycinivorella (Lepidoptera: Tortricidae)

The locomotor activity of unmated adult Leguminivora glycinivorella (Matsumura) (Lepidoptera: Tortricidae) immediately after emergence was recorded under various photoperiods using an actograph in an incubator. Under a 12L : 12D photoperiod, both sexes displayed an approximately 24-hour cycle rhythm consisting of active and resting periods. Activity was observed around switching from the light to dark period. Under constant dark conditions, rhythms similar to those in the 12L : 12D photoperiod were observed, indicating that the activity is controlled by a circadian clock. The activity phase receded as the beginning of constant darkness was delayed, and the beginning of constant darkness was almost coincident with the median of activity, suggesting that the light stimulus that switches from light to dark is a zeitgebers of the circadian clock. Under constant light conditions, three out of five males and two out of five females were found to have lost their periodicity. Even in the individuals that showed periodicity, there was a significant decrease in 24-hour activity in males and a loss of rhythm after the second day of emergence in females, suggesting that constant light conditions disrupt the circadian clock. Artificial light irradiation at night may suppress mating behavior in soybean fields, leading to damage suppression.