Male-Biased Capture in Light Traps in Spodoptera exigua (Lepidoptera: Noctuidae): Results from the Studies of Reproductive Activities

Abstract

Nocturnal insects show phototactic behavior. Interestingly, males are caught by light traps more often than females in many species. In the present study, the male-biased capture in light traps in the field was evaluated to test the hypothesis that male-biased capture was associated with the reproductive activities of Spodoptera exigua. During a 16-wk. period in 2011, a total of 5075 moths caught by light traps in the field revealed a significant male-biased capture. However, the sex ratio of the natural population was not significantly different from 1:1 from July to October 2011. The ratio of moths caught per hour by light traps showed that females were captured in the first half of the night, whereas the peak capture by light traps for males occurred in the second half of the night. Among the captured adults, the percentage of unmated females was significantly lower than that of the mated females and males. Experiments in the laboratory indicated that the time of activities for both sexes was consistent with the active patterns of oviposition and copulation. The percentage of flight-to-light of the unmated females was significantly lower than that of the mated females and males. Thus, the lower capture of the unmated females, which is associated with reduced positive phototactic responses of S. exigua, probably is one of the reasons resulting in the male-biased sex ratio in light traps.