Abstract
Seasonal prevalence of the adult yellowish elongate chafer, Heptophylla picea, was examined by collecting the insects with light traps in the tea fields. The adults appeared from May 29 to June 23, reaching a peak number at about June 10. The ratio of the females to the total number of adults collected from the light traps was very low, only 0.1%, which was unexpected as the sex ratio of the chafer should be approximately 1:1. To elucidate the cause of this phenomenon the flight activity of the adults was observed in a field insect cage. The results showed that only 0-0.8% of the females flew in contrast with 25.0-35.4% of the males. Thereafter, the adults were forced to fly by using a tethered flight apparatus. Again, the flight ratio of the females was much lower than that of the males. Based on these results, it was concluded that the flying habit of the female chafers is almost inexistent which may occur for the fact that they could not be collected with light traps.
