Abstract
To clarify the seasonal change in the dispersal ability of the two-striped leaf beetle, Medythia nigrobilineata, the occurrence and ovarian development of adult insects were investigated in soybean fields in Miyagi Prefecture, Japan. Soybean seedling traps were installed from April to May before the germination of soybean seeds sown in the fields. Overwintered adults were observed in the traps from late April to early May, about one month before the normal germination of soybean. Two methods were used to collect insects: tapping on soybean plants and the use of sticky traps set in the soybean fields. The number of adults of the 1st generation captured using sticky traps was smaller than for overwintered and 2nd generations. Among the overwintered generation, female adults collected on the soybean seedlings had developed ovaries and mature eggs, whereas the adults captured using sticky traps had poorly developed ovaries. Female adults of the 1st generation collected both by tapping on soybean plants and by using sticky traps had developed ovaries. The ovaries of the female adults of the 2nd generation were immature, showing no difference between the collection methods used. The sex ratio of the adults captured using sticky traps showed no significant difference from that of adults collected by tapping on soybean plants. These results suggest that immature adults have high flight activity, and that overwintered and 2nd generation adults are involved in the flight dispersal of the species.
