Habitat utilization by the giant water bug, Appasus (=Diplonychus) major (Hemiptera: Belostomatidae), in a traditional rice paddy water system in northern Osaka, central Japan

Abstract

To elucidate the seasonal pattern of habitat utilization by Appasus (=Diplonychus) major, a mark and recapture census was carried out. We categorized ten bodies of water for investigation into five categories: permanent pool, temporary pool, ditch, paddy and marsh, according to the water regime and vegetation structure. A total of 1,143 adults were marked, and 383 (34%) were recaptured more than once during the study period. Adults marked in June were recaptured in the same or the following month, while those marked between July and December were recaptured until the following July. The results show that A. major has a univoltine life cycle at the study site, overwintered adults reproduce in June and July, and adults of the new generation appear from July. Adults and nymphs of all instars were observed in all five types of waters, and the density was high in the ditch. Overwintering adults were observed on the moist ground of the drained paddy as well as in the water of the ditch. Overwintering adults had the ability to walk around and forage even in winter. A total of 50 movements of adults were observed among different types of waters, and adult movement was most frequent between April and July. The existence of different types of waters in the traditional rice paddy water system such as the study site was favorable for maintaining the population of A. major.