Winter ecology of Pardosa pseudoannulata (Bosenberg et Strand) in the paddy field under the sustainable agriculture on Iriomote Island, Okinawa Prefecture (In Japanese)

Abstract

A survey on the winter ecology of Pardosa pseudoannulata was made in the paddy field on Iriomote Island, Okinawa Prefecture in 1996 and 1997, in order to obtain basic knowledge of this spider and to use it as a useful natural control agent of paddy pests. The paddy field in which the present investigation was made had been maintained for the last 3 years under sustainable agriculture. The results obtained are summarized as follows: (1) Pardosa pseudoannulata overwintered in the paddy field at various stages, from young to adult, even bearing an egg-sac. They showed predation behavior even in mid-winter. (2) The population density of this spider in the paddy field during winter was estimated to be 1.0 per 1 m2 using the Petersen Method. (3) It was revealed that an uncultivated paddy field offered a good overwintering habitat for many insects, especially Diptera, Hemiptera-Homoptera, Thysanoptera, and spiders. Paddy pests such as Nephotettix apicalis, N. virescens and N. cincticeps, as well as some species of spiders other than P. pseudoannulata were included. (4) One P. pseudoannulata spider was estimated to eat 5-6 individuals of Nephotettix apicalis a day on average in February. (5) This spider has two peaks in its daily activity, i.e., in the morning (08:00-10:00) and in the evening (17:00-18:00). It is suggested that this spider acts more vigorously in lower rather than in higher luminous intensity. (6) Trigonidium haani, Euparatettix insularis, Gryllidae spp., Blattellinae spp., Misumenops tricuspidatus, Collembolans (Onychiuridae spp.) and P. pseudoannulata were recorded as prey of P. pseudoannulata in winter. This spider ate Collembolans frequently in the evening near water when plant-hoppers were less abundant. (7) It is suggested that P. pseudoannulata as well as other predatory insects are important as the control agents of paddy plant-hoppers in winter.