Ecological studies of Pirata subpiraticus (BÖESENBERG et STRAND) (Araneae: Lycosidae) II

Abstract

The life history of Pirata subpiraticus (BÖS. et STR.), was one of the major spiders in East Japan paddy fields, was examined under laboratory conditions.The young spiders that dispersed from the mother's back were reared until maturity, provided the adults of Dorosophira melanogaster and Psilopa spp. as preys, at a constant temperature of about 25°C with 10 hours of daylight.The spiders of the summer generation moulted 5 to 7 times and required an average of 62.7±13.1 days to mature, but the winter nymphs which were collected from paddy fields in October moulted 8 times and required 160.0±8.3 days under the same rearing condition (Table 1). The cause of the significant difference of developmental periods between both generations was not clear. But, this difference may suggest the diapause of winter nymphs of P. subpiraticus that induced by the exposure of the mothers or the eggs to low temperature and short daylength.The carapace widths of the nymphs were measured after each moulting of the winter generation (Table 2). As the carapace widths overlapped between some instars it was impossible to decide the instar by the measurement of the carapace width.The daily food consumption in the immature stages of this species was examined in the summer generation. High predation appeared in the second to forth day after moulting in all instars (Fig. 1). Total food consumptions in each instar increased with advance of the stage, and an average of about 40 flies were killed in the last instar.The daily food consumption of adult females showed 3 peaks occurring after dispersal of the young spiders from the mother's back (Fig. 2 and 3). The peak of food consumption after copulation, however, did not appear when the females mated just after the peak of post-moulting. In cases where other preys than flies were provided, the daily food consumption of these spiders also are described (Table 3-5).