Seasonal life cycle of Zatypota albicoxa (Hymenoptera: Ichneumonidae), an ectoparasitoid of Achaearanea tepidariorum (Araneae: Theridiidae), in northern Japan
Abstract
The seasonal life cycle of Zatypota albicoxa (Walker, 1874), a koinobiont ectoparasitoid of the house spider, Achaearanea tepidariorum, was examined at Hirosaki (40°36′N), Japan. In winter, larvae were found on the abdomen of host spiders. They grew rapidly, emerged as adults in mid-May, and reproduced shortly after emergence. The seasonal occurrence of the developmental stages in the field indicated that this parasitoid is multivoltine in Aomori Prefecture.
Zatypota albicoxa (Walker, 1874) is a hymenopterous ectoparasitoid of the house spider, Achaearanea tepidariorum, and its relatives (Nielsen 1923; Hashimoto 1963; Hudson 1985; Fitton et al. 1987). Both eggs and larvae of this parasitoid develop on the abdomen of active spiders (Nielsen 1923). The fully grown larvae kill the host spider, and then spin cocoons on the host's web before pupation.
Although some observations on the behavior of this parasitoid have been reported (Nielsen 1923), little information is available on its seasonal life cycle. The aim of this study is to describe several aspects of the seasonal life cycle of Z. albicoxa, particularly the overwintering stage, reproductive period and voltinism.
This study was conducted on the campus of Hirosaki University, at Hirosaki, Aomori Prefecture (40°36′N, 140°29′E). To examine the seasonal occurrence of eggs and larvae of Z. albicoxa, nymphs and adults of the host spider, A. tepidariorum, were collected monthly during the period from May 1983 to December 1984. In the study area, both the nymphs and adults of A. tepidariorum occur throughout the year (Tanaka 1989). The collected spiders were brought to the laboratory, and eggs or larvae of Z. albicoxa on their abdomen were recorded. The parasitized spiders examined were returned to the collecting spots.
Adult wasps visiting spiders' webs and newly formed pupal cocoons on webs were counted weekly from April to October in 1987 at two sites on the campus: the northern and eastern sides of a block fence facing a street, where the density of the host spider was high. This census was carried out on fine days from 12.00 to 14.00 h.
To confirm the overwintering stage of this parasitoid, spiders just after hibernation were collected at several sites in Hirosaki City in March, 1985 and 1986, and eggs and larvae of the ectoparasitoid on their backs, pupal cocoons and adults on their webs were counted.
Eggs and larvae of Z. albicoxa were obtained from nymphs of various instars and adults of A. tepidariorum (Table 1). Without exception, only one parasitoid egg or larva was found on the abdomen of each host spider. The parasitoid larvae were found all the year round, but eggs were found only during the period from May to October. The earliest record of newly deposited eggs on the backs of spiders was 28 May in 1983 and 26 May 1984. No eggs were ever found on spiders collected in March, 1985 and 1986. Of 440 spiders collected, 34 were infested by the parasitoid larvae, but none was infested by the eggs.
Month | No. spiders | No. eggs (%) | No. larvae (%) |
---|---|---|---|
January | 52 | 0 (0.0) | 6 (11.5) |
February | 50 | 0 (0.0) | 4 (8.0) |
March | 79 | 0 (0.0) | 2 (2.5) |
April | 93 | 0 (0.0) | 2 (2.2) |
May | 156 | 8 (5.1) | 5 (3.2) |
June | 184 | 1 (0.5) | 6 (3.3) |
July | 179 | 2 (1.1) | 1 (0.6) |
August | 182 | 2 (1.1) | 4 (2.2) |
September | 196 | 1 (0.5) | 3 (1.5) |
October | 193 | 1 (0.5) | 5 (2.6) |
November | 177 | 0 (0.0) | 8 (4.5) |
December | 131 | 0 (0.0) | 14 (10.7) |
- The host spiders were collected every month from May 1983 to December 1984 on the campus of Hirosaki University.
Cocoons were not found in April and started to occur in early May. Many of them were produced in early May, mid-June and late July (Fig. 1). Adults were not found in April. They began to appear in mid-May, about a week later than pupae, and then they were observed visiting spiders' webs until late September (Fig. 1). In March, 1985 and 1986, I observed 440 spiders' webs at several sites in Hirosaki City, but neither parasitoid cocoons nor adults were found.

Seasonal occurrence of adult and newly formed pupal cocoon of Zatypota albicoxa on the campus of Hirosaki University in 1987. (●) Cocoons and (○) adults. In each census, more than 100 spiders' webs were observed.
The present results demonstrate that, at Hirosaki, the larva of Z. albicoxa occurs all the year round, while the egg, pupa and adult are restricted to occur only in the period from May to September or October (Table 1 and Fig. 1). Therefore, this parasitoid probably overwinters only in the larval stage. Similarly, post-overwintering nymphs of Theridion lunatum (=Achaearanea lunata) are infested by the larvae of Polysphincta eximia (=Zatypota albicoxa) in Denmark (Nielsen 1923).
In the Hirosaki population, all developmental stages from the egg to the adult of Z. albicoxa occurred in May, while only the larval stage was found in April (Table 1 and Fig. 1). This suggests that the larvae grew rapidly, became adults in May and started to reproduce shortly after emergence. The pupae began to occur in early May, adults in mid-May and eggs in late May (Table 1 and Fig. 1).
Under natural conditions, all developmental stages occur from May to September (Table 1 and Fig. 1). The parasitoid thus continues to grow and reproduce under warm conditions and adequate food supply. Because it completes its development from the egg to adult within 30 days at 24°C and the adult does not live more than 1 month in the laboratory (unpubl. obs., 2003), it seems that Z. albicoxa has a multivoltine life cycle. This inference is supported by the seasonal occurrence of newly formed cocoons. There were at least three peaks of abundance of cocoons (Fig. 1). The first peak in early May was derived from overwintered larvae and the second one in mid-June from those of the first generation. Although the number of newly formed cocoons generally decreased thereafter, the small peaks observed from late July to September seem to represent the second and the partial third generations, respectively.
ACKNOWLEDGMENTS
I thank the late Professor Setsuya Momoi for identification of the parasitoid and to Sinzo Masaki for the critical reading of an early version of the manuscript. Thanks are also due to Kazuhiko Konishi and Hajime Yoshida for providing information on Polysphincta eximia and Theridion lunatum, respectively.