DIFFERENT PARASITISM PATTERNS OF 2 HYMENOPTEROUS PARASITOIDS (ICHINEUMONIDAE AND IBALIIDAE) DEPENDING ON THE DEVELOPMENT OF SIREX-NITOBEI (HYM, SIRICIDAE)

For the two parasitoid wasps, Ibalia leucospoides and Megarhyssa praec ellens emerging together with their host woodwasp, Sirex nitobei, from trees of Pinus densiflora, the seasonal trends in number of emerging adults, their body size characteristics and fecundities were recorded to evaluate the life histories and parasitism patterns. The mean femal e body mass of M. praecellens was about 1.8 times (fall population) or about 4.1 times (spring population) larger than that of I. leucospoid es. The difference in body size was remarkable also between sexes in b oth species. The spring population of M. praecellens was about 3.7 tim es (male) or 2.3 times (female) larger in mean body weight than the fa ll population. The mean egg length of M. praecellens was about 10 time s larger than that of I. leucocpoides, whereas I. leucospoides produce d about 50 times greater numbers of eggs than M. praecellens. The perc entage of parasitism on S. nitobei by both parasitoids was considerabl y large, accounting for more than 60%. Our results suggested that two parasitoid species could utilize larvae of S. nitobei in wood as their hosts at different development stages of woodwasp in different manner s: egg and/or Ist instar larvae parasitized by I. leucospoides and mat urated larvae by M. praecellens.