No abstract

Experiments were conducted to elucidate the reproductive strategy of the siricid woodwasp, Xeris spectrum, which carries no substantial symbiotic fungi in its body, in a comparison with the life cycles of two fungus-carrying siricid woodwasp species, Sirex nitobei and Urocerus japonicus, by considering ecological traits such as seasonal patterns of occurrence, spatial distribution of emergence on a tree, and oviposition activities. Part of the X. spectrum populations emerged in spring, during May and June, while others emerged in summer, during August and September, simultaneously with other siricid fungus-carrying woodwasps. The vertical distribution pattern of X. spectrum emergence holes on the trunk closely coincided with the emergence hole pattern of S. nitobei. X. spectrum laid few eggs on fresh logs, old logs, or on logs inoculated with potato dextrose agar, whereas on logs inoculated with Amylostereum chailletii or A. areolatum, X. spectrum females oviposited no less than 30%, on average, of their potential eggs. Moreover, the oviposition sites on these logs were concentrated near the Amylostereum inoculation positions. These results indicate that X. spectrum has evolved a life history that utilizes fungal symbionts of other woodwasp species without itself possessing any symbiotic fungus. Moreover, X. spectrum has evolved a dual reproductive system in that (1) some adults emerge in summer during the same emergence period as the fungus-carrying woodwasps and thereby oviposit on host trees already inoculated with fungi, and (2) other adults emerge the next spring and oviposit on trees that were inoculated with fungi a year earlier.

The causative agent of Q fever, a widespread zoonotic disease, is the bacteria Coxiella burnetii. Although cases of Q fever have been documented in countries throughout the world, the prevalence of the disease in Japan is not yet known. Q fever is a demonstrated occupational hazard to those employed in zoological professions, but the risk to Japanese veterinarians has not yet been quantified. In order to evaluate the risk to Japanese veterinarians, we performed a serological survey using serum samples from 267 veterinarians. Two control groups consisting of 352 medical workers and 2003 healthy blood donors were also evaluated. The antibody titers of the serum samples were measured by indirect immunofluorescence assay (IFA) using phase II C. burnetii Nine Mile strain as the antigen. The positive rate of IgG antibody was 13.5% in the veterinarians, which was higher than in the blood donors (3.6%, p < 0.001) and medical workers (5.1 %,p < 0.001). These findings suggest that Japanese veterinarians have a higher risk of infection by C. burnetii than other members of the Japanese population. An interesting finding of this study was that positive rates of IgG and IgM antibodies in the blood donor group were higher in younger individuals. The IgM antibody positive rate was the highest in females under 30 years old.

For the two parasitoid wasps, Ibalia leucospoides and Megarhyssa praecellens 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 female body mass of M. praecellens was about 1.8 times (fall population) or about 4.1 times (spring population) larger than that of I. leucospoides. The difference in body size was remarkable also between sexes in both species. The spring population of M. praecellens was about 3.7 times (male) or 2.3 times (female) larger in mean body weight than the fall population. The mean egg length of M. praecellens was about 10 times larger than that of I. leucocpoides, whereas I. leucospoides produced about 50 times greater numbers of eggs than M. praecellens. The percentage of parasitism on S. nitobei by both parasitoids was considerably 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 manners: egg and/or 1st instar larvae parasitized by I. leucospoides and maturated larvae by M. praecellens.

Experiments were conducted to elucidate how the oviposition activities of Sirex nitobei Matsumura could be affected by different conditions of the host trees, using logs from felled healthy trees and the dead and living trees of Pinus densiflora Sieb. et Zucc. According to days elapsed after tree-felling, the proportions of oviposition, defined as the proportion of eggs laid to the potential fecundity of a female during her lifetime, could be divided arbitrarily into three groups. The proportions of oviposition on the logs within 0-3 days after felling, i.e. fresh logs, varied greatly from log to log, and about half of female adults showed proportions of oviposition under 50% (mean +_ SD: 39 -----32%). However, all the females that oviposited on the logs 4-24 days after felling, i.e. intermediate logs, invariably showed proportions of oviposition over 50% (88 -----15%). On the other hand, proportions of oviposition in most of the females that oviposited on the logs over 25 days after felling, i.e. old logs, were less than 50% (26 _-+ 17%). The proportions of oviposition were significantly different between intermediate logs and old logs. The mean proportion of oviposition on living trees and that for dead trees were 45 and 58%, respectively. Thus, S. nitobei in the field would exhibit its preference for weakened trees of/'. densiflora as oviposition sites, as it did for the logs 4-24 days after felling in this study.