Mycetophagous females, males and infective females of the genus Iotonchium which had not been known in Japan were found from gill-galled oyster mushrooms, Pleurotus ostreatus, which were collected at some localities of Tottori Prefecture in the late autumn of 1992 and 1993. By comparison with seven previously described species of Iotonchium, this nematode was named I. ungulatum n. sp. (“hiratake-hidakobu-senchu” in Japanese) and described here. The new species is apparently distinguished from I. bifurcatum, I. californicum, I. cephalostricum, I. fungorum, I. imperfectum and I. macrospiculatum by having peculiar L-shaped spicules with a paw-like tip in the male (specific name is derived from this characteristic). From I. mycophilum whose male has not been known, the new species is differentiated by the shorter body length and the pointed tail terminus in the infective female.

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Meiosis after fertilization was examined in temperature-sensitive embryonic arrest mutants, emb-1 (hc 57) and emb-3 (hc 59). In emb-1 embryos, normal meiosis-I spindles were formed; however, spindles and chromosomes were subsequently deformed and no polar body was produced. In emb-3, meiosis-I spindles were disorganized, positioning of chromosomes was abnormal and all chromosomes were often extruded as a single large polar body. These results suggest that emb-3 but not emb-1 is required for meiosis-I spindle formation and that emb-1 but not emb-3 is required for polar body formation.

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In this study, the efficacy of two entomopathogenic nematodes species against the potato weevil, Cylas formicarius, a serious pest of sweet potato in Sri Lanka was evaluated. In the laboratory, Heterorhabditis megidis produced 80-90% mortality of larvae, pupae and adults while Steinernema feltiae produced 70-80% mortality. In a small plot experiment under field conditions also showed significant insecticidal efficacy on the weevil thereby reducing damage to local sweet potato varieties, CARI-426, CARI-426-13. Although carbofuran gave a considable reduction in damage by the weevil, the degree of control was significantly less than those of two nematode species. A field experiment conducted in large pots with thevariety, Wariyapola Red, showed low levels of weevil control due to S. feltiae or carbofuran. However, H. megidis produced significantly higher levels of weevil control than S. feltiae or the chemical. Results of the experiments on potential of two entomopathogenic nematode species showed a possibility of biological control measure against sweet potato weevil in Sri Lanka.

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Development of endotokia matricida and emergence of originating infective juveniles from maternal cadavers were comparatively investigated in vivo and in vitro for Heterorhabditis bacteriophora, Steinernema glaseri, and S. carpocapsae. In the host insect Galleria mellonella larvae, endotokia matricida develop more fast and frequently in the 1st to 3rd generation females of the heterorhabditid than of the two steinernematids. The ratio of females bearing endotokia matricida increased with the increase of the inoculum size from 25 to 1, 600 per host insect. The infective juveniles produced via endotokia matricida emerged mainly from natural openings of the maternal cadavers for the two steinernematid nematodes, while those of the heterorhabditid did mainly transcuticularly. Under in vitro conditions, induction rate of endotokia matricida was higher in RINGER'S solution than on nutrient agar amended with or without the symbiotic bacteria of respective nematode species.

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To determine host suitability of sweet potato to major Meloidogyne species, penetration of second stage juveniles (J2) and their early development, and production of egg-masses were examined. Cuttings of four sweet potato cultivars, Norin No.1, Norin No.2, Kokei No.14 and Beniazuma, rooted in 200g of sterilized potted soil were inoculated with approximately 500 newly hatched J2 and grown in a green house at an average temperature of 27°C. Five days after inoculation penetration and development of J2 were examined, and after 35 days numbers of egg-masses on root systems were counted. Numbers of egg-masses produced by M. incognita markedly varied according to cultivars. M. arenaria laid some eggmasses on cultivars except Norin No.1 on which no egg-mass was observed. A few eggmasses were produced by M. hapla on all four cultivars, but none by M. javanica. J2 of M. arenaria, M. incognita and M. javanica penetrated roots of all cultivars well and more than 50% of penetrated J2 enlarged as early as five days after inoculation on cultivars with eggmasses, though only a few J2 enlarged on those cultivars with no egg-masses. J2 of M. hapla penetrated roots of all 4 cultivars but only a few J2 penetrated and developed.

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[in Japanese]

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