Pathogenicity of indigenous steinernematids against some noctuid larvae was examined to screen candidates in a biological control program. First, 17 isolates from ten species (Steinernema feltiae, S. kraussei, S. kushidai, S. litorale, S. monticolum and five RFLP types) were screened for pathogenicity against the middle instar larvae of Peridoroma saucia, and S. feltiae and S. litorale were selected. Secondly, three isolates of S. feltiae and eight isolates of S. litorale were screened for pathogenicity against the middle instar larvae of Agrotis segetum, and S. feltiae HkEr36 and S. litorale IbKt142 were selected. Both isolates showed high pathogenicity at 25°C and below, but reduced pathogenicity at 30°C. Therefore, with the addition of a subtropical species S. abbasi collected after the second screening, the screened isolates were compared with an introduced nematode, S. carpocapsae All, for their pathogenicity against the late instar larvae of A. segetum and Spodoptera litura. The isolate S. litorale IbKt142 showed high pathogenicity between 7 and 25°C, and caused significantly higher mortality of A. segetum at 7, 10 and 15°C and S. litura at 7 and 10°C than S. carpocapsae All did. Moreover, S. abbasi OnIr181 caused significantly higher mortality of A. segetum at 30 and 35°C and S. litura at 35°C than S. carpocapsae All did.

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A direct quantification method consisting of soil compaction and real-time PCR was applied to quantify the potato cyst nematode (PCN), Globodera rostochiensis, in soil. We also compared the efficacies of pre-treatment methods for disrupting nematode bodies and obtaining homogeneous soil samples between soil compaction and ball milling. PCN was detected at a density of five second-stage juveniles (J2)/20 g of soil and there were highly significant correlations (r² > 0.8697) between the cycle threshold (Ct) values and the number of J2 inoculated in all the soils, irrespective of the pre-treatment methods. Calibration curves showing the relationship between Ct values and nematode density were almost identical for both pre-treatment methods in two soils, while the Ct values were consistently lower for the ball milling method in one soil, suggesting that DNA extraction efficiency might be better in the ball milling method. The calibration curves obtained with the ball milling method were nearly identical in three soils, but were different with the compaction method. These results suggest that the ball milling method is more suitable for direct quantification of nematodes than the compaction method.

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Caenorhabditis japonica forms an intimate association with the shield bug Parastrachia japonensis. Quiescent dauer larvae (DL) are always found on female shield bugs aggregating on leaves in reproductive diapause throughout the year until the next reproductive period in June, which suggests long-term survival of DL on the shield bugs without propagation. To understand the morphological significance of DL on the shield bug, cryo-scanning electron microscopy (Cryo-SEM) was performed. Cryo-SEM observation revealed that the DL appeared to be partly desiccated, but their lateral alae were not shrunken as seen in the anhydrobiotic nematode Aphelenchoides besseyi. To test DL survivorship on the shield bug, we collected bugs from the field and kept them under several experimental conditions for 3 months. When bugs were kept at 100% relative humidity (RH), very few nematodes were detected. When bugs were exposed to 97% RH using a K₂SO₄-saturated solution, a small number of nematodes (19 DL/bug) was detected and DL survival was low (33%). At 90% RH in a wooden box, more nematodes (67 DL/bug) were detected and survival was high (54%). These data suggest that DL are able to survive several months on shield bugs by entering a partially desiccated quiescent form.

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[in Japanese]

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Abstracts of papers presented at the 18th annual meeting of the Japanese Nematological Society in Sapporo, August 26-28, 2010

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