The distribution of Pratylenchus spp. in tobacco fields in eastern Japan, excluding Hokkaido, was surveyed. Pratylenchus spp. from soil samples of 151 tobacco fields were identified by PCR-RFLP analysis. The PCR products of the two internal transcribed spacer regions, the 5.8S gene, and small portions of the 18S and 28S genes of the ribosomal DNA on individual root-lesion nematodes were digested with AluI and HinfI, and about 10 nematodes per field were individually identified using the two species-specific RFLP patterns. In this work, five Pratylenchus spp.: P. penetrans, P. crenatus, P. neglectus, P. zeae and P. sp. near coffeae were found, but no P. coffeae was detected. Pratylenchus penetrans, and P. sp. near coffeae were distributed most widely, with detection rates of 53.0%, and 49.7%, respectively. Pratylenchus crenatus, and P. neglectus were distributed sporadically, with detection rates of 2.6%, and 2.0%, respectively. Pratylenchus zeae was found only in one field in Tochigi Prefecture.

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The seasonal occurrence of Liriomyza trifolii adults in gerbera greenhouses was monitored with yellow sticky traps. Dead L. trifolii larvae collected from gerbera leaves were dissected to determine their mortality factors. The mortality, rate of parasitism, and survivorship were estimated using the observed numbers of dead, parasitized, and living L. trifolii larvae. Six eulophid species were found in the greenhouses as larval parasitoids of L. trifolii. Neochrysocharis formosa and Chrysocharis pentheus were dominant, followed by Diglyphus albiscapus. Routine surveys revealed low parasitism (0%-1.3%) in conventional greenhouses where non-selective insecticides were applied frequently. After insecticide applications were stopped in these greenhouses, the L. trifolii population increased, followed by an increase in the rate of parasitism by indigenous parasitoids. Moreover, the larval mortality of L. trifolii also increased, presumably due to host-feeding by eulophid adults. These results indicate that eulophid parasitoids play an important role in suppressing L. trifolii population.

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The response of the egg parasitoid wasp, Ooencyrtus nezarae Ishii to eggs of the two host bugs, Riptortus clavatus and Piezodorus hybneri, was investigated in laboratory experiments. In a test tube, 80% to 100% of O. nezarae female wasps parasitized eggs of R. clavatus. On the other hand, less than 60% of females parasitized egg masses of P. hybneri. The female wasps tended to attack R. clavatus first when provided with eggs of both R. clavatus and P. hybneri in a test tube, and took more time to start oviposition behavior on P. hybneri eggs than on R. clavatus eggs. These results indicate that O. nezarae females prefer R. clavatus eggs to P. hybneri eggs. The females' acceptance ratio for R. clavatus did not change after several generations reared on P. hybneri, suggesting that the preference for R. clavatus is partly determined genetically. Significantly higher survivorship was recorded in O. nezarae developed in eggs of R. clavatus than in eggs of P. hybneri. In addition, female wasps emerging from R. clavatus showed greater fecundity and longevity. These findings suggest that the preference for R. clavatus is correlated with the reproductive success of O. nezarae on R. clavatus.

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The acaricide milbemectin causes high mortality of newly hatched larvae of the agromyzid leafminer, Liriomyza trifolii (Burgess) on kidney bean plants. A similar effect is observed with use of emamectin, which, like milbemectin, is derived from chemicals produced by soil bacteria. Most of the 1- and 2-day-old leafminer larvae died after application of milbemectin at 20ppm. Even at 7.5ppm, significantly fewer larvae grew to pupa compared to controls. Use of milbemectin did not have any adverse effect on development of the parasitoid Diglyphus isaea (Walker) during the larval and pupal stages nor on the survival rate of the emerged adult wasps. These results indicate that milbemectin can be integrated into IPM programs to control both L. trifolii and mites.

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A high rate of abnormally stained fruit was produced by introducing the two-spotted spider mite, Tetranychus urticae Koch, into bagged fruit of the Japanese pear cv. Nijisseiki, especially during July and August. Many punctures made by the spider mites were observed on the stained lesions using SEM. This is a new type of damage called “usuzumi” (gray stain), caused by the two-spotted spider mite.

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Egg parasitoids of the bean bug, Riptortus linearis were investigated in a soybean field on Okinawa Island in October 1996. Only one species of egg parasitoid emerged from R. linearis eggs collected in the soybean field and it was identified as the wasp Gryon nigricorne. The wasps also emerged from host eggs placed artificially in the soybean field. In both cases, no other egg parasitoid species was recorded.

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