ANNUAL REPORT OF THE SOCIETY OF PLANT PROTECTION OF NORTH JAPAN

Adult European tarnished plant bugs, Lygus rugulipennis Poppius, were dipped in insecticides. The mortality rates of bugs 24 hours after dipping in insecticides diluted with 16000 parts of water were 100% in fenthion (with 50% active ingredient), 87% in ethofenprox (20%), 80% in cyanophos (50%), 67% in phenthoate (50%) and fenitrothion (40%), 60% in permethrin (20%), 42% in imidacloprid (10%), 27% in fluvalinate (20%) and cypermethrin (6%), and 0 % in acephate (50%).

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Adzuki bean plants, Vigna angularis, were sprayed with seven insecticides in Kunneppu, Hokkaido to control seed injury caused by the European tarnished plant bug, Lygus rugulipennis Poppius. The effect on reduction of seed injury was higher in the case of treatment with fenthion, followed by phenthoate, cyanophos, fenitrothion, cypermethrin, and ethofenprox. No such effect was observed on seeds from plants sprayed with pymetrozine, an antifeedant. This agrees better with the result from the release experiment on plants treated with insecticides than the result from the bug dipping experiment

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The effect of four insecticides, which is resistered for use on cabbage in Japan, on Diadegma semiclausum, a larval parasitoid of the diamondback moth, Plutella xylostella, was assessed by four different bioassays, i.e., (1) dry film assay, (2) semifield assay in the cage, (3) direct spray assay for parasitoid cocoons, and (4) parasitizing assay using females that survived the dry film assay. The results showed that chlorfluazuron (IGR) and the microbial toxin from Bacillus thuringiensis var. kurstaki had minimun effects on D. semiclausum in all the assays. Ethofenprox (pyrethroid) showed the highest insecticidal activity in the dry film assay (100%, female mortality), however moderate mortality was observed in the semifield assay (32%) and in the direct spray assay (76% of cocoons could have emerged). Pyrazole chlorfenapyr showed moderate toxicity to D. semiclausum in all the assays. These results suggest that an inappropriate assay could lead to an erroneous conclusion on the actual effect of an insecticide on natural enemies, such as D. semiclausum, which exhibits high locomotive ability and some repellency to insecticides under field conditions.

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The Japanese population of the black vine weevil, Otiorhynchus sulcatus (Fabricius), were found to exhibit an aggregation behavior, like as the European population. Females tended to aggregate, particularly when diets were removed. Observation using the Y-tube olfactometer revealed that females were attracted to other individuals, but not to body extracts by hexane.

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