島根県におけるウンカ・ヨコバイ類天敵の寄生率の季節的変動

Seasonal change in leaf- and planthoppers parasitized by dryinid wasps, stylops, mermitid worms and pipunculids was investigated at paddy fields and the ridges between them in Shimane pref. in Japan from 1978 to 1984. Twelve species of nymphal parasitoids, viz. 6 species of Dryinidae, 1 species of Elenchidae, 1 species of Mermitidae and 4 species of Pipunculidae, were collected at these places. These nymphal parasitoids showed host specificity, which was extended to the family level in the pipunculid, stylop and mermitid worm species. Namely, Haplogonatopus atratus parasitized Laodelphax striatellus ; H. japonicus and Echthrodelphax bicolor parasitized Sogatella furcifera ; Pseudogonatopus fulgori parasitized L. striatellus and S. furcifera ; P. flavifemur parasitized Nilaparvata lugens ; and Tetradontochelys sakaii parasitized Nephotettix cincticeps. In other field studies E. bicolor has been found to parasitize L. striatellus and N. lugens. L. striatellus, S. furcifera and N. lugens was parasitized by Elenchus japonicus and Agamermis unka as well as Dryinid wasps, and N. cincticeps was parasitized by pipunculid species. The percentage of parasitism of L. striatellus by dryinid wasps increased considerably at the beginning of crop period in June and at the time of high population of hosts in paddy in August and September, but it was generally in low level under 10 %.Parasitism of S. furcefera by dryinid wasps was generally at about 10 % though it occasionally could reach more than 20 % in June and July. There are no obvious correlations between host population and parasitism by dryinid wasps. The percentage of parasitism of N. lugens and N. cincticeps by dryinid wasps was under 1-2 %. E. japonicus was found to infect delphacids from July. The percentage of parasitism ranged from 0.1 to 26.7 % and was generally high in August. S. furcifera parasitized by E. japonicus was predominant comparing with L. striatellus and N. lugens parasitized by it. A. unka was found to infect delphacids from August to September and the parasitism by it was occasionally at about 20 % in L. striatellus and S. furctfera and at more than 30 % in N. lugens at a paddy in lzumo. Pipunculids were found to infect N. cincticeps from August to October and the percentage of parasitism by them generally ranged from 3 to 5 %. The parasitism by the nymphal parasrtoids remained relatively stable when the insecticide was spryed, although there was a decrease in the population of hosts. A number of non-parasitized and parasitized hosts migrated to the ridge between rice fields overgrown with weeds when insecticide was sprayed on the rice plant at paddy fields. S. furcifera multiparasitized by dryinid wasps and E. japonicus was collected from the middle of July to the middle of September and the highest percentage of multiparasitism was 7% in both the parasitoids. S. furcifera parasitized simultaneously by dryinid wasps and E. japonicus was collected from the middle of July to the early of October and the highest percentage of gregarious parasitism reached 23.2% in a case.