Studies on the Egg Parasites of the Smaller Brown Planthopper, Laodelphax striatellus (FALLEN) : Hemiptera : Delphacidae : IV. Seasonal Trends in Parasitic and Dispersal Activities, with Special Reference to Anagrus nr. flaveolus WATERHOUSE (Hymenoptera : Mymaridae)

Abstract

Parasitic activity of wasps attacking delphacid eggs on cultivated plots and the intensity of their dispersal were studied by setting in the outdoors flower-pots bearing Laodelphax striatellus eggs. Anagrus nr. flaveolus was an overwhelmingly dominant species. The parasitic activity of the species was ascertained on wheat late in April. It was also clarified that the parasite had already existed on the early-season transplanted rice crops when the adults of L. striatellus were about to invade. An increase of parasitic activity in autumn was demonstrated on paddy plots. Dispersal of Anagrus to a bare ground on which the research was carried out tended to be continuous all through the season. In autumn, the intensity of dispersal was heightened remarkably. Adaptive significance of the autumn dispersal is discussed in relation to possible ways of hibernation of the parasite. A different species of Anagrus and a trichogrammatid belonging to genus Oligosita were also recorded occasionally in autumn. The species, however, were mainly obtained on the bare ground and are guessed to be mere facultative inhabitants on rice crops.