Biological Investigations on Some species of Anagrus (Hymenoptera, Mymaridae), Egg Parasitoids of Leafhoppers (Hemiptera)

摘要

Biological investigations were carried out on entomophagous parasitoids of leafhopper eggs associated with Juncus in South Wales, U.K.. The hosts and parasitoids were reared in cages in greenhouse at the temperature of 22 C. The life cycle and seasonal changes of Anagrus were examined in the laboratory and in the field. Process of emergence, movement, searching for host eggs, copulation, and oviposition were also observed. Five species of Anagrus were found parasitizing leafhopper eggs. The ratio of males to females was found about one to one. The possibility of infestation depends highly on host eggs laid in living plant tissues. A female contains about 46 ovarial eggs but only 50% are laid in host eggs. In laboratory condition (+22 C) the period of development is about 15 to 20 days for one generation but in natural condition in May and June the first two generations require about 25 to 55 days each. The adult parasitoids disappear at the beginning of cold weather which starts by the middle of October to middle of November. Their development stages spend the winter in the host eggs. The Mymarids produce a high infestation rate of host eggs (often 50 to 70%). Some of their hosts such as Cicadella viridis (L.) (Cicadellidae) and Conomelus anceps Germar (Delphacidae) are important pests. Five closely related species found during investigation attacking leafhopper eggs in Juncus stems are Anagrus ensifer Debauche, A. breviphragma Sokya, , A. incarnatus Haliday, Anagrus sp. A and Anagrus sp. B. This preliminary nomenclature is used because the taxonomy of this group is complex and species identification is difficult. Anagrus species emerged during investigations were found to be highly specific. Each species was restricted to the eggs of one host species in Juncus. Anagrus ensifer Debauche and A. breviphragma Sokya were found to be gregarious, the remaining species as solitarious. Egg parasitoids have the advantage that they attack the early life history stages of the pests before damage can be done. The relatively high rate of reproduction, and the short period of development are the main reasons for the great efficiency of these parasites.