BIONOMICS AND THE SIGNIFICANCE OF GLYPTAPANTELES LIPARIDIS (HYM., BRACONIDAE) AS A REGULATOR OF LYMANTRIA-DISPAR (LEP., LYMANTRIIDAE) IN DIFFERENT HOST POPULATION-DENSITIES

At three localities with initially high, intermediate, and low density populations of gypsy moth, stage specific parasitism by the gregariou s braconid, G. liparidis, was studied throughout the years 1993 to 199 5. Emergence of the parasitoid larvae from the collected gypsy moth la rvae started in the laboratory at 20 degrees C in the 19th and 20th we ek, that was two weeks earlier than in the held. Parasitoid larvae mai nly emerged from 4th instar hosts 1993. Delayed development of gypsy m oth larvae in field, caused by low temperatures during spring in the y ears 1994 and 1995 and partly by artificial augmenting at the innocuou s site, increased parasitization rate by the braconid wasp in total an d the number of 3rd instar hosts from which parasitoids emerged. A bim odal mode of emergence was found in 1994 when parasitoid larvae left t heir 3rd or 4th instar hosts between the 19th and 23rd week and the 4t h, 5th, and one 6th instar hosts between the 25th to 28th week. Genera lly, more parasitoids emerged from 4th instar hosts than from older ho st instars. Highest parasitism at a rate of 48% was found in gypsy mot h larvae of the 3rd and 4th stadium at the low density site, where the gypsy moth population was artificially augmented. Overall, we found i ndications of an inverse relationship between host density, estimated by the number of egg masses, and the rate of parasitism by G. liparidi s, but a density dependent relationship between egg masses and the num ber of cocoon clusters of the parasitoids in low and intermediate gyps y moth populations. Thus, the parasitized species is believed to be a specialist of low host population densities. The rate of parasitized h ost larvae, however, was not correlated with the number of cocoon clus ters of the emerged parasitoid larvae counted in autumn. Hyperparasiti sm of the parasitoid cocoons was between 6 and 15% during outbreak con ditions of gypsy moth.