The natural enemy complex of the gypsy moth, Lymantria dispar (Lep., Lymantriidae) in different phases of its population dynamics in eastern Austria and Slovakia - a comparative study

Parasitism and pathogen mortality of Lymantria dispar were compared between host populations of different densities in Slovakia and Austria. Over a pe riod of 4 years, L. dispar eggs, larvae, and pupae were collected in a stag e-specific manner at three mixed oak stands in each country and reared in t he laboratory to assess parasitoid and pathogen mortality. At sites with lo w host densities, L. dispar abundance was artificially augmented by exposin g egg masses and young larvae. We ascertained marked differences between th e natural enemy complexes of L. dispar populations in Slovakia and Austria. Overall, pathogens caused highest mortality in the former and parasitoids in the latter. Moreover, the species composition differed significantly bet ween on both countries. High variation was also observed between years and host populations at different densities. The investigations revealed that e gg parasitization was low in Slovak L. dispar populations, and no egg paras itoids were found in Austria. Larval and pupal parasitism was low at sites with outbreak populations, but higher at the Austrian than at the Slovak si te. The tachinid Parasetigena silvestris was the dominant species at elevat ed host densities. Nuclear polyhedrosis virus also caused significant morta lity in these cases. An increase in parasitism by several species was notic ed after the breakdown of L. dispar populations. The ichneumonid Phobocampe spp. caused high levels of parasitism during the post-culmination years. A t sites where host abundance increased in the first year of the study, sign ificant differences bt tu ccn the Austrian and the Slovak locality could be ascertained. Mortality was ion: in the population at the latter site, and host abundance increased to outbreak levels the year after. The population at the Austrian site suffered high parasitism by the tachinids P. silvestri s and Blepharipa pratensis and this might have contributed to the preventio n of a further increase in L. dispar abundance in this locality. Braconids showed a strong reaction to the local, artificial increase in host density at study plots with innocuous L. dispar populations. Particularly high para sitism by Glyptapanteles liparidis was observed at the Austrian site, but G . porthetriae and Cotesia melanoscela also accounted for significant mortal ity in both low-density populations. The artificial L. dispar populations w ere usually eradicated by natural enemies before pupation of the hosts.