Proceedings: ecology, survey and management of forest insects

Predation of gypsy moth egg masses was studied in Slovakia from 1999 –2002. Predation on naturally laid egg masses was recorded and linear regression was used to test the hypothesis that predation follows a type II vs. type III functional response. We also investigated the role of egg mass predation in gypsy moth population dynamics. The relative contribution of invertebrates vs. vertebrates as agents of predation on egg masses was estimated using exclosures. During the study, population densities remained very low and stable. Generally, invertebrata caused 38% and vertebrata 62% of total predation. K-values varied from 0.03 to 0.70 and plots of abundance vs. k-values suggested that total predation is inversely density dependent, characteristic of a “type II” functional response. The ultimate role of predation on gypsy moth egg masses remains unclear, however there are some indications that egg mass predation plays a significant role in the dynamics of gypsy moth populations in Slovakia. Introduction The gypsy moth (Lymantria dispar) is the most serious pest of broadleaved stands (oak stands mainly) in Slovakia. Outbreaks are repeated in cycles of 6 to 12 years. During the last outbreak of 1992 1994, gypsy moth severely damaged more than 18,000 ha of forest land. In stands exhibiting patterns of long-term oak decline, defoliation can cause increased tree mortality in subsequent years and therefore, infested stands are often treated with biopesticides, mainly Bacillus thuringiensis. The key biotic factors influencing population dynamics during the latency phase are not well known in Slovakia. Conversely, the bioregulation complex of gypsy moth is better understood in the U.S.A. (Doane and McManus 1981, Elkinton, Liebhold 1990). The goal of this paper is to present results on a study of gypsy moth egg mass predation during the latency phase. The objectives of this study were to: Determine the relationship between predation and gypsy moth densities (i.g. identify the type of functional response); evaluate the role of egg mass predation in gypsy moth population dynamics; and quantify the relative levels of predation caused by vertebrates vs. invertebrates. Material and Methods Survey of Population Density A series of 12 study plots was established across the outbreak area of gypsy moth in southern Slovakia (Fig. 1). Surveys of population density were conducted using the Modified Turcek method (MTM) (Turcani 1998). MTM consists of counting the number of egg masses on 4 points (every point consists of 30 trees) in the study area. If the average number was over 1.00 egg mass per tree, the survey was terminated. If it was below 1.00 egg mass per tree, counting continued on another 4 points (together 240 trees). If the population density was below 0.3 egg masses, another 8 points were taken. The total arrangement consisted of 480 trees. Egg masses were found on trunks from ground level to the 5 – 8 m.