Temporal and spatial variation in a parasitoid community associated with the herbivores that feed on Missouri Quercus

To determine whether the probability of parasitoid attack differed across years, seasons, sites, host plant species, and herbivore feeding modes, leaf-chewing insects (Lepidoptera) that feed on Quercus alba L. and Q. velutina Lam. were collected four times in the Missouri Ozarks (May, June, July, and August-September) in each of the years 1993-1995 and reared in the laboratory. Parasitism rates at a given census were relatively constant from year to year and decreased as the season progressed from May to September: 30% of the herbivores collected in May were parasitized, whereas <15% were attacked in the summer and fall. Similarly, parasitism rates were predictable based on host plant (higher on Q. velutina than on Q. alba) and feeding guild (higher for leaf miners than for external feeders, leaf tiers and leaf webbers, in the summer and fall). Leaf rollers encountered in May had the highest probability of being parasitized. There was also significant variation in parasitism rates among sites. Community composition during the spring was very similar among spring censuses across years and different from all other censuses. In contrast, in the summer and fall, the species assemblage of the parasitoid community remained relatively constant within a year despite the fact that the herbivore community composition changed across censuses.