Prokelisia marginate (Homoptera:Delphacidae) is the most common homopteran in- habiting salt marsh cord grass, Spartina alterniflora, in northwest Florida. Eggs are inserted into host leaves. Egg parasitism by Anagrus delicatus (Hymenoptera: Mymaridae) was inversely density de- pendent within leaves, among leaves and among sites. No density dependence was found on any scale. Temporal changes in egg density and parasitism through the year on one islet conformed to the general pattern of inverse density dependence. The graphed time sequence of parasitism rate did not cycle in an anticlockwise direction; thus the data indicate no delayed density dependence. Ab- normally high egg densities in experimental cages of Prokelisia populations did not cause a corre- sponding increase in egg parasitism. Parasitism in both experimental and adjacent control populations was inversely density dependent. Although individual parasitoids may search aggregatively and kill hosts in a density-dependent fashion in some laboratory experiments, many factors in nature can change the relationship at the population level. We propose that periodic tidal inundation of S. alterniflora may disrupt parasitoid searching and affect parasitism rates as a function of density.