The host-finding activity ofLeiophron pseudopallipesLoan centers on floweringErigeronplants. Several plant-related variables that could affect host-finding success were studied. These included plant height, plant density, host density per plant, the presence of unattractive plants in the habitat, and the background color ofLygus lineolaris(Palisot de Beauvois) feeding sites on the plants. Although the highest percentage ofLygusnymphs parasitized was associated with the same plant-height class in all fields sampled, plant height is probably unimportant in the host-finding behavior ofL. pselldopallipes. Plant height is influenced by plant density, and evidence suggests thatL. pselldopallipesis differentially attracted to areas of the habitat with the greatest density ofErigeronplants.Lygusdensities are also higher where theErigerondensities are greatest, which sometimes gives rise to a correlation between parasitization andLyglisdensity.The presence of other herbs inErigeronpatches appears to lower the attractiveness of these stands toL. pseudopallipes. It is suggested that these plants may disrupt the olfactory cues used in host finding. The contrasting background color of theErigeronplants also influenced parasitization. ReddishL. lineolarisnymphs, which tend to contrast with green plant background, were 3 times as apt to be parasitized as the green nymphs.