Technical Abstract: Sex pheromone-related behavior and chemistry were studied in the wasp Spalangia endius Walker (Hymenoptera: Pteromalidae), a pupal parasitoid of house flies Musca domestica L. (Diptera: Muscidae). Males responded behaviorally to female extracts by arrestment, whereas females did not arrest to male extracts. In a comparison of male and female extracts by GC/MS, two female-specific compounds were found. One was identified as methyl 6-methylsalicylate (gas chromatographic retention time and mass spectrum versus an authentic standard), but the chemical structure of the second compound is still unknown. Male antennae were sensitive to both compounds in electrophysiological tests (GC/EAD). Males responded behaviorally to methyl 6-methylsalicylate by arrestment, but they did not arrest to the second compound. The methyl 6-methylsalicylate has been previously reported from some ant and beetle species, but never from Pteromalidae. The analytical data and the male behavioral results are consistent with the idea that methyl 6-methylsalicylate functions as a female-emitted pheromone component at short range, but the exact role of both compounds in intersexual interactions in S. endius remains to be determined.