Gas chromatography analysis of Lutzomyia longipalpis (Lutz & Neiva) pupae and fourth instar larvae revealed a compound which was not present in other larval stages. Squashed pupae were repellent to conspecific larvae and ants (Lasius niger (Linnaeus) (Hymenoptera: Formicidae)), whereas second and third instars were not. Hexane extracts of pupae were repellent to conspecific larvae and L. niger, but extracts of second and third instars were not. The biologically active chemical was isolated from pupae and fourth instars and was found to be repellent to conspecific larvae and L. niger. The possibility that pupae and fourth instars may use a combined chemical and mechanical defensive strategy to avoid predation and cannibalism is discussed.