Rhugnletis conversa (Bréthes) is a Chilean species of Tephrilid fly which attacks fruils of native Solanumtomatillo and Solanum mgnim. This species show two host races. An ecological and reproducliveresearch un natural populations of these two races is the subject of this paper. The results prove thatboth races offer seasonal differenliation in their populalion distribulion, mating behaviour andoviposition.