Investigations were undertaken in Jamaica to determine whether or not the application of malathion for the control of the West Indian cane-fly, Saccharo-sydne saccharivora (Westw.), disturbed the natural control exerted by Lixophaga diatraeae (Tns.) on its host Diatraea saccharalis (F.). It was demonstrated, by exposing caged adults of Lixophaga, that adults present in the field at the time of insecticidal application would be killed but because of the short residual action of malathion the reduction in the parasite population would only be temporary. A comparison of the degree of parasitism in sprayed and unsprayed fields did not reveal any evidence of reduction in the rate of parasitism. The extent of damage by Diatraea in sprayed fields was significantly less than in unsprayed ones and factors which might account for this are discussed.