Actinomyces rhodnii has been isolated regularly from Rhodnius prolixus reared in the laboratory. It is not transmitted through the egg but is taken up by the young nymph from the environment; sometimes from the contaminated surface of the egg; more often perhaps from the dry excreta of other members of the species.Rhodnius has been reared free from Actinomyces by sterilizing the surface of the egg and feeding with suitable precautions.These sterile insects grow and moult normally until the 4th or 5th instar. Moulting is then delayed or may fail entirely in spite of repeated feeds of blood. Very few insects without Actinomyces become adult, and those few are almost certainly incapable of reproduction. Normal growth and moulting and egg production are resumed if the insects are re-infected with Actinomyces.