The National Institute of Allergy and Infectious Diseases (NIAID) and the Walter Reed Army Institute of Research (WRAIR) maintain phlebotomine sand fly colonies of mutual interest to be used as vector models in ongoing research on Leishmania-vector interactions, Leishmania transmission, diagnosis and control. Over a two-year period during 2004-2005, the principal working colonies at the WRAIR crashed, with populations dropping to such low levels that sand flies needed in critical research were unavailable. Upon examination, all of the colonies were found to be heavily infected with aseptate gregarines, presumably Ascogregarina chagasi. These parasites occur naturally in wild sand fly populations and appear to enjoy a commensal relationship with the sand fly. However, under conditions of mass rearing, high parsitemias can develop that lead to decreased longevity and fecundity and severe decline of the colony population. This study was initiated to examine the life cycle of the parasite in all sand fly life stages and to evaluate several methods for treating sand fly eggs to control it. These included washing with tap water, 1% Clorox, 1 % formal, and VirkonŽ, a broad spectrum disinfectant. Washing in 1% Clorox solution was found to be the most efficacious treatment.