The rotation of the male terminalia of Aedes aegypti mosquitoes was investigated with chemical surgical, and mechanical methods. Neither decapitation nor ventral nerve cord transection affected the postemergence rotation, but methoprene administered to 4th-instar larvae and early instar pupae slowed rotation significantly and, in the case of pupal treatment, also interfered with successful insemination. Methoprene appeared to interfere with the developmental maturation of the cross muscles located between the 7th and 8th abdominal segment and postemergence nervous or humoral signals did not appear to affect this rotation.