Effects of the avermectin analogue MK-243 on vitellogenesis and reproduction in the ixodid tick,Amblyomma hebraeum

A dose-dependent reduction in weight of total egg mass and a slightly increased oviposition latency were observed following injection of the avermectin, analogue MK-243 (4-epi-methylamino-4-deoxyavermectin B₁) directly into the haemocoel of engorged femaleAmblyomma hebraeum Koch (Acari: Ixodidae). Egg laying was almost completely inhibited at 100 g/kg body weight. MK-243 markedly inhibited ovary development and vitellogenesis. Ticks treated with 100 g MK-243/kg also had one-tenth the haemolymph ecdysteroid concentration compared to controls 10 days post-engorgement. Thus, among its other effects on ticks, the avermectins also inhibit the process of vitellogenesis.