Lethal and sublethal effects of avermectin/milbemycin parasiticides on the African malaria vector, Anopheles arabiensis.

Four cattle parasiticides of the avermectin/milbemycin class were examined for lethal and sublethal effects on the zoophilic, African malaria vector Anopheles arabiensis. Ivermectin, moxidectin, doramectin, and eprinomectin were mixed with bovine blood and provided to laboratory-reared An. arabiensis in a membrane feeder. Ivermectin and eprinomectin were lethal to An. arabiensis at low concentrations (LC50s of 7.9 ppb and 8.5 ppb, respectively). While the lethality of doramectin (LC50 of 23.9 ppb), was less than that of ivermectin and eprinomectin, it markedly reduced egg development. The concentration of moxidectin required to reduce survivorship and egg production in An. arabiensis was > 100 fold greater than for ivermectin or eprinomectin. Moxidectin was weak in its actions against An. arabiensis relative to the other three chemicals. These results suggest that cattle treated with ivermectin or eprinomectin in the prescribed range of low dosages as parasiticides have blood toxic to zoophilic malaria vectors. Regionally coordinated, seasonal treatment of cattle could suppress An. arabiensis populations, thereby reducing malaria transmission. Doramectin (although less toxic) would have population level effects on egg production if used in this manner.