Age grading Anopheles arabiensis: their gorging and surviving responses using a membrane feeding system.

Literature on artificial membrane feeding has traditionally supported the notion that mosquitoes have to be enough old to present a high gorging rate and enough young to present a high surviving rate. In order to know the best mosquito age to perform a Plasmodium sp. experimental infection revealed by oocyst examination, Anopheles arabiensis of known ages were fed on baudruche membrane with fresh human blood thermostated at 37 degrees C. The response was evaluated in term of gorging after ten minutes in contact with the membrane feeder and, for engorged females, in term of survival eight days after the engorgement. Two strains of mosquitoes were used, one wild, collected at larval stages in the city of Dakar and the other, originating from the same place but reared in our insectary since three years. The two strains showed their highest gorging rate at 3-4 days after emergence (39.4% for the wild strain and 63.3% for the insectary strain). The survival rate of the wild strain was highest at 2-3-4 days after emergence (64.8%) and those of the insectary strain at four days (65.6%). In conclusion, the gorging mosquitoes would have to be aged of 3-4 days after emergence for the wild strain and of four days for the insectary strain in order to obtain eight days after the engorging the best output of fed and surviving mosquitoes.