The mortality of Culex quinquefasciatus mosquitoes having fed ten days earl
ier on a chicken treated by 2 000 mu g/kg of ivermectin (about ten times th
e therapeutic dosage) is about 25% higher than the mortality recorded on mo
squitoes having fed on a non treated chicken. This systemic effect occurs o
nly if the blood meal takes place between 7 and 31 hours after the administ
ration of the drug. However no systemic effect is recorded either with the
C, quinquefasciatus mosquito or with the Simulium squamosum black fly when
they are fed on human beings treated at the therapeutic dose.