THE INFLUENCE OF MICROFILARIAL DENSITY OF DOG HEARTWORM DIROFILARIA-IMMITIS ON INFECTION-RATE AND SURVIVAL OF AEDES NOTOSCRIPTUS AND CULEX ANNULIROSTRIS FROM AUSTRALIA

The mosquitoes Aedes notoscriptus and Culex annulirostris, previously shown to be competent vectors of Dirofilaria immitis,were allowed to f eed on dogs with densities of microfilariae ranging from 2665 to 33,05 5 microfilariae/ml. Filaria developed in both species at a similar rat e independent of the initial microfilarial density. Cx annulirostris i ngested more microfilariae although the number of developing larvae wa s consistently greater in Ae.notoscriptus; one female Ae.notoscriptus carried sixty-two third-stage larvae 10 days after feeding, although n o more than twelve were found in Cx annulirostris. The mortality rate of Ae.notoscriptus in the first 3 days of filarial development was rel ated to increasing microfilarial density, and was greater than that of Cx annulirostris, which quickly reduced its worm load and survived wi th fewer third-stage larvae but for longer than Ae.notoscriptus. The v ector efficiency index was higher at all microfilarial densities for A e, notoscriptus, but its survival was much reduced, and therefore Cx a nnulirostris may be the more effective vector in localities where dogs have very high parasitaemias.