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 feed on dogs with densities of microfilariae ranging from 2665 to 33,055 microfilariae/ml. Filaria developed in both species at a similar rate independent of the initial microfilarial density. Cx annulirostris ingested more microfilariae although the number of developing larvae was consistently greater in Ae.notoscriptus; one female Ae.notoscriptus carried sixty-two third-stage larvae 10 days after feeding, although no more than twelve were found in Cx annulirostris. The mortality rate of Ae.notoscriptus in the first 3 days of filarial development was related to increasing microfilarial density, and was greater than that of Cx annulirostris, which quickly reduced its worm load and survived with fewer third-stage larvae but for longer than Ae.notoscriptus. The vector efficiency index was higher at all microfilarial densities for Ae.notoscriptus, but its survival was much reduced, and therefore Cx annulirostris may be the more effective vector in localities where dogs have very high parasitaemias.