Seasonal Abundance, Longevity and Population Age Composition of Potential Malaria Vectors in Northern and Southern Australia

Abstract

Populations of Anopheles mosquitoes were sampled fortnightly for 2 years at Casuarina and Leanyer in Darwin, N.T., and at Appin, N.S.W., and for 3 years at Echuca, Vic. Six anopheline species were recorded at the Darwin sites: An. bancroftii, An. farauti s.l., An. hilli, An. annulipes s.l., An. meraukensis and An. novaguinensis, although only the first three species were common and dissected for age grading. Only one species, An. annulipes s.l., was recorded at Appin and Echuca. The seasonal peak abundance of Anopheles species at Darwin was generally from the late wet season to the middle of the dry season. The proportion of the populations which was parous generally increased with increasing abundance. The oldest females were found in the early to mid-dry season about May, June and July. An average of 4.3% of An. farauti s.l., and an average of 2.6% of An. bancroftii, were old enough to be potential malaria vectors at Casuarina; at Leanyer less than 3.0% of An. farauti s.l., 0.1% of An. bancroftii, and 0.3% of An. hilli were of a potentially infective age. The period of greatest risk for malaria transmission in Darwin was, therefore, from April to August. At Appin and Echuca, populations of An. annulipes s.l. were present throughout the year, being most abundant in mid- to late summer. The populations aged gradually from the spring buildup; the oldest females being found from summer to late autumn. Females old enough to be potentially infective for malaria were recorded at each site during summer: up to 6.6% of the species at Appin and up to 10.3% at Echuca.