Blood feeding by Aedes notoscriptus (Skuse) (Diptera: Culicidae) on the brush-tailed possum, Trichosurus vulpecula (Kerr)

behaviour of New Zealand mosquitoes.A reason for the paucity of such research is the absence of vectors of human health concern such as Aedes aegypti (Linnaeus), A. albopictus (Skuse), Culex annulirostris Skuse and anophelines. In New Zealand, Miles et al. (1973) revealed the presence of Whataroa virus neutralizing antibody in birds, while Maguire et al. (1967) isolated a virus from Culiseta tonnoiri (Edwards) and Culex pervigilans Bergroth. Miles et al. (1971) considered that thrushes (Turdus philomelos Brehm) were the predominant host of this virus. Using the agar gel immunodiffusion method, Foot (1970) identified human and mouse blood in the stomachs of A. notoscriptus (Skuse). Arthropod-borne viruses by definition often cycle between haematophagous arthropods and vertebrates, including humans. The probability of vectors transferring pathogens increases if a susceptible host population is large. In Australia, Doherty (1972) considered wallabies and other marsupials to be the main vertebrate hosts of Ross River virus. This has important implications for New Zealand as the brush-tailed possum, Trichosurus vulpecula (Kerr) is one marsupial well established here, with a population estimated at 60 million (Batchelor & Cowan 1988). During 1996 we assessed blood feeding by A.notoscriptus on T. vulpecula in bush at Hellyers Creek forest reserve area (NZMS 260, R10; 36° 45’.79”S, 174° 42’.8”E) near Albany/Glenfield in Auckland. This area experiences mean temperatures ranging from 17.7°C in summer to 12.1°C in winter, while rainfall averages 563 mm and 832 mm during the same periods (Anon. 1996). The regenerating native bush has abundant habitats for possums and a number of mosquito species. Mosquitoes were caught inside possum-baited traps (Service 1993) made of mosquito netting set on a square frame (120 cm x 120 cm) and placed over a wire cage containing a possum. The netting was raised 20 cm from the ground allowing mosquitoes access to the possum. These were set over 25 trap nights in February, March, November and December 1996, and mosquitoes were frozen at -70°C until required for processing.Agar gel diffusion (Bull & King 1923, Crans 1969) was used to identify host blood from mosquitoes. To extract blood meals from an individual mosquito, the abdomen was placed on a glass slide with 70 μl of Dulbecco’s Phosphate Buffer Solution (PBS). A pair of fine forceps and a needle were then used to squeeze the abdomen at the 6th or 7th segment. The forceps were moved up the abdomen, forcing the stomach and its contents into the PBS. On most occasions it was necessary to break the peritrophic membrane and allow blood to mix with the PBS. Preparation of agar gel experiments follow the method of Crans (1969). Antisera were as used by Grigor et al. (1991). Antisera were tested for sensitivity to possum blood and an estimate of optimal proportions was made (Marrack 1963). The specificity of transferrin and serum albumin was tested against ten other animal species considered as possible sources of blood for mosquitoes, and found near the study area, i.e., human, dog, cat, horse, cow, pig, goat, sheep, rat and chicken. Possum blood was used as the control. After determining antisera optimal proportions, anti-possum serum albumin and transferrin were used at concentrations of 1:10 in PBS, and tested against animal blood at 1:2 in PBS. Fifty μl of each solution was pipetted into separate wells. Of the 170 A. notoscriptus dissected, 147 (86%) had taken a blood meal. All of these had fed on T. vulpecula. Serum albumin and transferrin showed no reactivity with sera of the 10 other animals, including human blood. Although other vertebrate species were present but were not tested, (e.g., geese, mice) the possibility of a mosquito feeding on them and then subsequent reaction with either sera after gel diffusion tests was considered unlikely.Also, no other marsupials were considered as possible hosts, as none had New Zealand Entomologist 24: 87–88 (December 2001)