Australian Journal of Entomology, 1997, 36: 287-292 287 Ecology of the Aedes australis (Erichson) 1842 Complex (Diptera: Culicidae) in Australia and New Zealand REINHART A. BRUST Department of Entomology, University of Manitoba, Winnipeg, Manitoba, R3T 2N2, Canada. Present address: #110 13860 70th Ave, Surrey, BC V3W OS1, Canada. ABSTRACT Most populations of Ae. australis developed their first egg batch without a blood- meal (autogeny), but the proportion of females that were autogenous was altered by environmental conditions. Low rearing temperatures were more favourable than high temperatures for autogenous egg development, when combined with a rich protein larval diet. Neither an adult carbohydrate meal nor mating were necessary for maximum autogenous egg production. Of five Tasmania collections examined, the proponion of autogenous females amongst the different populations ranged from 100% to 0%. In the autogenous Sydney, NSW, population, the addition of a blood-meal did not increase egg production in the first gonotrophic cycle. Introduction isolation was rare or absent amongst these The saline rock pool mosquito Aedes australis populations, and that they should be regarded as (Erichson) is a species complex which currently conspecific (Brust unpubl. data). consists of two species, Ae. australis and Aedes Most populations of Ae. australis are ashworthi@dwards) (Brust and Mahon 1997). Ae. autogenous, but females are known to feed on ashworthi occurs in Western Australia, it is humans in nature and have been reported as a pest anautogenous, and may have diverged from its in eastern Tasmania (Russell 1993). Females from sibling species Ae. australis in eastern Australia Tasmania and New Zealand have been infected in a previous era (Brust and Mahon 1997). Ae. experimentally with Ross River virus, and the NZ australis is distributed along the seacoast from the population was able to transmit the virus (Austin Queensland/New South Wales border south to and Maguire 1982; Kay and Aaskov 1989). The Victoria, including Tasmania and islands in the blood feeding habit, versus autogeny (production Bass Strait, and west to South Australia. It is also of eggs without blood) of Ae. australis should be present in Lord Howe and Norfolk Islands, and investigated from different parts of its distribution in New Zealand (Belkin 1968; Dobrotworsky 1966; to assess its potential as an arbovirus vector. Lee et al, 1984). From the number of collection To understand one aspect of the reproductive sites reported in the literature, and from the biology of the Ae. australis complex (viz. autogeny intensity of the populations at these sites, it versus anautogeny), nine populations from across appears that Tasmania is the geographical centre Australia and one from New Zealand were of Ae. australis in Australasia. Biological, examined for the ability of females to produce reciprocal crosses of a population from each of eggs when reared under laboratory conditions South Australia, New South Wales and New favourable to autogenous egg development. Zealand showed that post-mating reproductive Experiments were also conducted to investigate Fig. 1. Map of the sites from which larval populations of the Aedes australis complex were obtained. W-Wardang Island, SA; D-Devonport, L-Low Head, K-Kingston, M-Marrawah, Sw-Swansea, Tas; DU-Durras, G-Guerilla Bay, Sy-Sydney, NSW; P-Purakanui Bay, NZ. 288 R. A. BRUST separately the effects of environmental conditions, intervals were used to determine whether means an adult carbohydrate diet, mating, and blood- of wing length or egg numbers differed amongst feeding on egg development in autogenous females from different populations. females. Results Materials and methods When a population at Durras, NSW, developed Larval collections of Ae. australis were obtained under natural conditions in the field, there was a from Purakanui Bay (NZ), Sydney, Durras and difference in the proportion of autogenous females Guerilla Bay (NSW), Kingston, Swansea, Low that emerged at the peak of summer as compared Head, Devonport and Marrawah (Tas) and to the proportion of autogenous females that Wardang Island (SA) (Fig. 1). Larvae were emerged from the same pool at the peak of winter, transported by air or by road, and were reared when the temperatures were lower and under controlled environmental conditions in the development was slower. Females that emerged in laboratory. They were fed liver powder (ICN winter were larger; 85Vo of the females were Biomedicals, Ohio, USA) daily, in excess of autogenous in July, when the rock pool consumption, and were reared uncrowded in pans temperatures were low (10-18 "C), while only 40% 33 x 33 x 10 cm high. Pupae were removed and of the females were autogenous in January, when placed in clear acrylic cube cages either 32 cm or the rock pool temperatures were much higher 15 cm per side. The autogenous populations were (20-32°C). The number of eggs developed per stenogamous, and mated readily in either sized female was not statistically different between cage. Populations that were partially autogenous January and July (Table 1). or anautogenous mated readily when reared and When the Durras population was reared under maintained at 1618"C, and when more males than controlled environmental conditions of 26 "C and females were available. Adults were offered 10% 16L:8D, the adults were smaller, not all females sucrose, and anautogenous populations were fed were autogenous, and those that were autogenous on a human host. Wing length measurements laid fewer eggs than populations reared at 16 "C, provide a reliable estimate of body weight (mass) at either 16L:8D or 10L:14D (Table 2). The in mosquitoes (Siege1 et al. 1994), and wing length different photoperiods had no statistically of adult females was measured from the axillary significant effect on female size nor on the mean incision (Harbach and Knight 1980) to the apex number of eggs per female. of the wing, excluding the wing fringe scales. The number of autogenous eggs per female was Statistix@software (Tallahassee, Florida, USA) correlated with female size (RZ = 0.39, n = 29, was used for statistical analyses. Regression P < 0.002) (Fig. 2) in females of a Guerilla Bay, analysis was used to compare wing length against NSW population reared in the Iaboratory at 24 "C. egg numbers, wing length against latitude, and These laid from 58 to 167 eggs (mean 115.4) and latitude against proportion of autogenous females. wing length ranged from 3.6 to 4.2 mm (mean 4 Minimum and maximum 95 070 confidence mm) . Table 1. Autogeny in a natural population of Ae. australis from Durras, NSW. Pupae were collected in the field and the adults were maintained on 10% sucrose at 16"C, 10L:14D. Date of collection Mean WL1 Vo autogenous Mean no. of eggs 18 January 1995 3.2 (0.03) a* 40 35 (4.1) a 15 July 1995 3.8 (0.02) b 85 41 (3.6) a 'Wing length in mm; SEM in parentheses; N = 30hreatment. 'Different letters within a column indicate that the means are statistically different (95% C.I.). Table 2. Autogeny in a population of Ae. australis from Durras, NSW, under different controlled conditions in the laboratory. Conditions Mean WE To autogenous Mean no. of eggs 26°C. 16L:8D 3.8 (0.02) a' 85 91 (4.0) a 16"C, 16L:8D 4.4 (0.02) b 100 137 (5.0) b 16OC, 10L:14D 4.5 (0.02) b 100 126 (4.0) b 'Wing length in mm; SEM in parentheses; N = 30hreatment. 'Different letters within a column indicate that the means are statistically different (9SVo C.I.). Table 3. The effects of mating and of an adult sucrose (10%) meal on autogeny in the Sydney population of Ae. australis! Diet Mated Mean WL' 070 autoeenous Mean no. of eees Water No 4.5 (0.02j a 100 122 (2.5j a 'Rearing and maintenance 16T, 10L:14D. 'Wing length in mm; SEM in parentheses; N = 30heatment. 'The same letter within a column indicates that the means are not statistically different (95% C.I.). ECOLOGY OF THE AEDES AUSTRALIS COMPLEX 289 There was no effect on the expression of 5). The follicles were all developed to the egg stage, autogeny, nor on the number of eggs developed and there were no partially developed follicles in due to the presence or absence of a sucrose meal any of the blood-fed females. in females of a Sydney population. Similarly, matiug had no effect on the expression of Discussion autogeny, nor on the number of eggs developed (Table 3). Autogenous egg development in mosquitoes is When populations from different locations in influenced by genetics (O'Meara and Craig 1969; Australia and one from New Zealand were reared O'Meara 1972; Eberle and Reisen 1986), and maintained at environmental conditions environmental conditions for rearing and favourable to the expression of autogenous egg maintenance of the population (Spadoni et al. development, under the same larval and adult 1974; Brust 1991; Sota and Mogi 1995), nutrition food regimes, there was considerable variation in of the larvae (O'Meara and Krasnick 1970), the proportion of autogenous females in the carbohydrate diet of females (O'Meara and populations. The Wardang Island, Devonport and Petersen 1985) and presence or absence of mating Low Head females were anautogenous, whereas (O'Meara and Evans 1976). Since genetically the Marrawah females were 100% autogenous. autogenous females use stored lipoproteins for egg The Swansea collection consisted of 13% production, a high protein larval diet is favourable autogenous females and the collection from for maximum egg development in the adult female Kingston consisted of 5% autogenous females. (O'Meara and Krasnick 1970). Environmental The most southerly population studied was the one conditions influence the expression of autogeny from Purakanui Bay, NZ; it consisted of 4% in both Culex and Aedes species that possess the autogenous females.