Disappearance of malaria vector Anopheles sundaicus from Chilika Lake area of Orissa State in India

Malaria has declined around Chilika Lake (85°20′ E, 19°40′ N) in Orissa State, India, from hyperendemicity in the 1930s to hypoendemicity during recent decades. Six decades ago, 21 spp. of Anopheles mosquitoes (Diptera: Culicidae) were recorded from this area, including the well known Indian malaria vectors An. culicifacies Giles, An. fluviatilis James, An. maculatus Theobald, An. stephensi Liston and An. sundaicus (Rodenwaldt), the last formerly regarded as the main vector locally. Surveys of Chilika area during 1995–96 found 8 spp. of culicine plus 14 spp. of anopheline mosquitoes, the latter comprising An. subpictus Grassi sensu lato, An. hyrcanus (Pallas) s.l., An. vagus Dönitz, An. annularis van der Wulp s.l., An. culicifacies Giles s.l., An. aconitus Dönitz, An. varuna Iyengar, An. barbirostris van der Wulp s.l., An. philippinensis Ludlow, An. ramsayi Covell, An. jeyporiensis James, An. pallidus Theobald, An. tessellatus Theobald and An. karwari James in decreasing order of abundance. Among indoor‐resting female mosquitoes, the anthropophilic index was 4–7% and some species (An. culicifacies, An. subpictus, An. vagus) tended to enter houses for resting after blood‐feeding outside. Females of potentially infective age (three‐parous) were obtained for An. culicifacies (11%) and An. annularis (< 2%), the more abundant established vector in this coastal area, but not for small samples of An. subpictus and An. vagus. Anophelines reported previously but not found in our survey were An. fluviatilis, An. jamesii Theobald, A. maculatus, An. splendidus Koidzumi, An. stephensi, An. theobaldi Giles and the former main vector An. sundaicus.     

Differential ecology of Anopheles punctulatus and three members of the Anopheles farauti complex of mosquitoes on Guadalcanal, Solomon Islands, identified by PCR-RFLP analysis

From a series of larval collections made across northern Guadalcanal during the dry season, October–November 1997, four members of the Anopheles punctulatus group of mosquitoes (Diptera: Culicidae) were identified using PCR‐RFLP analysis. Anopheline larvae were found in 54/57 (95%) of the sites sampled, comprising An. farauti Laveran sensu stricto (32 sites), An. farauti species no. 2 (39 sites), An. farauti no. 7 (36 sites) and An. punctulatus Dönitz (10 sites). Anopheles punctulatus occurred only on the coastal plain, where it was associated with the more transient sites. Anopheles farauti sensu lato was more widespread throughout the survey region, with similar proportions of all three sibling species in both transient and permanent sites. Two members of the An. farauti complex, An. farauti s.s. and species no. 2, were found in brackish water. All breeding sites of An. punctulatus were cohabited by An. farauti s.l., sometimes by all three sibling species. Anopheles farauti s.s. was the only species collected on human bait, with a much higher biting rate early in the evening (57 bites/human/hour at 18.30–20.00 hours) than later (0.8 bites/human/hour at 21.00–24.00 hours).     

Multiple host feeding in field populations of Anopheles culicifacies and An. subpictus in Sri Lanka

A histological technique was used to detect the multiple blood-feeding of female mosquitoes, within the same gonotrophic cycle, in field populations of the malaria vectors Anopheles culicifacies and An. subpictus (Diptera: Culicidae) at a village in the low country of Sri Lanka, during 1994-96. Among 3306 An. culicifacies and 871 An. subpictus engorged females examined, respectively, 34.4% and 30.4% were multiple-fed. In these two species, double meals accounted for 92.7% and 89.5%, and triple meals for 7.3% and 10.5% of multiple meals, respectively. More females of An. culicifacies (53.7%) than An. subpictus (44.5%) multiple-fed on different nights. Multiple feeding rates in the two species were independent of sample size and field abundance. In An. culicifacies, but not An. subpictus, these rates were proportional to ambient temperature but not to humidity. Bloodmeal ELISA showed that 8.3% of 242 An. culicifacies were human-fed and 80% of these (i.e. 6.6%) were concurrently bovid-fed. Combining the histological and ELISA data, it was estimated that multiple feeding involving a human host had occurred in 7.2% of the blood-feeding An. culicifacies population at this study site. Only 1.2% of 406 An. subpictus were human-fed and all of these were concurrently bovid-fed. Multiple bloodfeeding within the same gonotrophic cycle was attributed to a local 'frequent feeding strategy' in these primarily zoophagic and endophilic malaria vectors. Unfortunately this strategy enhances their human-biting rate and hence their vectorial capacity.     

Use of rDNA-PCR to investigate the ecological distribution of Anopheles bwambae in relation to other members of the An.gambiae complex of mosquitoes in Bwamba County, Uganda

Abstract Environmental relationships were investigated among three species of the Anopheles gambiae complex of mosquitoes associated with the geothermal springs located in Bwamba County, Uganda. The degree of ecological isolation between An.gambiae and An. bwambae, a sibling species known only from the geothermal springs environment, was assessed on the basis of adult distribution and abundance as well as differences in larval habitats. Field data were gathered during June 1995 without knowing which of the species were being collected. Specimens identified subsequently by rDNA-PCR were used to interpret the ecological data. Ten of twenty aquatic sites sampled were found positive for immature stages of the An.gambiae complex. Larvae of An.bwambae were associated with ‘springwater’ habitats having much higher conductivity, much greater concentrations of dissolved solids and slightly higher temperature and pH than ‘normal’ fresh water sites inhabited by larvae of An.gambiae. Larval habitats of both species were unshaded: An.bwambae occurred among dense sedge (Cyperus laevigatus) whereas those of An.gambiae were almost devoid of vegetation. One mixed sample showed that larvae of both species occur together in peripheral aquatic sites with intermediate physical and ecological characteristics. In water preference tests, free-flying females were reluctant to lay eggs on bowls of water in cages; gravid females (with one wing amputated) placed on the surface of water in a cup laid eggs on seasoned rainwater (12/51 An.bwambae; 2/3 An.gambiae) as well as spring-water (39/51 An.bwambae; 1/3 An.gambiae). All three An.gambiae oviposited on the first water option, whereas 86% of An. bwambae witheld oviposition until being moved to the other type of water after 5–6 h, and 82% (36/44) of these laid eggs on geothermal water in preference to rainwater. Larval and adult collections showed that An.gambiae occurs sympatrically with An.bwambae throughout its range in the humid foothill environment of the geothermal springs, whereas the distribution of An.arabiensis overlaps only slightly with An.bwambae towards the savanna environment north of the springs.