Host feeding patterns of Anopheles culicifacies species A and B

Countercurrent immunoelectrophoresis was used to assay bloodmeals to determine the host specificity of Anopheles culicifacies species A and B, collected from areas in Delhi, Uttar Pradesh and Bihar. Results indicated the predominantly zoophagic nature of species A and B with a relatively higher degree of anthropophagy for species A. Further, the human blood index was found to be related to the proportion of human and cattle population in an area. This study is significant because, of the two species only species A was incriminated as the vector of malaria in these areas.     

Occurrence of Anopheles culicifacies species A in Iran

Polytene chromosome preparations of the ovarian nurse cells of Anopheles culicifacies females collected in 6 different parts of Baluchistan, Iran, during September-October 1987 and May-June 1988 revealed the existence of species A in this country. The chromosome arms are homosequential with those of species A of India. This report confirms the distribution of species A in Iran.     

Linkage studies on DDT and dieldrin resistance in species A and species B of the Anopheles gambiae complex

Linkage studies in A. gambiae species A showed that the two autosomal markers diamond (Di) and collarless (c) belonged to different linkage groups: Di on linkage group 2 and c on linkage group 3. With the aid of the two markers it was possible to establish the linkage relationship between the genes for DDT resistance and for the two types of dieldrin resistance. The DDT resistance gene in species A assorted independently of c and was found to be linked with Di at a map distance of 26.3 units. The genes for the two types of dieldrin resistance, dominant and incompletely dominant, were found to be allelic. The major gene for dieldrin resistance was shown to be linked with the gene for DDT resistance in linkage group 2 at a map distance of 35.3 units. This suggested that Di and the dieldrin resistance gene were some 61.6 units apart.     

Susceptibility of Anopheles culicifacies species A and B to Plasmodium vivax and Plasmodium falciparum as determined by immunoradiometric assay

We have used a two-site immunoradiometric assay and species-specific antisporozoite monoclonal antibodies to determine the relative roles that sibling species A and B of the Anopheles culicifacies complex play in malaria transmission in western Uttar Pradesh, India. The results unequivocally establish species A as the primary vector of both Plasmodium vivax and P. falciparum in this area. Our results indicate active transmission of P. vivax from May to October and of P. falciparum from August to December. The identification of species A as the primary malaria vector in northern India will now allow suitable malaria control strategies to be designed.     

Resistance in Anopheles culicifacies sibling species B and C to malathion in Andhra Pradesh and Gujarat States, India

Studies conducted in Warangal, Khammam and Mahabubnagar districts in Andhra Pradesh and Surat district in Gujarat have revealed that Anopheles culicifacies sensu lato (s.l.) populations were resistant to malathion. In the absence of indoor spraying of malathion in public health programs in the 3 districts of Andhra Pradesh, resistance is attributed to the extensive use of pesticides in agriculture. Species B and C were sympatric in all areas surveyed, and both the species were resistant to malathion. In most of the surveys carried out in Mahabubnagar, Khammam and Warangal, levels of resistance were higher in species C than in B. In Mahabubnagar district an increase in resistance from 5.5 to 64% was observed from 1985 to 1987 in An. culicifacies s.l. The proportion of species C was low in the initial 2 surveys, and in the later surveys the proportion was almost equal to that of species B; the resistance level was also significantly higher than in species B. In Surat district, where resistance ranged from 74 to 93%, the level of resistance in the 2 species was almost the same.     

Anopheles culicifacies: siblings species composition and its relationship to malaria incidence

Entomological and epidemiological surveys in May, August and November 1985 and March 1986 were conducted in villages in Bulandshahr, a western district in Uttar Pradesh and in three eastern districts, Jaunpur, Ballia and Saran. In Bulandshahr, Anopheles culicifacies sibling species A and B were found, with a predominance of species A. Both Plasmodium vivax and P. falciparum were present and the malaria incidence remained high (SPR, 6-50%) indicating an active transmission. In contrast, in three eastern districts predominance of species B with an occasional occurrence of species A was observed. Malaria cases were almost absent in Ballia and Saran and in Jaunpur 10.3% slide positivity rate was observed in May but in later surveys cases were considerably lower (SPR, 0.5-2.9%) indicating the absence of indigenous transmission. In the eastern districts, malaria parasites are regularly brought in from endemic areas by the migrant labor population. Although An. culicifacies s.l. occurs in both the areas, the difference in malaria incidence appears to be due to the difference in the composition of the sibling species which is, the predominant presence of species A in the western district and its absence in eastern districts. This indicates that species A is responsible for active malaria transmission while species B is not.     

Follow-up studies after withdrawal of deltamethrin spraying against Anopheles culicifacies and malaria incidence

Follow-up studies were carried out from 1989 to 1998 after withdrawal of deltamethrin indoor spraying to evaluate the recovery rate of a population of Anopheles culicifacies resistant to dichlorodiphenyltrichloroethane (DDT) and hexachlorocyclohexane (HCH) in selected villages in Uttar Pradesh State, India. The study revealed 82.4-96.5% reduction in adult density of An. culicifacies and 72.7-96% reduction in malaria incidence in the area sprayed with deltamethrin at 20 mg/m2 as compared to a control area sprayed with HCH, for 5 successive years even after withdrawal of deltamethrin spray. The impact was very clear when the annual falciparum incidence was compared with that of the control area. The vector population gradually started recovering after 5 years. However, the slide falciparum rate remained below 4 even after 10 years of withdrawal of spraying. The study revealed that indoor residual spraying of deltamethrin would be cost-effective, at least in areas where malaria is transmitted by An. culicifacies, which is primarily a zoophilic species and associated with malaria epidemics. In view of this, a review of the insecticide policy and strategy of vector control is urgently needed because of the possible risks associated with the presence of nonbiodegradable insecticide in the environment, as well as to minimize the costs of operation and to enhance the useful life of insecticides.     

Tests for the existence of genetic variability in the tendency of Anopheles culicifacies species B to rest in houses and to bite man

Experiments were carried out in Sri Lanka on the malaria vector Anopheles culicifacies using the mark—release—recapture technique. Collections were made in cattle-baited huts fitted with exit traps, and in nightbiting catches on human subjects. The same individual mosquitos were caught biting cattle and man on different occasions and the numbers caught demonstrated an overall preference for the cattle. The mean interval between successive blood meals in the field was estimated to be 2.3 days.     

Cytogenetic evidence for a fifth species within the taxon Anopheles dirus in Thailand

Crossbreeding and chromosomal evidence are presented for the existence of a fifth sibling species within the taxon of Anopheles dirus in Thailand. The new species is morphologically identifiable as Anopheles balabacensis "Fraser's Hill form." Structural differences in mitotic chromosomes and extensive asynapsis in hybrid polytene chromosomes indicate that significant genetic divergence exists between this species and its closest relatives, An. dirus species A, B, C and D and An. balabacensis.     

Spatiotemporal distribution of insecticide resistance in Anopheles culicifacies and Anopheles subpictus in Sri Lanka

The malaria situation in Sri Lanka worsened during the 1990s with the emergence and spread of resistance to the drugs and insecticides used for control. Chloroquine resistance has increased rapidly over this period, but adverse changes in malaria transmission are more closely associated with insecticide use rather than drug resistance. Insecticide susceptibility tests were routinely carried out in key anopheline vectors across the country for more than a decade. These sentinel data were combined with data collected by other research programmes and used to map the spatial and temporal trends of insecticide resistance in the main vectors, Anopheles culicifacies and A. subpictus, and to examine the relationship between insecticide resistance, changes in national spraying regimens and malaria prevalence. Both species had widespread resistance to malathion, the insecticide of choice in the early 1990s. Both species were initially susceptible to the organophosphate and pyrethroid insecticides used operationally from 1993, but some resistance has now been selected. The levels of malathion and fenitrothion resistance in A. subpictus were higher in some ecological regions than others, which may be related to the distribution of sibling species, agricultural pesticide exposure and/or environmental factors. The study highlights that the emergence and spread of insecticide resistance is a constant threat and that active surveillance systems are vital in identifying key vectors and evidence of resistance.     

Studies on Anopheles fluviatilis and Anopheles culicifacies sibling species in relation to malaria in forested hilly and deforested riverine ecosystems in northern Orissa, India

In a malaria-endemic region in northwestern Orissa, India, a longitudinal study was undertaken to delineate information on the sibling species of Anopheles fluviatilis and Anopheles culicifacies and their bionomics and role in malaria transmission in forested and deforested ecosystems. In forested villages, An. fluviatilis sibling species S (97.97%) and T (2.02%) were present. The former was highly anthropophagic (human blood index 0.88). Among the sibling species of An. culicifacies, species B (27.96%), C (71.1%), and B/C heterozygotes (0.94%) were present and were highly zoophagic. In deforested riverine villages An. fluviatilis was nearly absent and An. culicifacies sibling species A (0.48%), B (21.1%), C (77.94%), and B/C heterozygotes (0.48%) were present. In forested villages, the annual parasite incidence (269 cases/1,000) and the slide positivity rate (45%) were significantly higher than those in deforested areas, which had values of 39 cases/1,000 and 27%, respectively. The study showed that the high endemicity of malaria in the forested villages was due primarily to 2 vectors, the high rate of anthropophagy of An. fluviatilis species S, and also the more favorable ecological conditions for this vector.     

Food of larval Anopheles culicifacies and Anopheles varuna in a stream habitat in Sri Lanka

No previous studies have been conducted on the natural food of larval Anopheles culicifacies s.l. (the major malaria vector) and An. varuna (a secondary vector) in Sri Lanka. The present study analyzed the contents of guts dissected from larvae collected from pools in a natural stream-cum-irrigation conveyance channel in the Upper Yan Oya watershed in the North Central Province of the country during August-September 1997 and July 1998. Determinations of physicochemical and biological parameters of the pools and their water were done at the same time. A fluorochromatic stain, 4',6-diamidino-2-phenylindole, was used to stain larval gut contents. Quantitative estimates of different categories of food types were made by analyzing the gut contents of 95 An. culicifacies (26 second instars and 69 fourth instars) and 52 An. varuna (21 second instars and 31 fourth instars). Detritus was the most frequent food type, comprising >74% of the gut contents in both species. Other food types included bacteria (cocci and rods), filamentous algae, diatoms, and desmids. Overall, bacteria constituted a significantly higher proportion of the gut contents in An. culicifacies than in An varuna. Significantly more detritus, bacteria, and total particulate matter occurred in 4th instars of An. culicifacies than in An. varuna, indicating a greater food intake in the former species. Second instars of An. culicifacies and An. varuna did not differ significantly in any parameter. A significant increase in food intake between 2nd and 4th instars was seen for An. culicifacies, but not An. varuna. Food indices were lower in An. varuna than in An. culicifacies when the 2 species co-occurred, indicating competition for food, and the implications of this to adult body size, survival, and fecundity are discussed.     

Observations on the swarming and mating behavior of Anopheles culicifacies Giles in nature.

The mating and swarming behaviour of A. culicifacies Giles was investigated during December 1975 at a cattle shed near the village of Sattoki, Lahore District, Punjab, Pakistan. On average, swarming commenced 20.9 min before sunset (light intensity 1414.4 lx) and ended 21.0 min after sunset (5.4 lx) with pairing restricted to the period from 6.1 min before (467.2 lx) to 15.8 min after sunset (26.9 lx). The swarms were principally composed of males, with females entering only for mating. On average, copulation lasted 27.2 s and was completed in flight. Most females (71.8%) collected while mating had taken a partial blood meal either the previous evening or on the same evening as mating. All females in the swarms were nulliparous and 82.6% had ovaries developed to at least Christophers'' stage IIa.     

Efficacy of PermaNet 2.0 against Anopheles culicifacies and Anopheles stephensi, malaria vectors in India

Bioefficacy of PermaNet was evaluated in both the laboratory and field against Anopheles culicifacies and An. stephensi, major malaria vectors in India. Contact bioassays were carried out after repeated washings and ring net bioassays to determine the median knockdown time of mosquitoes. Three villages were selected for the field trial: in the 1st village PermaNets were distributed, in the 2nd village untreated nets were distributed, and the 3rd village was a control. Entomological data were collected using standard procedures. The PermaNet contact bioassays showed high mortality (>80%) even after 20 washes against both the vector species. The median knockdown time of An. culicifacies and An. stephensi was 392 and 480 sec when exposed to fresh PermaNets and 472 and 986 sec when exposed to PermaNets that had been washed 20 times, respectively. PermaNets showed high efficacy in reducing the person-vector contact as evidenced by reduced person-hour density in the PermaNet village. Long-term field trials are indicated to test the impact of use of PermaNets in controlling malaria.     

Genetic and linkage analyses of dieldrin resistance in Anopheles culicifacies Giles

Genetic analysis indicates that dieldrin resistance in laboratory colonies of Anopheles culicifacies is under the control of codominant alleles of a locus in linkage group 3 (chromosome 3), approximately 31 map units from Acph (acid phosphatase).     

Resting behavior and malaria vector incrimination of Anopheles stephensi in Goa, India

Malaria in Goa, India, has been endemic ever since an outbreak occurred in 1986. Anopheles stephensi Liston has always been suspected as a malaria vector in this area. Due to lack of knowledge on its resting behavior, sufficient adult females could not be collected and incriminated as vectors in the past. In this study mosquito collections were conducted in three endemic urban and suburban areas of Goa. In well-built houses, 67 h of collections did not yield a single An. stephensi mosquito, although other species were encountered. However, collections in construction sites and workers' huts for 151 h yielded, besides other mosquito species, 38 An. stephensi females resting in 15 types of sites at a height varying from 30 cm to 2.4 m. Of the 37 of these mosquitoes tested for the presence of circumsporozoite protein (CSP) by an ELISA technique, 1 was found to be Plasmodium falciparum CSP positive.     

Inheritance of DDT resistance in species A and B of the Anopheles gambiae complex

It has been reported that Anopheles gambiae species A is resistant to DDT in Upper Volta and Togo, and DDT resistance has been found in a Sudan strain of species B. The species A strain from Upper Volta was more resistant to DDT than the Togo strain, while the Sudan strain of species B was the least resistant. The expression of resistance is genetically determined, and studies on the mode of inheritance have shown that resistance is inherited as a single dominant gene in the Togo strain of species A and the Sudan strain of species B, but that it is inherited as a single incompletely dominant gene in the Upper Volta strain of species A.