Repellent effects on Anopheles arabiensis biting humans in Kruger Park, South Africa

Abstract. Distribution of biting sites on the human body by the malaria vector Anopheles arabiensis Patton (Diptera: Culicidae) was investigated near a source of mosquitoes in the Kruger National Park, South Africa. Eight adult male volunteers (2 teams × 2 pairs of subjects) conducted human bait collections while seated on camp chairs in the open-air, wearing only short trousers (no shirt, socks or shoes). Mosquito collections during 18.30–22.30 hours on five consecutive nights in April 1998 yielded a total of 679 An. arabiensis females biting subjects with or without their ankles and feet treated with deet insect repellent (15% diethyl-3-methylbenzamide, Tabard™ lotion). On subjects whose feet and ankles were smeared with repellent, 160 An. arabiensis females were captured biting in 60 man-hours: 88.1% on the legs, 1.4% on the arms and 1.2% on other parts of the body, but none on the repellent-treated feet or ankles. On subjects without repellent treatment, 519 An. arabiensis were caught biting in 60 man-hours: 81.1% on feet and ankles, 16.4% on legs, 1.4% on arms and 1.2% on the rest of the body. For individual subjects, the reduction of An. arabiensis bites ranged from 36.4 to 78.2% (mean protection 69.2%). Results of this study confirm previous findings that, in this part of South Africa − inhabited only by wildlife − when people sit outside during the evening An. arabiensis prefers to bite their lower limbs: 97.5% below the knees. Overall, the number of bites by the malaria vector An. arabiensis was reduced more than three-fold (from 26 to 8/person/evening), simply by treating ankles and feet with a consumer brand of deet repellent. Whether or not this provides a satisfactory degree of protection against malaria risk would depend on the malaria sporozoite rate in the malaria vector population.     

Sexual competitiveness of a transgenic sexing strain of the Mediterranean fruit fly, Ceratitis capitata

The sterile insect technique (SIT), when used for the control of the Mediterranean fruit fly (medfly), Ceratitis capitata (Wiedemann) (Diptera: Tephritidae), generally relies on the release of sterile flies of only the male sex. Male selection is achieved through the use of a genetic sexing strain (GSS) in which females are killed by heat treatment in the generation prior to release. Transgenic sexing strains (TSS) have been developed that perform the same function of female-lethality, this time by withholding tetracycline (or related compounds) from the larval diet. The use of TSS may allow for certain problems associated with conventional GSS, such as strain instability and reduced productivity in mass-rearing, to be avoided. The performance, and principally the sexual competitiveness, of released male flies is important for the success of an SIT control programme. This study describes field cage experiments in which the competitiveness of males from a TSS (OX3376B) was compared with that of a conventional GSS (VIENNA-8) and two wild-type strains (TOLIMAN and ARG). When competing for female mates with wild-type males, OX3376B male performance was acceptable. When OX3376B males competed directly for mates with VIENNA-8 males, VIENNA-8 slightly outperformed the TSS males. Parallel tests, in which wild-type males competed with either OX3376B or VIENNA-8 males, showed that males from both sexing strains were highly competitive with wild-type males. These results suggest that OX3376B in particular, and TSS in general, show sufficiently good mating competitiveness to merit further research into their suitability for eventual use in SIT programmes.     

Population genetic structure of the malaria mosquito Anopheles arabiensis across Nigeria suggests range expansion

Ten microsatellite loci, four located within and six outside chromosome inversions, were employed to study the genetic structure of Anopheles arabiensis across the ecological zones of Nigeria (arid savannah in the north gradually turns into humid forest in the south). Regardless of location within or outside inversions, genetic variability at all loci was characterized by a reduction in both the number of alleles per locus and heterozygosity from savannah to forest. Across all loci, all but one allele in the forest also occurred in the savannah, whereas at least 78 alleles in the savannah were missing in the forest. Genetic differentiation increased with geographical distance; consequently, genetic distances between zones exceeded those within zones. The largest genetic distances were between localities at the extremes of the transect (range F(ST) = 0.196-0.258 and R(ST) = 0.183-0.468) and were as large as those between A. arabiensis and Anopheles gambiae s.s. Gene flow across the country was very low, so that Nm between the extremes of the transect was < 1. These data suggest that A. arabiensis has extended its range from the savannah into the forest during which it experienced a reduction in effective population size due to sequential founder effects. Gene flow post range expansion appears too restricted by geographical distance to homogenize the gene pool of A. arabiensis across Nigeria.     

Reduced susceptibility to DDT in field populations of Anopheles quadriannulatus and Anopheles arabiensis in Malawi: evidence for larval selection

Abstract.  Bioassays for insecticide resistance in adult mosquitoes were conducted on samples of Anopheles gambiae Giles s.l . (Diptera: Culicidae) species collected as larvae from breeding sites in the lower Shire Valley, Malawi. The results indicate full susceptibility to permethrin, deltamethrin and malathion, but reduced susceptibility to DDT in one sample from Thom (LT₅₀ of 8.39 min for females and 25.09 min for males). Polymerase chain reaction-based species identification of the mosquitoes assayed revealed a mixture of Anopheles arabiensis Patton and Anopheles quadriannulatus (Theobold). The LT₅₀ did not differ significantly between species. Genotyping of the L1014F and L1014S kdr alleles showed all mosquito specimens to be homozygous wild type; thus the reduced susceptibility detected is not attributable to target site insensitivity and instead is likely to be metabolic in nature. Anopheles quadriannulatus is characteristically zoophagic and exophilic. Indeed, of 82 Anopheles collected through knockdown collections within dwellings, only one was An. quadriannulatus and the rest were An. arabiensis . They are unlikely, therefore, to have been exposed to selection pressure arising from insecticide-treated net usage or to DDT indoor residual spraying. Therefore, it is suggested that this example of reduced susceptibility to DDT in An. quadriannulatus reflects selection in the larval stages.     

橘小实蝇遗传性别品系的建立及雄性不育技术

为了更好地应用昆虫不育技术防治橘小实蝇,建立了以蛹色区分雌雄性别的橘小实蝇遗传性别品系。经过连续测交表明遗传品系能稳定遗传。质量监测表明遗传性别品系平均孵化率、蛹重、羽化率、飞出率、存活率等指标与普通种无显著差异。取遗传性别品系羽化前1、2、3天（分别用-1 d、-2 d、-3 d表示）的雄蛹,经过100 Gy的⁶⁰Co辐射后,分别与野生雌虫杂交,F1代卵的孵化率均大大低于对照组。对经过辐射处理-1 d、-2 d、-3 d的雄蛹分别进行质量检测,飞出率、存活率与对照组均无显著差异;-1 d、-2 d的羽化率之间及与对照组之间无显著差异,-3 d的羽化率与-1 d、-2 d及对照组差异均显著。取遗传性别品系的-2d的雄蛹辐射100 Gy的⁶⁰Co,获得不育雄虫,和野生雄虫一起竞争与野生雌虫交配的机会,相对不育系数为0.4923,表明不育雄虫与野生雄虫交配能力相当。田间扩散能力研究表明,不育雄虫在田间存在丰富的寄主植物的情况下不会大量扩散很远的距离。     

Anopheles arabiensis and An. quadriannulatus resistance to DDT in South Africa

The malaria control programme of KwaZulu‐Natal Province, South Africa, includes Mamfene and Mlambo communities. Western‐type houses there are currently sprayed with deltamethrin, whereas traditional houses are sprayed with DDT for malaria control. In 2002, mosquitoes of the Anopheles gambiae complex (Diptera: Culicidae) were collected from DDT‐sprayed houses, by window exit traps, and from man‐baited nets outdoors. Larval collections were also carried out at Mzinweni Pan near Mlambo. Species of the An. gambiae complex were identified by rDNA polymerase chain reaction assay. The majority of samples collected by window trap and baited nets were identified as the malaria vector An. arabiensis Patton, with a few An. merus Dönitz and An. quadriannulatus (Theobald). The larval collections were predominantly An. quadriannulatus with a small number of An. arabiensis. Standard WHO insecticide susceptibility tests using 4% DDT and 0.05% deltamethrin were performed on both wild‐caught females and laboratory‐reared progeny from wild‐caught females. Wild‐caught An. arabiensis samples from window traps gave 63% and 100% mortality 24‐h post‐exposure to DDT or deltamethrin, respectively. Wild‐caught An. arabiensis samples from man‐baited net traps gave 81% mortality 24‐h post‐exposure to DDT. The F₁ progeny from 22 An. arabiensis females showed average mortality of 86.5% 24‐h post‐exposure to DDT. Less than 80% mortality was recorded from five of these families. Biochemical analyses of samples from each of the families revealed comparatively high levels of glutathione‐S‐transferases and non‐specific esterases in some families, but without significant correlation to bioassay results. Wild‐caught An. quadriannulatus larvae were reared through to adults and assayed on 4% DDT, giving 47% (n = 36) mortality 24‐h post‐exposure. Finding DDT resistance in the vector An. arabiensis, close to the area where we previously reported pyrethroid‐resistance in the vector An. funestus Giles, indicates an urgent need to develop a strategy of insecticide resistance management for the malaria control programmes of southern Africa.     

Evidence for late Pleistocene population expansion of the malarial mosquitoes, Anopheles arabiensis and Anopheles gambiae in Nigeria

Anopheles gambiae Giles s.s. and Anopheles arabiensis Patton (Diptera: Culicidae) are major vectors of malaria in Nigeria. We used 1115 bp of the mitochondrial COI gene to assess their population genetic structures based on samples from across Nigeria (n = 199). The mtDNA neighbour-joining tree, based on F(ST) estimates, separated An. gambiae M and S forms, except that samples of An. gambiae M from Calabar clustered with all the An. gambiae S form. Anopheles arabiensis and An. gambiae could be combined into a single star-shaped, parsimonious haplotype network, and shared three haplotypes. Haplotype diversity values were high in An. arabiensis and An. gambiae S, and intermediate in An. gambiae M; all nucleotide diversities were relatively low. Taken together, patterns of haplotype diversity, the star-like genealogy of haplotypes, five of seven significant neutrality tests, and the violation of the isolation-by-distance model indicate population expansion in An. arabiensis and An. gambiae S, but the signal was weak in An. gambiae M. Selection is supported as an important factor shaping genetic structure in An. gambiae in Nigeria. There were two geographical subdivisions in An. arabiensis: one included all southern localities and all but two central localities; the other included all northern and two central localities. Re-analysing an earlier microsatellite dataset of An. arabiensis using a Bayesian method determined that there were two distinctive clusters, northern and southern, that were fairly congruent with the mtDNA subdivisions. There was a trend towards decreasing genetic diversity in An. arabiensis from the northern savannah to the southern rainforest that corroborated previous data from microsatellites and polytene chromosomes.     

Characteristics of Anopheles arabiensis larval habitats in Tubu village,Botswana

Documented information on the ecology of larval habitats in Botswana is lacking but is critical for larval control programs. Therefore, this study determined the characteristics of these habitats and the influences of biotic and abiotic factors in Tubu village, Botswana. Eight water bodies were sampled between January and December, 2013. The aquatic vegetation and invertebrate species present were characterized. Water parameters measured were turbidity (NTU), conductivity (μS/cm), oxygen (mg/l), and pH. Larval densities of Anopheles arabiensis mosquitoes and their correlation with abiotic factors were determined. Larval breeding was associated with ‘short’ aquatic vegetation, a variety of habitats fed by both rainfall and flood waters and sites with predators and competitors. The monthly mean (± SE_mean) larval density was 8.16±1.33. The monthly mean (±SE_mean) pH, conductivity, oxygen, and turbidity were 7.65±0.13, 1152.834±69.171, 5.59±1.33, and 323.421±33.801, respectively. There was a significant negative correlation between larval density and conductivity (r = ‐0.839; p < 0.01), while a significant positive correlation occurred between turbidity and larval density (r = 0.685; p < 0.05). Oxygen (r = 0.140; p > 0.05) and pH (r = 0.252; p > 0.05) were not correlated with larval density. Floods and diversified breeding sites contributed to prolonged and prolific larval breeding. ‘Short’ aquatic vegetation and predator‐infested waters offered suitable environments for larval breeding. Turbidity and conductivity were good indicators for potential breeding places and can be used as early warning indices for predicting larval production levels.     

Genetic sexing strains in medfly,Ceratitis capitata,sterile insect technique programmes

The introduction of genetic sexing strains (GSS) into medfly, Ceratitis capitata(Wiedemann), sterile insect technique (SIT) programmes started in 1994 and it was accompanied by extensive evaluation of the strains both in field cages and in open field situations. Two male-linked translocation systems, one based on pupal colour, wp, and the other based on temperature sensitivity, tsl, have been used in medfly SIT programmes and they have quite different impacts on mass rearing strategy. In strains based on tsl, female zygotes are killed using high temperature and for wpstrains, female and male pupae are separated based on their colour. In all these systems the colony females are homozygous for the mutation requiring that the mutation is not too deleterious and the males are also semi-sterile due to the presence of a male-linked translocation. Managing strain stability during large-scale mass rearing has presented some problems that have been essentially solved by selecting particular translocations for GSS and by the introduction of a filter rearing system (FRS). The FRS operates by removing from the colony any recombinant individuals that threaten the integrity of the strain. The use of GSS opens up the possibility of using the SIT for suppression as opposed to eradication and different radiation strategies can be considered. Some of the many field trials of the strains that were carried out before the strains were introduced into operational programmes are reviewed and an overview is given of their current use.     

Pyrethroid resistance in Anopheles gambiae s.s. and Anopheles arabiensis in western Kenya: phenotypic,metabolic and target site characterizations of three populations

Field and laboratory investigations revealed phenotypic, target site and metabolic resistance to permethrin in an Anopheles gambiae s.s. (Diptera: Culicidae) population in Bungoma District, a region in western Kenya in which malaria is endemic and rates of ownership of insecticide‐treated bednets are high. The sensitivity of individual An. gambiae s.l. females as indicated in assays using World Health Organization (WHO) test kits demonstrated reduced mortality in response to permethrin, deltamethrin and bendiocarb. Estimated time to knock‐down of 50% (KDT₅₀) of the test population in Centers for Disease Control (CDC) bottle bioassays was significantly lengthened for the three insecticides compared with that in a susceptible control strain. Anopheles arabiensis from all three sites showed higher mortality to all three insecticides in the WHO susceptibility assays compared with the CDC bottle assays, in which they showed less sensitivity and longer KDT₅₀ than the reference strain for permethrin and deltamethrin. Microplate assays revealed elevated activity of β‐esterases and oxidases, but not glutathione‐S‐transferase, in An. gambiae s.s. survivors exposed to permethrin in bottle bioassays compared with knocked down and unexposed individuals. No An. arabiensis showed elevated enzyme activity. The 1014S kdr allele was fixed in the Bungoma An. gambiae s.s. population and absent from An. arabiensis, whereas the 1014F kdr allele was absent from all samples of both species. Insecticide resistance could compromise vector control in Bungoma and could spread to other areas as coverage with longlasting insecticide‐treated bednets increases.     

Early biting rhythm in the Afro-tropical vector of malaria, Anopheles arabiensis, and challenges for its control in Ethiopia

The biting cycle of the malaria vector Anopheles arabiensis Patton (Diptera: Culicidae) was assessed by hourly light trap collections in three villages in Tigray, northern Ethiopia. Hourly catches were conducted in two houses in each village, for four consecutive nights. Light traps were set from 18.00 hours to 07.00 hours in houses in which people slept under untreated bednets. Anopheles arabiensis showed early biting activities, which peaked between 19.00 hours and 20.00 hours in the three villages; over 70% of biting activity occurred before 22.00 hours, when people typically retire to bed. This early biting activity may have a negative impact on the efficiency of bednets to control malaria.     

害虫遗传防治的研究历史与现状

作为防治或根除重大害虫最为有效的手段之一,害虫遗传防治在世界范围内被广泛采用并取得了巨大成功。本文综述了不育昆虫技术、雌性致死系统和昆虫显性致死技术等经典害虫遗传防治策略的发展历史、技术特点和应用情况。近年来,许多新的分子生物手段被不断提出并整合到害虫遗传防治策略中,包括归巢核酸内切酶基因、锌指核酸酶、转录激活因子样效应因子核酸酶、CRISPR/Cas9系统、Medea元件、Killer-Rescue系统、Wolbachia-细胞质不亲和性系统等。基于这些新的工具手段,许多国家已经在不同程度上启动了下一代害虫遗传防治项目。而我国在该领域的研究相对薄弱,需要在借鉴国外成功经验的同时,进一步加强害虫遗传防治的基础和应用研究,从而实现本地有害生物的可持续治理和外来入侵生物的有效狙击,确保我国未来的粮食和生态安全。     

不同饲养温度对橘小实蝇蛹色伴性遗传品系的影响

分别在19℃,22℃,25℃,28＇t2,31℃下饲养橘小实蝇蛹色伴性遗传品系,统计各温度下卵到蛹的的获得率、蛹重、羽化率、存活率及飞出率。结果表明卵到蛹的获得率28℃最大,为62．12％,19℃最小,为43．12％;蛹重25℃最重为1．3854g／100粒,19℃最轻,为1．2610g／100粒;羽化率25℃最高,为93％,31℃最低,仅82．67％;存活率31℃最高,为66％,19℃最低,仅为4．67％;飞出率25℃最高,为65％,31℃最低,为16％。综合不同温度下的卵到蛹的的获得率、蛹重、羽化率、存活率及飞出率得出25℃-28℃是大量饲养橘小实蝇蛹色伴性遗传品系的最佳温度。     

Floristic composition in relation to environmental gradients across KwaZulu‐Natal,South Africa

Conservation planning in the face of global change is still in its infancy. A suggested approach is to incorporate environmental gradients into conservation planning as they reflect the ecological and evolutionary processes generating and maintaining diversity. Our study provides a framework to identify the dominant environmental gradients determining floristic composition and pattern. Nonmetric multidimensional scaling was used on 2155 sampling plots in savanna and grassland habitat located across the province of KwaZulu‐Natal, South Africa (94 697 km²), a floristically rich region having steep environmental gradients, to determine the dominant gradients. Hierarchical cluster analysis was used to group similar plots which were then used in a Classification and Regression Tree analysis to determine the environmental delimiters of the identified vegetation clusters. Temperature‐related variables were the strongest delimiters of floristic composition across the province, in particular mean annual temperature. Frost duration was the primary variable in the Classification and Regression Tree analysis with important implications for savanna/grassland dynamics. Soil properties (base, pH status) and moisture variables accounted for most of the variation for the second and third axes of floristic variation. Given that climatic and edaphic variables were well correlated with floristic composition, it is anticipated that a changing climate will have a marked influence on floristic composition. We predict warmer temperatures may facilitate the spread of frost sensitive savanna species into previously cooler, grassland areas. Species associated with specific soil types will not easily be able to move up the altitudinal gradient to cooler climes because geology is aligned in an approximately north‐south direction compared with increasing altitude from east‐west. Future conservation planning should take cognisance of these gradients which are surrogates for ecological and evolutionary processes promoting persistence.     

Isolation and characterization of a manganese‐oxidizing bacterium from a biofiltration system for the treatment of borehole water in KwaZulu‐Natal (South Africa)

Using minimal salts medium containing vitamins and pyruvate (MSVP) plus added manganese sulfate, a manganese (II) oxidizing bacterial strain was isolated from water samples of a biofiltration system treating borehole water in KwaZulu‐Natal, South Africa. The nonmotile Gram‐negative and oxidase‐negative isolate was subsequently characterized microbiologically. Based on its morphological and physiological characteristics and on the analysis of its 16S rRNA gene sequence, the isolate was assigned to the genus Acinetobacter. Growth of the isolated strain in MSVP with added manganese sulfate gave rise to a drop in pH and a concomitant increase in oxidation–reduction potential, which was absent in controls, thus indicating manganese oxidation. The ability of Acinetobacter sp. strain LB1 to oxidize Mn (II) was further verified using the leucoberbelin blue dye assay as well as by energy dispersive X‐ray analysis of crystals formed in the medium. In addition, a biofilm assay indicated that this isolate can attach to solid surfaces such as a biofilter matrix, thus confirming its potential for biotechnological applications in the area of water purification.     

Female sterility in hybrids between Anopheles gambiae and A. arabiensis, and the causes of Haldane's rule

Although F1 female hybrids between Anopheles gambiae and A. arabiensis are fully fertile, sterility is present in backcross females. Here we report the results of a study into the genetic basis of backcross female sterility. Using 23 markers, we performed quantitative trait loci (QTL) mapping analyses to identify chromosomal regions involved in hybrid female sterility. We found that female sterility in backcrosses in both directions is primarily caused by interspecific interactions between a heterozygous X chromosome and recessive autosomal factors. In addition, our data provide support for two theories implicated in Haldane's rule in a single taxon. A comparison with data from a previous study shows that male hybrid sterility QTL are present in higher numbers than female hybrid sterility QTL. Furthermore, autosomal female sterility factors tend to be recessive, supporting the dominance theory for female sterility. Finally, our data indicate a very large effect of the X chromosome from both species on hybrid female sterility, despite the fact that the X chromosome represents less than 9% of the genome. However, this could be the result of a lack of introgression of the X chromosome between A. gambiae and A. arabiensis, rather than a faster evolution of sterility factors on the X chromosome.     

Efficacy of three insect repellents against the malaria vector Anopheles arabiensis

Three commercial repellents marketed in South Africa: Bio-Skincare (BSC, oils of coconut, jojoba, rapeseed and vitamin E), Mosiguard towelletes with 0.574 g quwenling (p-menthane-3,8-diol, PMD) and the standard deet (15% diethyl-3-methylbenzamide, Tabard lotion), were compared against a laboratory colony of the mosquito Anopheles arabiensis Patton (Diptera: Culicidae), the predominant malaria vector in South Africa. Human forearms were treated with 1.2 g BSC, 0.8 g PMD towelette or 0.5 g deet and exposed to 200 hungry An. arabiensis females for 1 min, at intervals of 1-6 h post-treatment. Tests were conducted by three adult male volunteers (aged 30-45 years, crossover controlled test design for 3 consecutive days), using their left arm for treatment and right arm for untreated control. Biting rates averaged 39-52 bites/min on untreated arms. All three repellents provided complete protection against An. arabiensis for up to 3-4 h post-application; deet and PMD gave 90-100% protection up to 5-6h, but BSC declined to only 52% protection 6h post-treatment. These results are interpreted to show that all three repellent products give satisfactory levels of personal protection against An. arabiensis for 4-5 h, justifying further evaluation in the field.     

Epigaeic ant diversity and distribution in the Sandstone Sourveld in KwaZulu‐Natal,South Africa

Ants are sensitive to habitat change and may be affected by disturbances, such as alien plant invasion. Alien plant invasion is associated with negative effects on the functioning of ecosystems and may have adverse impacts on biodiversity. The aim of this study was to determine the diversity of ground‐dwelling ants in Tanglewood and Giba Gorge Reserves in KwaZulu‐Natal Province, South Africa. Ants were sampled in the wet and dry seasons. Pitfall trap sampling was carried out in an intact grassland, forest and a disturbed grassland. We collected 360 samples resulting in a total of 2,577 occurrences comprising of 54 species. We found that diversity of ants in the two sites was influenced by vegetation type. The intact grassland in the two reserves had greater diversity (40 ± 4.45) of ants compared with forest (22 ± 4.86) and disturbed grassland (27 ± 1.15); however, the disturbed grassland supported higher ant occurrences (50.03 ± 31.6). Opportunists represented the most diverse functional group with 17 species followed by specialist predators with 13 species and generalised Myrmicinae with 10 species. These results suggest that grassland disturbance by alien plant invasion provides suitable environmental conditions that may increase ant occurrences but decrease ant diversity.     

Impact of insecticide-treated bed nets implementation on the genetic structure of Anopheles arabiensis in an area of irrigated rice fields in the Sahelian region of Cameroon

Variation at 12 microsatellite loci was investigated to assess the impact of the implementation of insecticide-treated bed nets (ITNs) on the genetic structure of Anopheles arabiensis in Simatou, a village surrounded by irrigated rice fields in the Sahelian area of Cameroon. The An. arabiensis population of Simatou was sampled twice before ITN implementation, and twice after. Effective population size estimates (N(e)) were similar across each time point, except for the period closely following ITN introduction where a nonsignificant reduction was recorded. Hence, we believe that ITN implementation resulted in a temporary bottleneck, rapidly followed by a demographic expansion. The genetic diversity of the population was not significantly affected since different genetic parameters (allele number, observed and expected heterozygosities) remained stable. Low estimates of genetic differentiation between the populations from Simatou and Lagdo, separated by 300 km, suggested extensive gene flow among populations of An. arabiensis in the Sahelian region of Cameroon. A decrease in the susceptibility to deltamethrin was observed following ITN introduction, but no kdr mutation was detected and a metabolic resistance mechanism is probably involved. The temporary effect of ITNs on the genetic structure of An. arabiensis population suggests that, to optimize the success of any control programme of this species based on ITNs, the control area should be very large and the programme should be implemented for a long period of time.     

Studies on the resting behaviour and host choice of Anopheles gambiae and An. arabiensis from Muleba,Tanzania

The relative efficacy of a mechanical (Prokopack) collection method vs. manual aspiration in the collection of resting mosquitoes was evaluated in northern Tanzania before and after an intervention using indoor residual spraying and longlasting insecticide‐treated nets. In smoke‐free houses mosquitoes were collected from the roof and walls, but in smoky houses mosquitoes were found predominantly on the walls. Anopheles gambiae (Diptera: Culicidae) constituted 97.7% of the 312 An. gambiae complex specimens identified before but only 19.3% of the 183 identified after the intervention. A single sampling with the Prokopack collected a third of the available insects. Anopheles gambiae completed its gonotrophic development indoors, whereas Anopheles arabiensis did so outdoors. In both species gonotrophic development took 2 days. Most unfed resting An. arabiensis collected outdoors were virgins, whereas the majority of engorged insects were parous (with well‐contracted sacs). Daily survival was estimated to be 80.0%. Only 9.4% of the engorged An. arabiensis collected outdoors and 47.1% of those collected indoors had fed on humans. Using the Prokopack sampler is more efficient than manual methods for the collection of resting mosquitoes. Malaria transmission may have been affected by a change in vector composition resulting from a change in feeding, rather than reduced survival. Monitoring the proportions of members of the An. gambiae complex may provide signals of an impending breakdown in control.