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Reliance on broad-spectrum insecticides and chemotherapeutic agents to control hematophagous insect vectors, and their related diseases is threatened by increasing insecticide and drug resistance, respectively. Thus, development of novel, alternative, complementary and effective technologies for surveillance and control of such insects is strongly encouraged. Semiochemicals are increasingly developed for monitoring and intervention of insect crop pests, but this has not been adequately addressed for hematophagous insects of medical and veterinary importance. This review provides an insight in the application of semiochemicals for control of hematophagous insects. Here, we provide specific information regarding the isolation and identification of semiochemical compounds, optimization approaches, detection, perception and discrimination by the insect olfactory system. Navigation of insects along wind-borne odor plumes is discussed and methods of odor application in field situations are reviewed. Finally, we discuss prospects and future challenges for the application of semiochemical-based tools with emphasis on mosquitoes. The acquired knowledge can guide development of more effective components of integrated vector management, safeguard against emerging resistance of insects to existing insecticides and reduce the burden of vector-borne diseases. [ABSTRACT FROM AUTHOR]

Vector‐borne diseases often originate from wildlife and can spill over into the human population. One of the most important determinants of vector‐borne disease transmission is the host preference of mosquitoes. Mosquitoes with a specialised host preference are guided by body odours to find their hosts in addition to carbon dioxide. Little is known about the role of mosquito host preference in the spillover of pathogenic agents from humans towards animals and vice versa. In the Republic of Congo, the attraction of mosquitoes to primate host odours was determined, as well as their possible role as malaria vectors, using odour‐baited traps mimicking the potential hosts of mosquitoes. Most of the mosquito species caught showed a generalistic host preference. Anopheles obscurus was the most abundant Anopheles mosquito, with a generalistic host preference observed from the olfactory response and the detection of various Plasmodium parasites. Interestingly, Culex decens showed a much higher attraction towards chimpanzee odours than to human or cow odours. Human Plasmodium parasites were observed in both human and chimpanzee blood, although not in the Anopheles mosquitoes that were collected. Understanding the role of mosquito host preference for cross‐species parasite transmission provides information that will help to determine the risk of spillover of vector‐borne diseases. [ABSTRACT FROM AUTHOR]

Culicoides species from the Obsoletus group are important vectors of bluetongue and Schmallenberg virus. This group consists of several species that cannot easily be identified using morphological characteristics. Therefore, limited information is available about their distribution and habitat preferences. In this study, we aimed to elucidate the species composition of the Obsoletus group in three habitat types at climatically different latitudes across Europe. Traps were placed in three habitat types in three countries at different latitudes. After DNA extraction, biting midges were identified using PCR and gel electrophoresis. Extraction of DNA using Chelex proved to be a cost and time efficient method for species identification. A latitudinal effect on the relative abundance of species from the Obsoletus group was found. Species composition was unique for most country‐habitat combinations. The majority of biting midges were either C. obsoletus s.s. or C. scoticus, and both species were found at all latitudes and habitats. Their wide distribution and their high abundance at livestock farms make these species likely candidates for rapid farm‐to‐farm transmission of pathogens throughout Europe. Our results emphasize the need to differentiate Obsoletus group species to better understand their ecology and contribution to pathogen transmission. [ABSTRACT FROM AUTHOR]

Background: Anopheles (An.) coluzzii, one of Africa's primary malaria vectors, is highly anthropophilic. This human host preference contributes greatly to its ability to transmit malaria. In contrast, the closely related An. quadriannulatus prefers to feed on bovids and is not thought to contribute to malaria transmission. The diverged preference for host odor profiles between these sibling species is likely reflected in chemosensory gene expression levels in the olfactory organs. Therefore, we compared the transcriptomes of the antennae and maxillary palps between An. coluzzii and An. quadriannulatus, focusing on the major chemosensory gene families. Results: While chemosensory gene expression is strongly correlated between the two species, various chemosensory genes show significantly enhanced expression in one of the species. In the antennae of An. coluzzii the expression of six olfactory receptors (Ors) and seven ionotropic receptors (Irs) is considerably enhanced, whereas 11 Ors and 3 Irs are upregulated in An. quadriannulatus. In the maxillary palps, leaving aside Irs with very low level of expression, one Ir is strongly enhanced in each species. In addition, we find divergence in odorant binding protein (Obp) gene expression, with several highly expressed Obps being enhanced in the antennae and palps of An. coluzzii. Finally, the expression of several gustatory receptors (Grs) in the palps appears to be species-specific, including a homolog of a sugar-sensing Drosophila Gr. Conclusions: A considerable number of Ors and Irs are differentially expressed between these two closely related species with diverging host preference. These chemosensory genes could play a role in the human host preference of the malaria vector An. coluzzii. Additionally, divergence in Obp expression between the two species suggests a possible role of these odor carrier proteins in determining host preference. Finally, divergence in chemosensory expression in the palps may point towards a possible role for the maxillary palps in host differentiation. [ABSTRACT FROM AUTHOR]

The host preferences of the anthropophilic mosquito species in the Anopheles gambiae complex (Diptera: Culicidae) are mediated by skin bacterial volatiles. However, it is not known whether these mosquitoes respond differentially to skin bacterial volatiles from non-human host species. In this study, the responses of two malaria mosquito species in the An. gambiae complex, Anopheles gambiae s.s. (hereafter, An. gambiae) and An opheles arabiensis, with different host preferences, to volatiles released from skin bacteria were tested. Skin bacteria collected from human, cow and chicken skin significantly increased trap catches; traps containing bacteria collected from human skin caught the highest proportions of An. gambiae and An. arabiensis. Traps with bacteria of human origin caught a significantly higher proportion of An. gambiae than of An. arabiensis, whereas bacterial volatiles from the chicken attracted significantly higher numbers of An. arabiensis than of An. gambiae. Additionally, An. gambiae showed a specialized response to volatiles from four specific bacteria, whereas An. arabiensis responded equally to all species of bacteria tested. Skin bacterial volatiles may therefore play important roles in guiding mosquitoes with different host preferences. The identification of these bacterial volatiles can contribute to the development of an odour blend that attracts mosquitoes with different host preferences. [ABSTRACT FROM AUTHOR]

Many haematophagous ectoparasites use carbon dioxide (CO2) and host odour to detect and locate their hosts. The tick Ixodes ricinus (Linnaeus) (Ixodida: Ixodidae) walks only small distances and quests in vegetation until it encounters a host. The differential effects of CO2 and host odour on the host-finding behaviour of I. ricinus have, however, never been clarified and hence represent the subject of this study. The effects of CO2 and odour from bank voles on the activation and attraction of I. ricinus nymphs were analysed in a Y-tube olfactometer. Carbon dioxide evoked a response in the absence and presence of host odour, but did not attract nymphs. Host odour, however, did not evoke a response but did attract nymphs in the absence and presence of CO2. The current results show that CO2 is an activator, but not an attractant, and that host odour is an attractant, but not an activator, of I. ricinus nymphs, and provide ecological insights into the host-finding behaviour of I. ricinus. [ABSTRACT FROM AUTHOR]

Understanding the impact of altitude and ecological heterogeneity at a fine scale on the populations of malaria vectors is essential to better understand and anticipate eventual epidemiological changes. It could help to evaluate the spread of alleles conferring resistance to insecticides and also determine any increased entomological risk of transmission in highlands due to global warming. We used microsatellite markers to measure the effect of altitude and distance on the population genetic structure of Anopheles funestus and Anopheles gambiae s.s. in the Muheza area in the north-eastern part of Tanzania (seven loci for each species). Our analysis reveals strong gene flow between the different populations of An. funestus from lowland and highland areas, as well as between populations of An. gambiae sampled in the lowland area. These results highlight for An. funestus the absence of a significant spatial subpopulation structuring at small-scale, despite a steep ecological and altitudinal cline. Our findings are important in the understanding of the possible spread of alleles conferring insecticide resistance through mosquito populations. Such information is essential for vector control programmes to avoid the rapid spread and fixation of resistance in mosquito populations. [ABSTRACT FROM AUTHOR]

Mosquito repellents are used around the globe to protect against nuisance biting and disease-transmitting mosquitoes. Recently, there has been renewed interest in the development of repellents as tools to control the transmission of mosquito-borne diseases. We present a new bioassay for the accurate assessment of candidate repellent compounds, using a synthetic odour that mimics the odour blend released by human skin. Using DEET ( N, N-diethyl-meta-toluamide) and PMD ( p-menthane-3,8-diol) as reference compounds, nine candidate repellents were tested, of which five showed significant repellency to the malaria mosquito Anopheles gambiae sensu stricto (Diptera: Culicidae). These included: 2-nonanone; 6-methyl-5-hepten-2-one; linalool; δ-decalactone, and δ-undecalactone. The lactones were also tested on the yellow fever mosquito Aedes aegypti ( Stegomyia aegypti) (Diptera: Culicidae), against which they showed similar degrees of repellency. We conclude that the lactones are highly promising repellents, particularly because these compounds are pleasant-smelling, natural products that are also present in human food sources. [ABSTRACT FROM AUTHOR]

The insect endosymbiont Wolbachia pipientis (Rickettsiales: Rickettsiaceae) is undergoing field trials around the world to determine if it can reduce transmission of dengue virus from the mosquito Stegomyia aegypti to humans. Two different Wolbachia strains have been released to date. The primary effect of the wMel strain is pathogen protection whereby infection with the symbiont limits replication of dengue virus inside the mosquito. A second strain, wMelPop, induces pathogen protection, reduces the adult mosquito lifespan and decreases blood feeding success in mosquitoes after 15 days of age. Here we test whether Wolbachia infection affects mosquito attraction to host odours in adults aged 5 and 15 days. We found no evidence of reduced odour attraction of mosquitoes, even for those infected with the more virulent wMelPop. This bodes well for fitness and competitiveness in the field given that the mosquitoes must find hosts to reproduce for the biocontrol method to succeed. [ABSTRACT FROM AUTHOR]

A strategy to decrease the vector competence of Anopheles gambiae sensu stricto (Diptera: Culicidae), the most efficient malaria vector in Africa, may consist of exploiting the genes involved in zoophily. Crossing and backcrossing experiments were performed between An. gambiae s.s. and the zoophilic sibling species Anopheles quadriannulatus. Mosquito strains were tested in a dual-choice olfactometer to investigate their responses to cow odour. Totals of 12% of An. gambiae s.s. and 59% of An. quadriannulatus selected the port with the cow odour. Crosses and backcrosses did not show a significant preference for the cow-baited port. The results indicated that anthropophilic behaviour in An. gambiae s.s. is a dominant or partially dominant trait, which, in conjunction with the unstable zoophilic behaviour observed in An. quadriannulatus, poses a serious obstacle to plans to decrease vector competence by modifying the anthropophilic trait. [ABSTRACT FROM AUTHOR]

Summary Q fever has emerged as an important human and veterinary public health problem in the Netherlands with major outbreaks in three consecutive years. Goat farms are probably the prime source from which Coxiella burnetii have spread throughout the environment, infecting people living in the vicinity. Coxiella burnetii infection not only spilled over from animal husbandry to humans but could also have spread to neighbouring wildlife and pets forming novel reservoirs and consequently posing another and lingering threat to humans, companion animals and livestock. In these cases, transmission routes other than airborne spread of contaminated aerosols may become significant. Therefore, the role of ticks in the transmission of Coxiella burnetii in the current situation was investigated. A total of 1891 questing Ixodes ricinus ticks and 1086 ticks feeding on pets, wildlife and livestock were tested by a recently developed multiplex Q-PCR. All ticks were negative, except for a few ticks feeding on a herd of recently vaccinated sheep. Coxiella-positive ticks were not detected after resampling this particular herd three months later. Based on these data we conclude that the current risk of acquiring Q fever from questing ticks in the Netherlands is negligible. However, for future risk assessments, it might be relevant to sample more ticks in the vicinity of previously C. burnetii infected goat farms and to assess whether C. burnetii can be transmitted transovarially and transstadially in I. ricinus ticks. [ABSTRACT FROM AUTHOR]

The main objective was to investigate malaria transmission dynamics in three different sites, two highland villages (Fort Ternan and Lunyerere) and a lowland peri-urban area (Nyalenda) of Kisumu city. Adult mosquitoes were collected using PSC and CDC light trap while malaria parasite incidence data was collected from a cohort of children on monthly basis. Rainfall, humidity and temperature data were collected by automated weather stations. Negative binomial and Poisson generalized additive models were used to examine the risk of being infected, as well as the association with the weather variables. Anopheles gambiae s.s. was most abundant in Lunyerere, An. arabiensis in Nyalenda and An. funestus in Fort Ternan. The CDC light traps caught a higher proportion of mosquitoes (52.3%) than PSC (47.7%), although not significantly different (P = 0.689). The EIR's were 0, 61.79 and 6.91 bites/person/year for Fort Ternan, Lunyerere and Nyalenda. Site, month and core body temperature were all associated with the risk of having malaria parasites (P < 0.0001). Rainfall was found to be significantly associated with the occurrence of P. falciparum malaria parasites, but not relative humidity and air temperature. The presence of malaria parasite-infected children in all the study sites provides evidence of local malaria transmission. [ABSTRACT FROM AUTHOR]

Host-seeking behaviour of the anthropophilic malaria vector Anopheles gambiae sensu stricto (Diptera: Culicidae) is mediated predominantly by olfactory cues. Several hundreds of odour components have been identified from human emanations, but only a few have been proven to act as attractants or synergists in the host-seeking behaviour of female An. gambiae. In previous work, aromatics, alcohols and ketones in human odours were found to elicit electrophysiological activity in antennal olfactory neurons of female An. gambiae. However, the behavioural effects of these compounds have not been investigated. In this study, behavioural responses of female An. gambiae to components of human breath, urine and sweat at a series of concentrations, or a single concentration in the case of acetone, were examined in combination with ammonia and L-lactic acid in a dual-choice olfactometer. The results showed that at specific concentrations 4-ethylphenol, indole, 3-methyl-1-butanol and two ketones inhibited the attractive effect of a mixture of ammonia and lactic acid. Acetone on its own was not attractive; however, when combined with lactic acid, the binary mixture was attractive. When combined with ammonia, acetone inhibited the attractiveness exerted by ammonia alone. Dodecanol and dimethyldisulphide did not affect the attraction exerted by ammonia and lactic acid at any of the concentrations tested. By contrast, a human-specific armpit odour, 7-octenoic acid, augmented the attraction exerted by the combination of ammonia and lactic acid at a specific dosage. [ABSTRACT FROM AUTHOR]

In the summer of 2005, the Asian tiger mosquito, Aedes albopictus (Skuse) (Diptera: Culicidae) was found for the first time in the Netherlands. It was collected on the premises of several horticultural companies that import the ornamental plant Dracaena sanderiana (Sparagalus: Dracaenaceae [Agavaceae]), known as Lucky bamboo, from southern China, an area endemic for this mosquito species and for arboviruses transmitted by this vector. Here we report the results of a 1-year survey of the distribution and vector status of Ae. albopictus in Lucky bamboo nurseries in the Netherlands (July 2006–June 2007). As it had been established previously that the presence of this species was linked to the import of Lucky bamboo, the survey was conducted only on sites owned by relevant import companies. In total, 569 adult Ae. albopictus were collected with mosquito traps from 15 of the 17 (88%) glasshouses used by Lucky bamboo importers, none of which were found to be infected with dengue virus. On two occasions there was evidence that Ae. albopictus had escaped from the glasshouses, but, overall, there was no evidence that a population had become established in the greenhouses or elsewhere. [ABSTRACT FROM AUTHOR]

The article presents a study on the daily temperature dynamics of malaria mosquito breeding sites and on the relationships between meteorological variables and water temperature in western Kenya. It states that besides affecting the mosquito immatures directly, water temperature will have an impact on the diversity, densities and activity of other aquatic organisms, including possible predators, pathogens and food resources, such as algal matter, of the mosquito larvae. It mentions that this study demonstrated that there were strong and significant correlations between the average water temperature and various meteorological variables, including the average air temperature.

Differences between human individuals in their attractiveness to female mosquitoes have been reported repeatedly, but the underlying mechanisms are not well understood. Skin emanations from 27 human individuals, collected on glass marbles, were tested against ammonia in a dual-choice olfactometer to establish their degrees of attractiveness to anthropophilic Anopheles gambiae s.s. Giles (Diptera: Culicidae) mosquitoes. Ammonia was used as a standard odour source because of its proven attractiveness to An. gambiae s.s. Skin emanations from most volunteers attracted significantly more mosquitoes than ammonia. There were clear differences in the attractiveness of skin emanations from different volunteers relative to that of ammonia, as well as in the strength of the trap entry response. Consistent differences were observed when emanations from the three most and the three least attractive volunteers were tested pairwise. No gender or age effect was found for relative attractiveness or trap entry response. Emanations from volunteers with higher behavioural attractiveness elicited higher electroantennogram response amplitudes in two pairs, but in a third pair a higher electroantennogram response was found for the less attractive volunteer. These results confirm that odour contributes to the differences in attractiveness of humans to mosquitoes. [ABSTRACT FROM AUTHOR]

Several highland areas in eastern Africa have recently suffered from serious malaria epidemics. Some models predict that, in the short term, these areas will experience more epidemics as a result of global warming. However, the various processes underlying these changes are poorly understood. We therefore investigated malaria prevalence, malaria vector densities and malaria vector survival in a highland area in western Kenya, ranging from approximately 1550–1650 m altitude. Although only five adult malaria vectors were collected during 180 light traps and 180 resting collections over a 23-month study period, malaria was prevalent among school children (average parasite prevalence: 10%). During an extensive survey of potential larval habitats, we identified only seven habitats containing Anopheles gambiae Giles s.l. larvae. Their limited number and low larval densities suggested that their contribution to the adult vector population was small. Experiments on adult and larval survival showed that at this altitude, adult mosquitoes survived inside local houses, but that larval development was severely retarded: only 2 of 500 A. gambiae s.l. larvae developed to the pupal stage, whereas all other larvae died prior to pupation. At present, high vector densities are unlikely because of unfavourable abiotic conditions in the area. However, temporary favourable conditions, such as during El Niño years, may increase larval vector survival and may lead to malaria epidemics. [ABSTRACT FROM AUTHOR]

The host preference ofAnopheles quadriannulatusTheobald (Diptera: Culicidae), the zoophilic member of the malaria mosquito complexAnopheles gambiaeGiles, was investigated in a dual-choice olfactometer. Naïve female mosquitoes were exposed to CO2, acetone, 1-octen-3-ol, and skin emanations from cows and humans in various combinations. Their behavioural responses were recorded when they had entered one of either upwind traps from where the odours were being released. The mosquitoes did not respond to CO2 when released at human or cattle equivalent concentrations. Too few mosquitoes responded to acetone to allow for a statistical analysis. The combination of CO2+ 1-octen-3-ol was repellent. Cow odour alone was slightly attractive, but there was a synergistic attractive effect of cow odour+ CO2. Surprisingly, the mosquitoes were attracted to human odour, and in a choice situation human odour was selected above cow odour+ CO2. AnthropophilicAn. gambiaeGiles s.s. was repelled by cow odour+ CO2 in contrast toAn. quadriannulatus. In a choice situation, both mosquito species selected human odour above cow odour+ CO2. The implications of these results are discussed in the light of recent behavioural data from the field. [ABSTRACT FROM AUTHOR]

Behavioural and electrophysiological responses ofAnopheles gambiaeGilessensustricto (Diptera: Culicidae) to human skin emanations collected on glass beads were studied using a dual-port olfactometer and electroantannography. Glass beads to which skin emanations from human hands had been transferred elicited a level of attraction similar to a human hand. The attractiveness of these handled glass beads faded away 4 h after transfer onto the beads. Storage at−20°C for up to 8 weeks showed a decreased but still attractive effect of the beads. In a choice test between one individual and four others, the emanations from the reference individual were significantly more attractive in three out of four cases. The headspace of handled glass beads elicited a dose-dependent EAG response. The substances causing EAG activity could be removed partially by dichloromethane, ethanol and pentane-ether. Glass beads provide a suitable neutral substrate for the transfer of human odour to enable chemical analysis of the human skin emanations for identification of kairomones of anthropophilic mosquitoes. [ABSTRACT FROM AUTHOR]

Competitive interactions among the aquatic stages of the malaria mosquito Anopheles gambiae s.l. (Diptera: Culicidae) may affect the resulting adult densities and, hence, the risk of malaria. We investigated the impact of the presence of a fourth-instar larva ( An. gambiae Giles s.s. or An. arabiensis Patton), the quantity of food, and the available space on the survival and development of freshly hatched larvae of An. gambiae s.s. and An. arabiensis. To analyse the results, two proportional hazard models were constructed. The first estimated the effects of all covariates on mortality rate and the second estimated the effects of the covariates on development rate into the third larval instar (L3). A time-dependent covariate for density, which changed during the experiment as a result of death or development to L3, was included in both models. In the presence of a fourth-instar larva (L4), survival of the experimental larvae was significantly reduced, but no difference was detected between the presence of L4 An. gambiae and L4 An. arabiensis. The observation that the majority of dead larvae were not recovered in trays with an L4 present suggested that cannibalism and predation occurred readily. Limitation in space significantly increased mortality of larvae, whereas a limitation of food reduced larval development rate, but did not cause mortality per se. From this, we concluded that both cannibalism and predation were enhanced as a result of more frequent interactions within smaller environments, but did not occur for reasons of food shortage. This study shows that inter- and intraspecific interactions among larvae of the An. gambiae complex strongly affect survival and development, and that the quantity of food and the available space are important determinants of the outcome of these interactions. Implications of the results are discussed with respect to the population dynamics of both malaria vectors in the field. [ABSTRACT FROM AUTHOR]

Abstract. Among the aquatic developmental stages of the Anopheles gambiae complex (Diptera: Culicidae), both inter- and intra-specific interactions influence the resulting densities of adult mosquito populations. For three members of the complex, An. arabiensis Patton, An. quadriannulatus (Theobald) and An. gambiae Giles sensu stricto , we investigated some aspects of this competition under laboratory conditions. First-instar larvae were consumed by fourth-instar larvae of the same species (cannibalism) and by fourth-instar larvae of other sibling species (predation). Even when larvae were not consumed, the presence of one fourth-instar larva caused a significant reduction in development rate of first-instar larvae. Possible implications of these effects for population dynamics of these malaria vector mosquitoes are discussed. [ABSTRACT FROM AUTHOR]

A field study was carried out in the rice irrigation scheme Office du Niger, Mali, to observe malaria mosquito larval development as related to differences in field irrigation practices, such as water level, irrigation application and irrigation frequency. The main aim was to find out to what extent field water management can be considered as a tool for vector control for this irrigation system. The results show that minor differences in water management do result in small differences in mosquito development, with respect to larval densities and species composition. The main malaria vector for the area, An. gambiae s.l., developed predominantly in the first six weeks after transplanting. Due to improper drainage after harvest An. gambiae s.l. breeding quickly re-established on fields where small water pools remained. Although further research is needed, suggestions for mosquito control in the Office du Niger would be a strict performance of the agricultural calendar in combination with a rotation of transplanting in large blocks. [ABSTRACT FROM AUTHOR]

Abstract. The strongly anthropophilic behaviour of Anopheles gambiae Giles sensu stricto (Diptera: Culicidae), the most important malaria vector in Africa, has been demonstrated by field and laboratory studies. Other members of the An. gambiae complex express varied degrees of anthropophily. Anopheles quadriannulatus (Theobald) species A and B are more zoophilic members of the complex and hence are considered to be of no medical importance. Olfactometer experiments with An. quadriannulatus species A have demonstrated attraction to both human and cow odour. To extend these olfactometer observations a choice experiment was conducted in an outdoor cage with a human and a calf as baits, using laboratory-reared mosquitoes. Anopheles gambiae s.s. (from Liberia) and two strains of An. quadriannulatus species A (SKUQUA from South Africa, SANGQUA from Zimbabwe), marked with different coloured fluorescent powders for identification purposes, were released simultaneously and given an equal opportunity to feed on either host. The experiment was repeated six times. Bloodmeals were identified using the precipitin technique. Anopheles gambiae s.s. showed highly anthropophagic behaviour, taking 88% of bloodmeals from the human host. In contrast, both strains of An. quadriannulatus fed with equal frequency on the human or the calf; the response to either host was not significantly different. These results confirm the olfactometer findings and demonstrate anthropophagic behaviour not previously recorded in this species. This finding has implications for prospective manipulation of host preference for genetic control purposes. [ABSTRACT FROM AUTHOR]

Summary In an olfactometer study on the response of the anthropophilic malaria mosquito Anopheles gambiae s.s. (Diptera, Culicidae) to human sweat it was found that freshly collected sweat, mostly of eccrine origin, was attractive, but that incubated sweat was significantly more attractive than fresh sweat. The behavioural response to l-lactic acid and ammonia, the main constituents of sweat, was investigated. l-lactic acid was attractive at one concentration only (11.11 mm) and removal of the l-lactic acid from the sweat by enzymatic decomposition did not affect the attractiveness of sweat. Ammonia caused attraction over a range of 0.1–13.4 m on glass slides and at 0.84–8.40 μmol/min in an air stream. It is concluded that: human sweat contains kairomones for host-seeking An. gambiae; ammonia is an important kairomone for this mosquito; and that l-lactic acid is not a prerequisite in the attraction of An. gambiae to sweat. [ABSTRACT FROM AUTHOR]

SummaryFor collecting mosquitoes (Diptera: Culicidae) the outdoor catching efficiency of four types of trapping devices baited with carbon dioxide (CO2, 300 ml/min) was evaluated and compared in two areas of Tanzania. The types of traps employed were: the CDC miniature trap with the incandescent light bulb switched on or off; electric nets (ENT) and a Counterflow Geometry (CFG) trap. In Njage, south-east Tanzania, Anopheles gambiae Giles sensu stricto was the most abundant of the seven mosquito species obtained, comprising of 74.3% of the total number caught (n = 2171). In Muheza, north-east Tanzania, Culex quinquefasciatus Say was the predominant species (90.9%) among 1080 caught. At both localities the CFG trap was superior to the CDC trap with light-on or light-off for sampling both An. gambiae and Cx. quinquefasciatus. Efficiency of the CFG trap and ENT were similar for sampling these species of mosquitoes (P > 0.05). However, ENT was superior to the CDC trap with light-off for collecting both species. Significantly more (P < 0.05) Cx. quinquefasciatus were obtained by the CDC trap with light-off than with light-on, especially outdoors. It is concluded that both ENT and the CFG are effective tools for sampling populations of An. gambiae and Cx. quinquefasciatus outdoors. [ABSTRACT FROM AUTHOR]

Summary Mosquito larvae of the sibling species Anopheles arabiensis Patton and An. gambiae Giles sensu stricto (Diptera: Culicidae) were investigated for interspecific competition. Single-species and mixed-species populations were reared at 27°C from the first instar to pupation at different densities (100, 200 or 400 larvae/200 cm2 tray) with a constant amount of food, 0.2 mg/larva/day. Pupae obtained from mixed populations were identified to species using PCR. Both species had a 1 : 1 sex ratio at pupation. Development time to pupation averaged about one day less for An. arabiensis compared to An. gambiae, ranging from 0.93–1.49 d for males and from 0.44–0.84 d for females in single populations. In mixed species populations the difference for males ranged from 0.99–1.58 d and for females from 0.93–1.62 d. Survival rates of An. gambiae s.s. were significantly higher than those of An. arabiensis in both the single-species and mixed-species populations. Mixed-species rearing did not have an effect on the survival of An. gambiae, whereas the mortality rate of An. arabiensis was significantly higher in mixed populations than when only this species was reared at the same densities, suggesting a competitive disadvantage for An. arabiensis in mixed populations. High proportions of larvae (4–35%) were lost during development; these losses could not be accounted for by corpses found in the rearing pans. The possibility of cannibalism was investigated by rearing each species separately in small containers (five per 50 ml), inspected every 6 h, but no cannibalism was detected at any stage of development in either species. It was concluded that, under these experimental circumstances, interspecific competition between both species did occur but with a detrimental effect on An. arabiensis only. Relevance of these findings to the ecology of both species in the field is discussed briefly. [ABSTRACT FROM AUTHOR]

Studies on the behavioral and oviposition responses of Culex quinquefasciatus to 3-methylindole or skatole (an oviposition site cue) and (5 R,6 S)-6-acetoxy-5-hexadecanolide (the synthetic oviposition pheromone, SOP) were conducted in Muheza, northeast Tanzania. Cx. quinquefasciatus displayed a bimodal pattern of oviposition. The highest peak (64.8%) was between 18:00 and 20:00 hr, while the second peak (18.9%) was between 06:00 and 08:00 hr. The mean number of egg rafts oviposited per day between the two peaks was different ( P < 0.05). Oviposition responses of gravid Cx. quinquefasciatus differed across the range of concentrations of skatole. Larger numbers of egg rafts were deposited in bowls treated with 10−6 μg or 10−5 μg skatole than in bowls with tap water ( P < 0.05). The number of egg rafts deposited in bowls treated with 10−4 or 10−1 μg skatole was not different from that laid in tap water ( P > 0.05). Under field conditions skatole was found to be effective for a period of seven days, after which its biological activity decreased significantly. It was further found that more egg rafts of Cx. quinquefasciatus were deposited in water treated with SOP than in water treated with skatole ( P = 0.0002). An additive effect was observed when the SOP + skatole combination was used to attract gravid Cx. quinquefasciatus to oviposition sites. It is concluded that skatole and SOP mediate oviposition site selection of Cx. quinquefasciatus under field conditions. [ABSTRACT FROM AUTHOR]

Borrelia miyamotoi is a tick-borne bacterium that may cause relapsing fever in humans. As this pathogen has been discovered in Europe only recently, only little is known about its local impact on human health and its spatial distribution. In this study, we show the results of PCR screenings for B. miyamotoi in flagged Ixodes ricinus from Belgium and the Netherlands. B. miyamotoi was detected in nine of thirteen, and three of five locations from the Netherlands and Belgium, respectively. These outcomes indicate that B. miyamotoi is more spread than previously thought. The mean infection rate B. miyamotoi was 1.14% for Belgium and 3.84% for the Netherlands [ABSTRACT FROM AUTHOR]

The response of Culex mosquitoes to (5 R,6 S)-6-acetoxy-5-hexadecanolide (the synthetic oviposition pheromone, SOP), emanations from soakage pit water (SPW), and grass infusions (GI) was studied in pit latrines in Muheza, Tanzania. Water treated with the synthetic oviposition pheromone received more egg rafts of Culex quinquefasciatus Say and Cx. cinereus Theobald than did the untreated water ( P < 0.001). The residual activity of SOP did not decrease over a nine-day period, with the geometric mean number of egg rafts laid in the SOP-treated water varying daily between 2.5 and 8.9 as compared to 0.1–1.6 egg rafts laid in tap water. However, SOP did not attract ovipositing mosquitoes to nonbreeding sites, and both treatment and control received few eggs. SPW and GI attracted ovipositing Cx. quinquefasciatus, Cx. cinereus, and Cx. tigripes Grandpré and de Charmoy with the number of eggs rafts deposited in bowls containing SPW or GI being larger than that deposited in bowls with tap water ( P < 0.05). More egg rafts of Cx. quinquefasciatus were deposited in SOP-treated water than in SPW ( P < 0.05). When SOP was compared with SOP + SPW, more egg rafts of Cx. quinquefasciatus were deposited in bowls with the latter combination than in bowls containing SOP or SPW only ( P < 0.05), indicating a synergistic effect between SOP and SPW. Similarly, when SOP-treated water and GI were compared with SOP + GI, more egg rafts of Cx. quinquefasciatus were laid in the latter bowl, indicating a synergistic effect between SOP and GI. The result suggest that the combined use of SOP and organically enriched water can be employed in monitoring of Cx. quinquefasciatus for control programs. This is the first record of the attraction of Cx. cinereus and Cx. tigripes to oviposition stimuli. [ABSTRACT FROM AUTHOR]

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. The influence of adult body size on the pre-gravid state and fecundity was studied in Anopheles gambiae Giles females hand-caught inside houses and virgin females collected as pupae in Tanzania. Blood-fed mosquitoes were kept for 2-3 days before dissection and examination for insemination and ovarian condition. Those females which did not develop eggs were classified as pre-gravid. The number of mature eggs in those mosquitoes which became gravid was counted. Virgin females were fed and kept for egg maturation in the laboratory. Wing-length of females was measured as an index of mosquito size. The overall pre-gravid rate in the resting An. gambiae population was found to be 21% and, of these, 66% had been inseminated. In the virgin females the pre-gravid rate was 92.6%. The mean wing-length of wild females which became gravid was significantly larger than those which remained pre-gravid. There was a positive correlation between fecundity and wing-length. Smaller females tended to require two or three bloodmeals to facilitate completion of the first gonotrophic cycle. The critical size permitting oviposition from the first blood-meal was a wing-length of 3 mm. [ABSTRACT FROM AUTHOR]

. Various combinations of six candidate attractants -butanone, carbon dioxide (CO2), honey, octenol, lactic acid and mixed phenols - were tested against natural populations of mosquitoes in Everglades National Park, Florida, U.S.A., using unlighted CDC-baited traps. With few exceptions, the attractancy of these candidate compounds to mosquitoes, when used alone, was less than that of CO2 alone. The exceptions were that octenol and honey extract alone attracted larger numbers of Coquillettidiaperturbans (Walker). Addition of lactic acid and/or octenol to CO2 increased trap collections of Aedes taeniorhynchus (Wiedemann), Anopheles atropos D. & K., and An. crucians Wiedemann by 1.4-13.8 times. Culex nigripalpus Theobald collections were increased 2.7 times by the addition of lactic acid, while the addition of octenol produced mixed results. Whereas the addition of lactic acid reduced collections of Cx (Melanoconion) spp., the addition of octenol generally increased collections. The opposite happened for Wyeomyia mitchellii (Theobald). For the biting midge, Culicoides furens (Poey), octenol (1.6-23.4X) and phenol (2.7x) alone attracted larger numbers, and lactic acid alone attracted approximately the same numbers as CO2 alone. The combinations octenol + phenol and octenol + 200 ml/min CO2 increased C.furens collections c. 100 times over CO1 alone. The combination of octenol + CO2 increased (1.6x) collections of the tabanid Diachlorus ferrugatus (Fabricius). Butanone appeared to decrease the trap collections of all species when combined with CO2 or octenol + CO2. [ABSTRACT FROM AUTHOR]

The flight behavior of Anopheles gambiae s.s. Giles and An. stephensi Patton exposed to different odor cues was studied in a wind tunnel. Odors consisted of CO2, CO2 + acetone (at two concentrations), and CO2 + 1-octen-3-ol. Mosquitoes were released singly and their behavior was recorded on video. Parameters studied included flight velocity, percentage of time spent flying, percentage of time spent in plume, and number of turns toward the plume. Large differences in behavior toward the odors tested were observed. An. gambiae did not respond well to CO 2, whereas An. stephansi was positively affected by this compound. In contrast, An. gambiae responded significantly to CO 2 + acetone (at a low concentration), but the behavior of An. stephensi was completely suppressed by this combination of odor stimuli. CO 2 + a high concentration of acetone or CO 2 + 1-octen-3-ol did not cause significant effects in An. gambiae compared to no odor, while these treatments elicited strong behavioral responses in An. stephensi. The latter species responded particularly well to CO 2 + 1-octen-3-ol. The results suggest that the observed differences may be inherent to the known differences in host preferences, where An. gambiae is highly anthropophilic and An. stephensi more zoophilic. This would explain why the latter species responds well to CO 2 and even better to CO 2 + 1-octen-3-ol, a compound readily emitted by bovine ruminants. [ABSTRACT FROM AUTHOR]

Mosquitoes infected with malaria parasites have demonstrated altered behaviour that may increase the probability of parasite transmission. Here, we examine the responses of the olfactory system in Plasmodium falciparum infected Anopheles gambiae, Plasmodium berghei infected Anopheles stephensi, and P. berghei infected An. gambiae. Infected and uninfected mosquitoes showed differential responses to compounds in human odour using electroantennography coupled with gas chromatography (GC-EAG), with 16 peaks triggering responses only in malaria-infected mosquitoes (at oocyst, sporozoite or both stages). A selection of key compounds were examined with EAG, and responses showed differences in the detection thresholds of infected and uninfected mosquitoes to compounds including lactic acid, tetradecanoic acid and benzothiazole, suggesting that the changes in sensitivity may be the reason for differential attraction and biting at the oocyst and sporozoite stages. Importantly, the different cross-species comparisons showed varying sensitivities to compounds, with P. falciparum infected An. gambiae differing from P. berghei infected An. stephensi, and P. berghei infected An. gambiae more similar to the P. berghei infected An. stephensi. These differences in sensitivity may reflect long-standing evolutionary relationships between specific Plasmodium and Anopheles species combinations. This highlights the importance of examining different species interactions in depth to fully understand the impact of malaria infection on mosquito olfactory behaviour. [ABSTRACT FROM AUTHOR]