Comparison of carbon dioxide-baited trapping systems for sampling outdoor mosquito populations in Tanzania

A comparison of BG Sentinel and CDC trap attractants for mosquito surveillance in urban and suburban areas of Montgomery and Prince George's Counties, Maryland, U.S.A

Monitoring mosquito populations is crucial for vector-borne disease surveillance. Routine mosquito surveillance in many regions of the United States is performed either by vector abatement districts or public health departments. These surveillance programs often use multiple trap types and attractants to target key mosquito species, however setting different traps with varying attractants can be expensive and labor intensive. Because funding for mosquito control is highly variable throughout the U.S., some programs may be limited in their surveillance capabilities. To determine whether a single trap-attractant combination could provide specificity for key vector and nuisance species, as well as sensitivity for rare species, we compared the BG-Sentinel 2 and CDC miniature light traps paired with CO₂, UV-LED, BG Lure, BG Sweetscent, octenol, or chicken feathers. Trapping was conducted biweekly from June/July-October 2019 and 2020 in Montgomery and Prince George's County, MD. BG traps collected significantly more Aedes albopictus than CDC traps when paired with BG Lure, Sweetscent, or octenol. BG/CO₂ traps collected both the greatest number of total mosquitoes and Culex pipiens. BG/CO₂, CDC/CO₂, and CDC/UV traps provided the most diverse collections. Trapping with the CO₂-baited BG-Sentinel is recommended as an effective strategy for general mosquito surveillance when resources are limited.

Effect of Incandescent Light on Collection of West Nile Virus Vectors Using CDC Miniature Light Traps in Northern Colorado

To evaluate whether the presence of clear incandescent light was attractive or refractive to host-seeking mosquitoes in northern Colorado, a Bayesian hierarchical model was created to measure differences in trap effectiveness based on presence or absence of phototactic cues. A total of eight CDC miniature light traps (with and without light) were set weekly across four locations in northern Colorado between Weeks 23 and 32 of year 2020. Culex mosquitoes (Diptera: Culicidae) accounted for 81% of all collections in this study with two vectors of West Nile virus being represented. The probability of catching both Culex tarsalis Coquillett and Culex pipiens Linnaeus was reduced when traps were equipped with light, but the difference was not statistically significant for Culex tarsalis. The clear reduction in the number of Culex pipiens caught when these traps were equipped with light indicates negative phototactic behavior and underestimation with current surveillance strategies. Removal of light from these traps may aid our understanding of these species' distribution within the environment, improve collection efficiency, and help guide implementation of targeted control measures used in public health mosquito control.

Olfaction in Anopheles mosquitoes

As vectors of disease, mosquitoes are a global threat to human health. The Anopheles mosquito is the deadliest mosquito species as the insect vector of the malaria-causing parasite, which kills hundreds of thousands every year. These mosquitoes are reliant on their sense of smell (olfaction) to guide most of their behaviors, and a better understanding of Anopheles olfaction identifies opportunities for reducing the spread of malaria. This review takes a detailed look at Anopheles olfaction. We explore a range of topics from chemosensory receptors, olfactory neurons, and sensory appendages to behaviors guided by olfaction (including host-seeking, foraging, oviposition, and mating), to vector management strategies that target mosquito olfaction. We identify many research areas that remain to be addressed.

Impacts of ivermectin mass drug administration for onchocerciasis on mosquito populations of Ogun state, Nigeria

BACKGROUND

The impact of single-dose mass drug administration (MDA) of ivermectin for onchocerciasis on mosquito populations was investigated in Ogun State, Nigeria.

METHODS

Indoor and outdoor collection of mosquitoes was carried out in two intervention (IC) and two control communities (CC) at three different periods: pre-MDA (baseline), 2-3 days after MDA and 13-14 days after MDA. The density and parity rate of female Anopheles and Culex mosquitoes were determined and compared. Environmental and climatic data of study locations were obtained to perform generalized linear model analysis.

RESULTS

A total of 1399 female mosquitoes were collected, including 1227 Anopheles and 172 Culex mosquitoes. There was a similar magnitude of reduction in the indoor density of Anopheles by 29% in the IC and CC 2-3 days post-MDA but the reduction in indoor parity rate was significantly higher (p = 0.021) in the IC, reducing by more than 50%. In the IC, observation of a significant reduction at 2-3 days post-MDA was consistent for both the indoor density (1.43 to 1.02) and indoor parity rate (95.35% to 44.26%) of Anopheles mosquitoes. The indoor parity rate of Anopheles remained significantly reduced (75.86%) 13-14 post-MDA. On the other hand, the indoor density of Culex increased from 0.07 to 0.10 at 2-3 days post-MDA while the indoor parity rate of Culex did not change. The outdoor density of Anopheles in the IC increased (p = 0.394) from 0.58 to 0.90 at 2-3 days post-MDA; a similar observation was consistent for the outdoor density (2.83 to 3.90) and outdoor parity rate (70.59% to 97.44%) of Culex, while the outdoor parity rate of Anopheles reduced from 85.71 to 66.67% at 2-3 days post-MDA. A generalized linear model showed that ivermectin MDA significantly caused a reduction in both the indoor density (p < 0.001) and indoor parity rate (p = 0.003) of Anopheles in the IC.

CONCLUSION

Ivermectin MDA resulted in the reduction of both the survival and density of Anopheles mosquitoes. This has strong implications for malaria transmission, which depends strongly on vector survival.

Evaluation of Different Attractive Traps for Capturing Sand Flies (Diptera: Psychodidae) in an Endemic Area of Leishmaniasis, Southeast of Iran

Background:

The attraction of phlebotomine sand flies to plant and animal hosts is due to the produced chemical compounds, affecting the olfactory receptors of the insects. Therefore, novel and effective methods, such as Attractive Toxic Sugar Baits (ATSB) and Attractive Toxic Baits (ATB), are based on the effective materials that attract sand flies toward the host. The present study was designed to identify the attractive materials in plants and animals for using in ATSB and ATB.

Methods:

This cross-sectional study was carried out in July 2018 on endemic areas of leishmaniasis in Iran. Different baits, including mango, nectarine, grape, banana, melon and watermelon, defibrinated blood of cattle, sheep, goat and chicken, urine of cattle, sheep, goat and ultimately, simple and complex chemicals, such as CO₂, 1-octanol, lactic acid and human sweat were placed inside the traps, and the rate of the sand flies attraction to these materials was studied. Furthermore, data were analyzed using the Kruskal-Wallis test and Mann Whitney U test.

Results:

There was a significant difference in the sand flies attraction between the traps containing watermelon, urine of cattle, and sheep, and chemicals such as CO₂ and human sweat and the control trap (p< 0.05).

Conclusion:

This study showed that watermelon and CO₂ are the potential candidates for using in ATSB and ATB, respectively.

The Use of Granular Cyclopentanone as Alternative to Artificial Source of Carbon Dioxide in Improved Passive Outdoor Host Seeking Device (POHD)

Reliable sources of CO2 that are relatively cheap, obtainable, and easy to sustain are immediately required for scaling up of odor-baited mosquito surveillance and control devices. Several odor-baited devices are in the pipeline; however, their scale-up against residual malaria transmission, particularly in resource poor areas, is limited by the unavailability of reliable sources of CO2 and reliance on electrical power sources among other factors. We evaluated the use of granular cyclopentanone as an alternative to artificial or yeast fermentation-produced CO2 in passive outdoor host seeking device (POHD). Experiments were conducted against semifield reared An. arabiensis within the semifield system (SFS) at Ifakara Health Institute. Mosquitoes were tested against odor-baited POHDs augmented with yeast fermentation-produced CO2, granular cyclopentanone, attractive blends (Mbita or Ifakara), or their combinations. An insecticide, bendiocarb, was a killing agent used as a proxy for marking the mosquitoes visit the POHDs. Relative attractiveness of different treatment combinations was compared based on the proportion of dead mosquitoes that visited the POHD. The POHD augmented with granules of cyclopentanone alone was attractive to An. arabiensis as much as, or more than, POHDs augmented with yeast fermentation-produced CO2. The POHD baited with CO2 attracted more mosquitoes than those POHDs baited with synthetic blends alone; when these blends are combined with CO2, they attracted more mosquitoes than individual blends. More importantly, such POHDs baited with cyclopentanone attracted far greater proportion of mosquitoes than the POHD baited with either Mbita or Ifakara blend alone. The granular cyclopentanone strongly enhanced/potentiated the attractiveness of POHD baited with Mbita blends against mosquitoes compared to that of POHD baited with Ifakara blend. Moreover, the granular cyclopentanone retained its residual activity against An. arabiensis for up to 2 months after application particularly when used in combination with Mbita blend. In conclusion, this study demonstrates that cyclopentanone granules have the potential to substitute sources of CO2 in outdoor-based surveillance and control devices, thus warranting evaluation of such alternative under realistic field conditions.

Optimisation and field validation of odour-baited traps for surveillance of Aedes aegypti adults in Paramaribo, Suriname

BACKGROUND

Emerging arboviral diseases like Zika, dengue and chikungunya that are transmitted by Aedes aegypti mosquitoes, are increasingly threatening human health. Blends of human-like synthetic chemical attractants can be used to attract host-seeking mosquitoes. The aim of this study was to test new combinations of traps and odour baits in the laboratory, followed by testing the best candidates in the field to improve Ae. aegypti monitoring and surveillance.

METHODS

First, the BG-Suna trap was evaluated for capturing laboratory-reared Ae. aegypti by testing normal and inverted positions in screen cage tests. Secondly, the attractiveness of the MB5 blend, CO₂, and their combination was tested. Thirdly, we tested the attractiveness of different trap types (BG-Suna, BG-Sentinel, MM-X and CDC light trap). Finally, we confirmed laboratory results in the field in Paramaribo, Suriname, using the MB5 and BG-Lure odour blends, CO₂ and the BG-Sentinel and BG-Bowl trap using a Latin Square design.

RESULTS

The MB5 blend in combination with CO₂ outperformed traps baited only with CO₂ or MB5 in screen cage tests (P < 0.0001). The BG-Sentinel trap performed equally well as the inverted BG-Suna and was taken to the field (P = 0.729). In the field, we captured Ae. aegypti, Cx. quinquefasciatus and Cx. nigripalpus. We confirmed the laboratory results and found that the combination of the MB5 blend and CO₂ almost doubled Ae. aegypti female captures (P = 0.004) and more than doubled Culex spp. female captures (P = 0.005) compared to using only CO₂. Interestingly, the MB5 blend outperformed the commercially available BG-Lure, in the BG-Sentinel (P < 0.001). The BG-Bowl also attracted Ae. aegypti when baited with the MB5 blend in similar numbers as the BG-Sentinel baited with the MB5 (P = 0.362).

CONCLUSIONS

Our study demonstrated that the BG-Sentinel trap baited with the MB5 blend and CO₂ outperforms the current golden standard (BG-Sentinel trap with BG-Lure) for monitoring Ae. aegypti females and males, in both laboratory and field experiments. The BG-Bowl baited with the MB5 blend is a good candidate for home use. Finally, the results show that CO₂ is an indispensable component of the attractive blend.

Evaluation of an ultraviolet LED trap for catching Anopheles and Culex mosquitoes in south-eastern Tanzania

BACKGROUND

Improved surveillance techniques are required to accelerate efforts against major arthropod-borne diseases such as malaria, dengue, filariasis, Zika and yellow-fever. Light-emitting diodes (LEDs) are increasingly used in mosquito traps because they improve energy efficiency and battery longevity relative to incandescent bulbs. This study evaluated the efficacy of a new ultraviolet LED trap (Mosclean) against standard mosquito collection methods.

METHODS

The study was conducted in controlled semi-field settings and in field conditions in rural south-eastern Tanzania. The Mosclean trap was compared to commonly used techniques, namely CDC-light traps, human landing catches (HLCs), BG-Sentinel traps and Suna traps.

RESULTS

When simultaneously placed inside the same semi-field chamber, the Mosclean trap caught twice as many Anopheles arabiensis as the CDC-light trap, and equal numbers to HLCs. Similar results were obtained when traps were tested individually in the chambers. Under field settings, Mosclean traps caught equal numbers of An. arabiensis and twice as many Culex mosquitoes as CDC-light traps. It was also better at trapping malaria vectors compared to both Suna and BG-Sentinel traps, and was more efficient in collecting mosquitoes indoors than outdoors. The majority of An. arabiensis females caught by Mosclean traps were parous (63.6%) and inseminated (89.8%). In comparison, the females caught by CDC-light traps were 43.9% parous and 92.8% inseminated.

CONCLUSIONS

The UV LED trap (Mosclean trap) was efficacious for sampling Anopheles and Culex mosquitoes. Its efficacy was comparable to and in some instances better than traps commonly used for vector surveillance. The Mosclean trap was more productive in sampling mosquitoes indoors compared to outdoors. The trap can be used indoors near human-occupied nets, or outdoors, in which case additional CO2 improves catches. We conclude that this trap may have potential for mosquito surveillance. However, we recommend additional field tests to validate these findings in multiple settings and to assess the potential of LEDs to attract non-target organisms, especially outdoors.

Development of a More Effective Mosquito Trapping Box for Vector Control

Mosquito-borne diseases are a major public health issue in nearly all tropical and subtropical countries, making vector control imperative. The mosquito trapping box is one type of mosquito traps that is popular in some areas because it is affordable, environmentally friendly, and easy to produce. This research investigated whether the effectiveness of the mosquito trapping box could be increased through the addition of various physical factors, including a wooden frame, black cotton cloth, a fan, carbon dioxide (CO2), and heat, by testing a range of box designs in the Samut Songkhram Province, Thailand, between December 2016 and January 2017. We found that trapping boxes constructed with Pinus kesiya wood caught more mosquitoes than those constructed with two other types of wood or aluminum. We also found that mosquito trapping boxes were more effective when more factors were added, although these differences were only significant for black cotton cloth and CO2. These findings will guide the future development of mosquito trapping boxes for effective mosquito control in other areas, helping to reduce the incidence of mosquito-borne diseases.

Multiband modulation spectroscopy for the determination of sex and species of mosquitoes in flight

We present a dual-wavelength polarimetric measurement method to distinguish species and sexes of disease transmitting mosquitoes in flight. By measuring co- and de-polarized backscattered light at 808 and 1550 nm, the degree of linear polarization, wingbeat frequency, reflectance, spectral ratio and glossiness of mosquitoes can be retrieved. Body and wing contributions to these signals can be separated. Whereas the optical cross section is sensitive to the aspect of observation, thus the heading direction of the insect in flight, we demonstrate that polarimetric- and spectral-band ratios are largely invariant to the aspect of observation. We show that wing glossiness, as well as wing- and body-spectral ratios are particularly efficient in distinguishing Anopheles coluzzii and Anopheles arabiensis, 2 closely related species of malaria vectors. Spectral and polarimetric ratios relate to microstructural and melanization features of the wing and body of these species. We conclude that multiband modulation spectroscopy is a useful expansion of the parameter space that can be used to improve the specificity of entomological lidars.

Application of biogenic carbon dioxide produced by yeast with different carbon sources for attraction of mosquitoes towards adult mosquito traps

Surveillance is a prime requisite for controlling arthropod vectors like mosquitoes that transmit diseases such as malaria, dengue and chikungunya. Carbon dioxide (CO2) is one of the main cues from vertebrate breath that attracts mosquitoes towards the host. Hence, CO2 is used as an attractant during surveillance of mosquitoes either from commercial cylinders or dry ice for mosquito traps. In the present study, the biogenic carbon dioxide production was optimized with different carbon sources such as glucose, simple sugar and jaggery with and without yeast peptone dextrose (YPD) media using commercial baker's yeast. The results showed that yeast produced more biogenic CO2 with simple sugar as compared to other carbon sources. Further substrate concentration was optimized for the continuous production of biogenic CO2 for a minimum of 12 h by using 10 g of baker's yeast with 50 g of simple sugar added to 1.5 l distilled water (without YPD media) in a 2-l plastic bottle. This setup was applied in field condition along with two different mosquito traps namely Mosquito Killing System (MKS) and Biogents Sentinel (BGS) trap. Biogenic CO2 from this setup has increased the trapping efficiency of MKS by 6.48-fold for Culex quinquefasciatus, 2.62-fold for Aedes albopictus and 1.5-fold for Anopheles stephensi. In the case of BGS, the efficiency was found to be increased by 3.54-fold for Ae. albopictus, 4.33-fold for An. stephensi and 1.3-fold for Armigeres subalbatus mosquitoes. On the whole, plastic bottle setup releasing biogenic CO2 from sugar and yeast has increased the efficiency of MKS traps by 6.38-fold and 2.74-fold for BGS traps as compared to traps without biogenic CO2. The present study reveals that, among different carbon sources used, simple sugar as a substance (which is economical and readily available across the world) yielded maximum biogenic CO2 with yeast. This setup can be used as an alternative to CO2 cylinder and dry ice in any adult mosquito traps to enhance their trapping efficiency of a mosquito surveillance programme.

Multitasking roles of mosquito labrum in oviposition and blood feeding

Reception of odorants by two main head appendages, antennae and maxillary palps, is essential for insects' survival and reproduction. There is growing evidence in the literature suggesting that the proboscis is also an olfactory appendage and its function as an additional "antenna" has been previously proposed. We surmised that movements of the labrum toward a blood vessel might be chemically oriented and, if so, there should be odorant receptors expressed in the labrum. To test this hypothesis, we first compared by quantitative PCR expression of odorant receptors (OR) from the Southern house mosquito, Culex quinquefasciatus in antennae and proboscis and, subsequently compared OR expression in various proboscis parts. Our data suggested that a receptor for the oviposition attractant, skatole, CquiOR21, was not expressed in proboscis, whereas a receptor for another oviposition attractant, 4EP (4-ethylphenol), CquiOR99, and a receptorf for the insect repellent DEET, CquiOR136, were expressed in the stylet of the proboscis, particularly in the tip of the labrum. In a dual-choice olfactometer, mosquitoes having the stylet coated with nail polish were attracted to 4EP in the same manner as the untreated mosquitoes. By contrast, in an oviposition assay, the stylet-treated mosquitoes did not discriminate 4EP from control oviposition cups, whereas the untreated mosquitoes (as well as mosquitoes having the labella coated) laid significantly more egg rafts in cups treated with 4EP. Ablation experiments confirmed that 4EP was sensed by the labrum where CquiOR99 is highly expressed. Stylet-coated, labella-coated, and untreated mosquitoes laid significantly more egg rafts in skatole-treated cups than in control cups. Likewise, coating of proboscis structures with nail polish had no effect on DEET-mediated oviposition deterrence. In a behavioral arena designed to mimic a human arm, mosquitoes showed significantly reduced probing time when blood was impregnated with 4EP, i.e., they engaged more rapidly in continuous blood feeding as compared to untreated blood. The time of engagement for feeding in skatole-containing blood vs. untreated blood did not differ significantly. Taken together, these data suggest that 4EP reception by the labrum is important not only for oviposition decisions, but also for reducing probing and initiation of blood feeding.

Modification of the Suna Trap for Improved Survival and Quality of Mosquitoes in Support of Epidemiological Studies

Monitoring adult mosquito populations provides information that is critical for assessing risk of vector-borne disease transmission. The recently developed Suna trap was found to be a very effective trap when baited with an attractive odor blend. A modification of this trap was tested to improve its function as a tool for monitoring mosquito populations, including Anopheles coluzzii (An. gambiae sensu stricto molecular form M), Aedes aegypti, and Culex pipiens. The modified Suna trap (Suna-M) was altered by changing the position of the catch bag and the inclusion of a holding chamber in attempts to increase trapping efficacy and enhance the survival of mosquitoes. Each adaptation was tested in a dual-choice setup in a climate-controlled room against the original Suna trap and against 4 standard monitoring methods: the BG-sentinel (BGS), Centers for Disease Control and Prevention (CDC) light trap, Mosquito Magnet X (MM-X) trap, and human landing catch (HLC). No differences in trapping efficacy were observed between the original Suna trap and modified version; however, a version in which the funnel was extended with a box and supplemented with moistened cotton wool increased mosquito survival from 6.5% to 78.0% over 24 h. The HLC and BGS trap outperformed the Suna-M trap, whereas the MM-X and commonly used CDC light trap performed significantly less well than the Suna-M trap in the dual-choice setup. The performance of the Suna-M trap equaled the performance of the original Suna trap and could therefore be used for monitoring purposes. Although the HLC and BGS trap achieved higher catch sizes, the Suna trap has the advantage that it is standardized, does not place humans at risk, and is weather resistant. Field studies should be conducted to confirm that the Suna-M trap, baited with the odor blend, is an efficient and standardized tool to measure both indoor and outdoor disease transmission risk for a range of vector-borne diseases.

Trapping biases of Culex torrentium and Culex pipiens revealed by comparison of captures in CDC traps, ovitraps, and gravid traps

We evaluate three trapping methods for their effectiveness at capturing Culex pipiens and Culex torrentium, both enzootic vectors of bird-associated viruses in Europe. The comparisons, performed in two regions in Sweden, were among CDC traps baited with carbon dioxide, gravid traps, and ovitraps baited with hay infusion. The proportions of the two Culex species in a catch differed between trap types, with CDC traps catching a lower proportion of Cx. torrentium than both gravid traps and ovitraps. Between gravid traps and ovitraps, there was no difference in the proportions of the two species. The results indicate that Cx. torrentium may go undetected or underestimated compared to Cx. pipiens when using carbon dioxide baited CDC traps. The new insight of trap bias presented here adds an important dimension to consider when investigating these vectors of bird-associated viruses in the field.

Mosquito host preferences affect their response to synthetic and natural odour blends

BACKGROUND

The anthropophilic malaria mosquito Anopheles gambiae sensu stricto (hereafter termed Anopheles gambiae) primarily takes blood meals from humans, whereas its close sibling Anopheles arabiensis is more opportunistic. Previous studies have identified several compounds that play a critical role in the odour-mediated behaviour of An. gambiae. This study determined the effect of natural and synthetic odour blends on mosquitoes with different host preferences to better understand the host-seeking behaviour of mosquitoes and the potential of synthetic odour blends for standardized monitoring.

METHODS

Odour blends were initially tested for their attractiveness to An. gambiae and An. arabiensis in a semi-field system with MM-X traps baited with natural and synthetic odours. Natural host odours were collected from humans, cows and chickens. The synthetic odour blends consisted of three or five previously identified compounds released with carbon dioxide. These studies were continued under natural conditions where odour blends were tested outdoors to determine their effect on species with different host preferences.

RESULTS

In the semi-field experiments, human odour attracted significantly higher numbers of both mosquito species. However, An. arabiensis was also attracted to cow and chicken odours, which confirms its opportunistic behaviour. A five-component synthetic blend was highly attractive to both mosquito species. In the field, the synthetic odour blend caught significantly more An. funestus than traps baited with human odour, while no difference was found for An. arabiensis. Catches of An. arabiensis and Culex spp. contained large numbers of blood-fed mosquitoes, mostly from cows, which indicates that these mosquitoes had fed outdoors.

CONCLUSIONS

Different odour baits elicit varying responses among mosquito species. Synthetic odour blends are highly effective for trapping mosquitoes; however, not all mosquitoes respond equally to the same odour blend. Combining fermenting molasses with synthetic blends in a trap represents the most effective tool to catch blood-fed mosquitoes outside houses, which is essential for understanding outdoor malaria transmission.

Variation in Baiting Intensity Among CO2-Baited Traps Used to Collect Hematophagous Arthropods

Hematophagous arthropods transmit the etiological agents of numerous diseases and as a result are frequently the targets of sampling to characterize vector and pathogen populations. Arguably, the most commonly used sampling approach involves traps baited with carbon dioxide. We report results of a laboratory study in which the performance of carbon dioxide-baited traps was evaluated using measures of baiting intensity, the amount of carbon dioxide released per unit time during trap deployment. We evaluated the effects of trap design, carbon dioxide source, and wind speed on baiting intensity and documented significant effects of these factors on the length of sampling (time to baiting intensity = 0), maximum baiting intensity, and variation in baiting intensity during experimental trials. Among the three dry ice-baited trap types evaluated, traps utilizing insulated beverage coolers as dry ice containers sampled for the longest period of time, had the lowest maximum but most consistent baiting intensity within trials and were least sensitive to effects of wind speed and dry ice form (block vs. pellet) on baiting intensity. Results of trials involving traps baited with carbon dioxide released from pressurized cylinders suggested that this trap type had performance comparable to dry ice-baited insulated cooler traps but at considerably higher cost.

Is there an efficient trap or collection method for sampling Anopheles darlingi and other malaria vectors that can describe the essential parameters affecting transmission dynamics as effectively as human landing catches? - A Review

Distribution, abundance, feeding behaviour, host preference, parity status and human-biting and infection rates are among the medical entomological parameters evaluated when determining the vector capacity of mosquito species. To evaluate these parameters, mosquitoes must be collected using an appropriate method. Malaria is primarily transmitted by anthropophilic and synanthropic anophelines. Thus, collection methods must result in the identification of the anthropophilic species and efficiently evaluate the parameters involved in malaria transmission dynamics. Consequently, human landing catches would be the most appropriate method if not for their inherent risk. The choice of alternative anopheline collection methods, such as traps, must consider their effectiveness in reproducing the efficiency of human attraction. Collection methods lure mosquitoes by using a mixture of olfactory, visual and thermal cues. Here, we reviewed, classified and compared the efficiency of anopheline collection methods, with an emphasis on Neotropical anthropophilic species, especially Anopheles darlingi, in distinct malaria epidemiological conditions in Brazil.

Development and optimization of the Suna trap as a tool for mosquito monitoring and control

BACKGROUND

Monitoring of malaria vector populations provides information about disease transmission risk, as well as measures of the effectiveness of vector control. The Suna trap is introduced and evaluated with regard to its potential as a new, standardized, odour-baited tool for mosquito monitoring and control.

METHODS

Dual-choice experiments with female Anopheles gambiae sensu lato in a laboratory room and semi-field enclosure, were used to compare catch rates of odour-baited Suna traps and MM-X traps. The relative performance of the Suna trap, CDC light trap and MM-X trap as monitoring tools was assessed inside a human-occupied experimental hut in a semi-field enclosure. Use of the Suna trap as a tool to prevent mosquito house entry was also evaluated in the semi-field enclosure. The optimal hanging height of Suna traps was determined by placing traps at heights ranging from 15 to 105 cm above ground outside houses in western Kenya.

RESULTS

In the laboratory the mean proportion of An. gambiae s.l. caught in the Suna trap was 3.2 times greater than the MM-X trap (P < 0.001), but the traps performed equally in semi-field conditions (P = 0.615). As a monitoring tool , the Suna trap outperformed an unlit CDC light trap (P < 0.001), but trap performance was equal when the CDC light trap was illuminated (P = 0.127). Suspending a Suna trap outside an experimental hut reduced entry rates by 32.8% (P < 0.001). Under field conditions, suspending the trap at 30 cm above ground resulted in the greatest catch sizes (mean 25.8 An. gambiae s.l. per trap night).

CONCLUSIONS

The performance of the Suna trap equals that of the CDC light trap and MM-X trap when used to sample An. gambiae inside a human-occupied house under semi-field conditions. The trap is effective in sampling mosquitoes outside houses in the field, and the use of a synthetic blend of attractants negates the requirement of a human bait. Hanging a Suna trap outside a house can reduce An. gambiae house entry and its use as a novel tool for reducing malaria transmission risk will be evaluated in peri-domestic settings in sub-Saharan Africa.

Molasses as a source of carbon dioxide for attracting the malaria mosquitoes Anopheles gambiae and Anopheles funestus

BACKGROUND

Most odour baits for haematophagous arthropods contain carbon dioxide (CO2). The CO2 is sourced artificially from the fermentation of refined sugar (sucrose), dry ice, pressurized gas cylinders or propane. These sources of CO2 are neither cost-effective nor sustainable for use in remote areas of sub-Saharan Africa. In this study, molasses was evaluated as a potential substrate for producing CO2 used as bait for malaria mosquitoes.

METHODS

The attraction of laboratory-reared and wild Anopheles gambiae complex mosquitoes to CO2 generated from yeast-fermentation of molasses was assessed under semi-field and field conditions in western Kenya. In the field, responses of wild Anopheles funestus were also assessed. Attraction of the mosquitoes to a synthetic mosquito attractant, Mbita blend (comprising ammonia, L-lactic acid, tetradecanoic acid and 3-methyl-1-butanol) when augmented with CO2 generated from yeast fermentation of either molasses or sucrose was also investigated.

RESULTS

In semi-field, the release rate of CO2 and proportion of An. gambiae mosquitoes attracted increased in tandem with an increase in the quantity of yeast-fermented molasses up to an optimal ratio of molasses and dry yeast. More An. gambiae mosquitoes were attracted to a combination of the Mbita blend plus CO2 produced from fermenting molasses than the Mbita blend plus CO2 from yeast-fermented sucrose. In the field, significantly more female An. gambiae sensu lato mosquitoes were attracted to the Mbita blend augmented with CO2 produced by fermenting 500 g of molasses compared to 250 g of sucrose or 250 g of molasses. Similarly, significantly more An. funestus, Culex and other anopheline mosquito species were attracted to the Mbita blend augmented with CO2 produced from fermenting molasses than the Mbita blend with CO2 produced from sucrose. Augmenting the Mbita blend with CO2 produced from molasses was associated with high catches of blood-fed An. gambiae s.l. and An. funestus mosquitoes.

CONCLUSION

Molasses is a suitable ingredient for the replacement of sucrose as a substrate for the production of CO2 for sampling of African malaria vectors and other mosquito species. The finding of blood-fed malaria vectors in traps baited with the Mbita blend and CO2 derived from molasses provides a unique opportunity for the study of host-vector interactions.

Attraction of Ethiopian phlebotomine sand flies (Diptera: Psychodidae) to light and sugar-yeast mixtures (CO(2))

BACKGROUND

Visceral leishmaniasis (VL) known as Kala-Azar is a serious systemic disease caused by Leishmania donovani parasites (Trypanosomatidae: Kinetoplastida). The disease is prevalent in the Indian Sub-continent, East Africa and Brazil. In Africa, the worst affected regions are in Sudan, with an estimated 15,000-20,000 cases annually and Ethiopia with 5,000-7,000 cases a year. The main vector of VL in Sudan and Northern Ethiopia is Phlebotomus orientalis, a sand fly frequently found in association with Acacia spp and Balanite spp woodlands.

METHODS

To optimize sampling of sand flies for epidemiological studies in remote areas we tested different means of attraction. Miniature suction traps employing 2AA batteries (3 V) were deployed in the up-draft orientation and baited with chemical light-sticks (Red, Yellow and Green), or bakers' yeast in sugar solution (emitting CO2 and perhaps other attractants). These traps were compared with standard CDC incandescent light traps employing 6 V batteries. Trials were conducted during two consecutive years at different localities around Sheraro, a town in West Tigray, Northern Ethiopia.

RESULTS

The sand fly species composition was similar but not identical in the different locations tested with different Sergentomyia spp. predominating. Phlebotomus spp. comprised less than 1% of the catches during the first year trials (November - December 2011) but increased markedly during the second year trials performed later in the dry season at the height of the sand fly season in February 2012. Although there did not appear to be a species bias towards different light wave-lengths, fermenting yeast in sugar solution attracted relatively more Phlebotomus spp. and Sergentomyia schwetzi.

CONCLUSIONS

Although the standard 6 V CDC incandescent light traps captured more sand flies, light-weight (~350 g) 3 V suction traps baited with chemical light-sticks were shown to be effective means of monitoring sand flies. Such traps operated without light and baited with yeast in sugar solution caught relatively more Phlebotomus spp.

A novel synthetic odorant blend for trapping of malaria and other African mosquito species

Estimating the biting fraction of mosquitoes is of critical importance for risk assessment of malaria transmission. Here, we present a novel odor-based tool that has been rigorously assessed in semi-field assays and traditional African villages for estimating the number of mosquitoes that enter houses in search of a blood meal. A standard synthetic blend (SB) consisting of ammonia, (S)-lactic acid, tetradecanoic acid, and carbon dioxide was complemented with isovaleric acid, 4,5 dimethylthiazole, 2-methyl-1-butanol, and 3-methyl-1-butanol in various combinations and concentrations, and tested for attractiveness to the malaria mosquito Anopheles gambiae. Compounds were released through low density polyethylene (LDPE) material or from nylon strips (nylon). Studies were done in a semi-field facility and two traditional villages in western Kenya. The alcohol 3-methyl-1-butanol significantly increased the attraction of SB. The other compounds proved less effective or inhibitory. Tested in a village, 3-methyl-1-butanol, released from LDPE, increased the attraction of SB. Further studies showed a significantly enhanced attraction of adding 3-methyl-1-butanol to SB compared to previously-published attractive blends both under semi-field and village conditions. Other mosquito species with relevance for public health were collected with this blend in significantly higher numbers as well. These results demonstrate the advent of a novel, reliable odor-based sampling tool for the collection of malaria and other mosquitoes. The advantage of this odor-based tool over existing mosquito sampling tools is its reproducibility, objectiveness, and relatively low cost compared to current standards of CDC light traps or the human landing catch.

Carbon dioxide baited trap catches do not correlate with human landing collections of Anopheles aquasalis in Suriname

Three types of carbon dioxide-baited traps, i.e., the Centers for Disease Control Miniature Light Trap without light, the BioGents (BG) Sentinel Mosquito Trap (BG-Sentinel) and the Mosquito Magnet® Liberty Plus were compared with human landing collections in their efficiency in collecting Anopheles (Nyssorhynchus) aquasalis mosquitoes. Of 13,549 total mosquitoes collected, 1,019 (7.52%) were An. aquasalis. Large numbers of Culex spp were also collected, in particular with the (BG-Sentinel). The majority of An. aquasalis (83.8%) were collected by the human landing collection (HLC). None of the trap catches correlated with HLC in the number of An. aquasalis captured over time. The high efficiency of the HLC method indicates that this malaria vector was anthropophilic at this site, especially as carbon dioxide was insufficiently attractive as stand-alone bait. Traps using carbon dioxide in combination with human odorants may provide better results.

Evaluation of methods for sampling the malaria vector Anopheles darlingi (Diptera, Culicidae) in Suriname and the relation with its biting behavior

The effectiveness of CO2-baited and human-baited mosquito traps for the sampling of Anopheles darlingi Root was evaluated and compared with human landing collections in Suriname. Biting preferences of this mosquito on a human host were studied and related to trapping data. Traps used were the Centers for Disease Control and Prevention Miniature Light trap, the BG Sentinel mosquito trap, the Mosquito Magnet Liberty Plus mosquito trap (MM-Plus), and a custom-designed trap. Carbon dioxide and humans protected by a bed net were used as bait in the studies. The number of An. darlingi collected was greater with human landing collections than with all other collection methods. An. darlingi did not show a preference for protected humans over CO2 bait. The BG Sentinel mosquito trap with CO2 or human odor as bait and the MM-Plus proved the best alternative sampling tools for An. darlingi. The BG Sentinel mosquito trap with CO2 or human odor as bait was also very efficient at collecting Culex spp. In a field study on biting preferences of wild An. darlingi, the females showed directional biting behavior (P < 0.001), with a majority of females (93.3%) biting the lower legs and feet when approaching a seated human host. Higher efficiency of the closer-to-the-ground collecting MM-Plus and BG Sentinel mosquito trap when compared with the other trapping methods may be a result of a possible preference of this mosquito species for low-level biting. It is concluded that odor-baited sampling systems can reliably collect An. darlingi, but the odor bait needs to be improved, for instance, by including host-specific volatiles, to match live human baits.

Comparison of the efficacy of CO2-baited and unbaited light traps, gravid traps, backpack aspirators, and sweep net collections for sampling mosquitoes infected with Japanese encephalitis virus

Two field studies were conducted to determine the efficacy of mosquito collection methods for species composition, species abundance, and Japanese encephalitis virus infection rates in Taiwan. Traps evaluated included John W. Hock (JH) model UD black light traps, JH model 1012 new standard miniature CDC light traps, JH model 1712 CDC gravid traps, and Taiwan-made Pest-O-Lite light traps. Backpack aspirators and sweep nets were also used to collect the resting population. Culex tritaeniorhynchus in all studies and Mansonia uniformis in the Taipei areas were the two most abundance species collected. Dry ice-baited UD black light traps were effective in regard to species diversity, species abundance, and Japanese encephalitis virus infection rates. The unbaited Pest-O-Lite light traps collected significantly more female mosquitoes than the UD black light traps but performed similarly with regard to species diversity and male mosquito collection. Most mosquitoes collected by Pest-O-Lite light traps were dried and not suitable for virus detection. Dry ice-baited CDC light traps collected significantly fewer mosquitoes than other light traps. Although CO(2) -baited UD black light traps with octenol attracted more mosquitoes, no statistical significance was found compared to CO(2) -baited UD black light traps without octenol. Japanese encephalitis viruses were isolated from half of the positive pools in UD black light traps and CDC light traps.

Species composition of bacterial communities influences attraction of mosquitoes to experimental plant infusions

In the container habitats of immature mosquitoes, catabolism of plant matter and other organic detritus by microbial organisms produces metabolites that mediate the oviposition behavior of Aedes aegypti and Aedes albopictus. Public health agencies commonly use oviposition traps containing plant infusions for monitoring populations of these mosquito species, which are global vectors of dengue viruses. In laboratory experiments, gravid females exhibited significantly diminished responses to experimental infusions made with sterilized white oak leaves, showing that attractive odorants were produced through microbial metabolic activity. We evaluated effects of infusion concentration and fermentation time on attraction of gravid females to infusions made from senescent bamboo or white oak leaves. We used plate counts of heterotrophic bacteria, total counts of 4',6-diamidino-2-phenylindole-stained bacterial cells, and 16S ribosomal DNA (rDNA) polymerase chain reaction-denaturing gradient gel electrophoresis (DGGE) to show that changes in the relative abundance of bacteria and the species composition of bacterial communities influenced attraction of gravid A. aegypti and A. albopictus mosquitoes to infusions. DGGE profiles showed that bacterial species composition in infusions changed over time. Principal components analysis indicated that oviposition responses to plant infusions were in general most affected by bacterial diversity and abundance. Analysis of bacterial 16S rDNA sequences derived from DGGE bands revealed that Proteobacteria (Alpha-, Beta-, Delta-, and Gamma-) were the predominant bacteria detected in both types of plant infusions. Gravid A. aegypti were significantly attracted to a mix of 14 bacterial species cultured from bamboo leaf infusion. The oviposition response of gravid mosquitoes to plant infusions is strongly influenced by abundance and diversity of bacterial species, which in turn is affected by plant species, leaf biomass, and fermentation time.

Comparative efficacy of three suction traps for collecting phlebotomine sand flies (Diptera: Psychodidae) in open habitats

The efficacy of three suction traps for trapping phlebotomine sand flies (Diptera: Psychodidae) was compared. Traps were baited with Co(2) and used without any light source. CO(2)-baited CDC traps were evaluated either in their standard downdraft orientation or inverted (iCDC traps). Mosquito Magnet-X (MMX) counterflow geometry traps were tested in the updraft orientation only. Both updraft traps (iCDC and MMX) were deployed with their opening ∼10 cm from the ground while the opening of the downdraft (CDC) trap was ∼40 cm above ground. Comparisons were conducted in two arid locations where different sand fly species prevail. In the Jordan Valley, 3,367 sand flies were caught, 2,370 of which were females. The predominant species was Phlebotomus (Phlebotomus) papatasi, Scopoli 1786 (>99%). The updraft-type traps iCDC and MMX caught an average of 118 and 67.1 sand flies per trap night, respectively. The CDC trap caught 32.9 sand flies on average per night, significantly less than the iCDC traps. In the Judean desert, traps were arranged in a 3 × 3 Latin square design. A total of 565 sand flies were caught, 345 of which were females. The predominant species was P. (Paraphlebotomus) sergenti Parrot 1917 (87%). The updraft traps iCDC and MMX caught an average of 25.6 and 17.9 sand flies per trap per night, respectively. The CDC trap caught 7.8 sand flies on average per night, significantly less than the iCDC traps. The female to male ratio was 1.7 on average for all trap types. In conclusion, updraft traps deployed with their opening close to the ground are clearly more effective for trapping sand flies than downdraft CDC traps in open habitats.

Evaluation of two counterflow traps for testing behaviour-mediating compounds for the malaria vector Anopheles gambiae s.s. under semi-field conditions in Tanzania

BACKGROUND

Evaluation of mosquito responses towards different trap-bait combinations in field trials is a time-consuming process that can be shortened by experiments in contained semi-field systems. Possible use of the BG Sentinel (BGS) trap to sample Anopheles gambiae s.s. was evaluated. The efficiency of this trap was compared with that of the Mosquito Magnet-X (MM-X) trap, when baited with foot odour alone or combinations of foot odour with carbon dioxide (CO2) or lemongrass as behaviour-modifying cues.

METHODS

Female An. gambiae s.s. were released in an experimental flight arena that was placed in a semi-field system and left overnight. Catch rates for the MM-X and BGS traps were recorded. Data were analysed by fitting a generalized linear model to the (n+1) transformed catches.

RESULTS

Both types of traps successfully captured mosquitoes with all odour cues used. When the BGS trap was tested against the MM-X trap in a choice assay with foot odour as bait, the BGS trap caught about three times as many mosquitoes as the MM-X trap (P = 0.002). Adding CO2 (500 ml/min) to foot odour increased the number of mosquitoes caught by 268% for the MM-X (P < 0.001) and 34% (P = 0.051) for the BGS trap, compared to foot odour alone. When lemongrass leaves were added to foot odour, mosquito catches were reduced by 39% (BGS, P < 0.001) and 38% (MM-X, P = 0.353), respectively.

CONCLUSION

The BGS trap shows high potential for field trials due to its simple construction and high catch rate when baited with human foot odour only. However, for rapid screening of different baits in a contained semi-field system, the superior discriminatory power of the MM-X trap is advantageous.

Land use and mosquito diversity in the Peruvian Amazon

Anthropogenic environmental disturbance is a significant factor driving mosquito community composition. However, researchers subjectively define environmental change creating difficulties for cross-study comparison. To examine the relationship between terrestrial change and mosquito composition, we used remote sensing techniques to define spatially explicit land use categories along a gradient with low (rural), medium (peri-urban), and high (urban) anthropogenic influence in the Peruvian Amazon. We found significant differences in mosquito diversity among land use categories. Our results provide baseline data linking mosquito distribution to land use in the Peruvian Amazon and present an easily replicable method of comparison for future research. Creating standardized methods to measure the impact of human influence on the environment is of particular importance in designing targeted public health policies and in predicting disease risk in rapidly changing environments such as the Amazon.

Natural odor ligands for olfactory receptor neurons of the female mosquito Aedes aegypti: use of gas chromatography-linked single sensillum recordings

Female Aedes aegypti are vectors of dengue and yellow fever. Odor volatiles are the predominant cues that drive the host-seeking behavior of Ae. aegypti. Odorant molecules are detected and discriminated by olfactory receptor neurons (ORNs) housed in sensory hairs, sensilla, located on the antennae and maxillary palps. In a previous study, we used odor volatiles that are behaviorally and/or electrophysiologically active for Ae. aegypti and other mosquito species to show that antennal ORNs of female Ae. aegypti are divided into functionally different classes. In the present study, we have, for the first time, conducted gas chromatography-coupled single sensillum recordings (GC–SSR) from antennal trichoid and intermediate sensilla of female Ae. aegypti in order to screen for additional putative host attractants and repellents. We used headspace collections from biologically relevant sources, such as different human body parts (including feet, trunk regions and armpit), as well as a plant species used as a mosquito repellent, Nepeta faassenii. We found that a number of ORN types strongly responded to one or more of the biological extracts. GC–SSR recordings revealed several active components, which were subsequently identified through GC-linked mass spectrometry (GC–MS). Electrophysiologically active volatiles from human skin included heptanal, octanal, nonanal and decanal.

Towards a fuller understanding of mosquito behaviour: use of electrocuting grids to compare the odour-orientated responses of Anopheles arabiensis and An. quadriannulatus in the field

The epidemiological role of and control options for any mosquito species depend on its degree of 'anthropophily'. However, the behavioural basis of this term is poorly understood. Accordingly, studies in Zimbabwe quantified the effects of natural odours from cattle and humans, and synthetic components of these odours, on the attraction, entry and landing responses of Anopheles arabiensis Giles (Diptera: Culicidae) and Anopheles quadriannulatus Theobald. The numbers of mosquitoes attracted to human or cattle odour were compared using electrocuting nets (E-nets), and entry responses were gauged by the catch from an odour-baited entry trap (OBET) relative to that from an odour-baited E-net. Landing responses were estimated by comparing the catches from E-nets and cloth targets covered with an electrocuting grid. For An. arabiensis, E-nets baited with odour from a single ox or a single man caught similar numbers, and increasing the dose of human odour from one to three men increased the catch four-fold. For An. quadriannulatus, catches from E-nets increased up to six-fold in the progression: man, three men, ox, and man + ox, with catch being correlated with bait mass. Entry responses of An. arabiensis were stronger with human odour (entry response 62%) than with ox odour (6%) or a mixture of cattle and human odours (15%). For An. quadriannulatus, the entry response was low (< 2%) with both cattle and human odour. Anopheles arabiensis did not exhibit a strong entry response to carbon dioxide (CO2) (0.2-2 L/min). The trends observed using OBETs and E-nets also applied to mosquitoes approaching and entering a hut. Catches from an electrocuting target baited with either CO2 or a blend of acetone, 1-octen-3-ol, 4-methylphenol and 3-n-propylphenol - components of natural ox odour - showed that virtually all mosquitoes arriving there alighted on it. The propensity of An. arabiensis to enter human habitation seemed to be mediated by odours other than CO2 alone. Characterizing 'anthropophily' by comparing the numbers of mosquitoes caught by traps baited with different host odours can lead to spurious conclusions; OBETs baited with human odour caught around two to four times more An. arabiensis than cattle-baited OBETs, whereas a human-baited E-net caught less ( approximately 0.7) An. arabiensis than a cattle-baited E-net. Similar caution is warranted for other species of mosquito vectors. A fuller understanding of how to exploit mosquito behaviour for control and surveys requires wider approaches and more use of appropriate tools.

Effectiveness of mosquito traps in measuring species abundance and composition

Mosquito species abundance and composition estimates provided by trapping devices are commonly used to guide control efforts, but knowledge of trap biases is necessary for accurately interpreting results. We tested the hypothesis that commercially available traps (Mosquito Magnet-Pro, the Mosquito Magnet-X) would be significant improvements over the CDC Miniature Light Trap with respect to abundance, species diversity, and measures of recruitment in a wooded area of the Bronx Zoo in New York City, NY. The Mosquito Magnet-Pro collected significantly more mosquitoes (n = 1,117; mean per night, 124 +/- 28.3) than the CDC Miniature Light Trap (n = 167; mean per night, 19 +/- 5.5). The Simpson's diversity index was greatest for the Mosquito Magnet-Pro. A CDC light trap from a simultaneous surveillance project was located 15 m away and used as a control trap to test for significant differences in mosquito counts on nights with or without the experimental traps. There were no significant differences between nights, indicating the test traps did not recruit beyond 15 m. The traps differed significantly in abundance, but they had similarly limited sampling areas. Measured differences in abundance were independent of differences in diversity. This study highlights how differences between traps might affect species abundance and composition estimates.

Phytochemicals as population sampling lures

Most mosquito species have 2 hosts: vertebrate animals and vascular plants. The kairomones of vertebrates have been employed extensively as attractants in traps that are used for surveillance, either to assess adult density of mosquito populations or to detect pathogen activity. They also have been employed in basic field studies of mosquito physiology, behavior, and ecology. The semiochemicals that mosquitoes use to find plant hosts for their sugar, by contrast, have not been utilized at all. Currently we are characterizing attractive blends of volatile compounds produced by plant species visited by Aedes vexans, Culex pipiens, and Anopheles gambiae. These blends may be effective in attracting a unique subset of a mosquito population when deployed in surveillance traps. The principal advantages of phytochemical attractants are that they lure a) both sexes, b) all ages, including those that are newly emerged, c) females in all gonotrophic states, and d) both nondiapausing and reproductively diapausing females. Potential challenges to their successful use are the abundance of competing volatiles, narrow plant-host specificity, and a weaker behavioral response to phytochemical cues.

Evaluation of four sampling techniques for surveillance of Culex quinquefasciatus (Diptera: Culicidae) and other mosquitoes in African rice agroecosystems

Field studies were conducted in a rice, Oryza sativa L., agroecosystem in Mwea Kenya to compare the efficiency of CO2-baited Centers for Disease Control (CDC) light traps against nonbaited CDC light traps and gravid traps against oviposition traps in outdoor collection of Culex quinquefasciatus Say (Diptera: Culicidae) and other mosquitoes. Collectively, 21 mosquito species from the genera Culex, Anopheles, Mansonia, Ficalbia, and Aedes were captured during the 10-wk study period. Cx. quinquefasciatus was the predominant species in all trap types with proportions ranging from 57% in the nonbaited CDC light traps to 95% in the gravid traps. Significantly higher numbers of Cx. quinquefasciatus and Culex annulioris Theobald were collected in the CO2-baited CDC light traps than in the nonbaited CDC light traps, but the numbers of other mosquito species, including malaria vectors Anopheles arabiensis Patton and Anopheles funestus Giles did not differ significantly between the two trap types. More Cx. quinquefasciatus females were collected in grass infusion-baited gravid traps than egg rafts of this species in oviposition traps containing the same infusion. Although most mosquitoes captured in CO,-baited and nonbaited CDC light traps were unfed, most of those collected in gravid traps were gravid. From these findings, it is concluded that at least in the rice-growing area of Mwea Kenya, CO2-baited CDC light traps in conjunction with gravid traps can be used in monitoring of Cx. quinquefasciatus both for control and disease surveillance.

Trapping of the malaria vector Anopheles gambiae with odour-baited MM-X traps in semi-field conditions in western Kenya

BACKGROUND

The successful development of odour-baited trapping systems for mosquitoes depends on the identification of behaviourally active semiochemicals, besides the design and operating principles of such devices. A large variety of 'attractants' has been identified in laboratory investigations, yet few of these increase trap catches in the field. A contained system, intermediate between the laboratory and open field, is presented and previous reports that human foot odour induces behavioural responses of Anopheles gambiae confirmed.

METHODS

The response of 3-5 day old female An. gambiae towards odour-baited counterflow geometry traps (MM-X model; American Biophysics Corp., RI) was studied in semi-field (screen house) conditions in western Kenya. Traps were baited with human foot odour (collected on socks), carbon dioxide (CO2, 500 ml min(-1)), ammonia (NH3), 1-octen-3-ol, or various combinations thereof. Trap catches were log (x+1) transformed and subjected to Latin square analysis of variance procedures.

RESULTS

Apart from 1-octen-3-ol, all odour baits caused significant (P < 0.05) increases in trap catches over non-baited traps. Foot odour remained behaviourally active for at least 8 days after collection on nylon or cotton sock fabric. A synergistic response (P < 0.001) was observed towards the combination of foot odour and CO2, which increased catches of these odours alone by 3.8 and 2.7 times, respectively.

CONCLUSION

These results are the first to report behavioural responses of an African malaria vector to human foot odour outside the laboratory, and further investigation of fractions and/or individual chemical components of this odour complex are called for. Semi-field systems offer the prospect of high-throughput screening of candidate kairomones, which may expedite the development of efficient trap-bait systems for this and other African mosquito species.

Comparison of plume structures of carbon dioxide emitted from different mosquito traps

A large field wind tunnel was used to compare four types of CO2-baited mosquito traps. This study compared the plume structure and concentration of CO2 emitted by each trap, flow of suction into the trapping systems, flow of CO2 being released, trap shape and configuration, differences in visual appearance, and differences in temperature and humidity of emissions at the source of CO2 compared to ambient air. The structure of the CO2 plumes emitted by each trap differed considerably. All four plumes were turbulent, causing the concentration of CO2 within several metres of the source to attenuate to between 375 and 875 p.p.m. The Encephalitis Virus Surveillance (EVS) trap emitted concentrations of CO2 exceeding 20,000 p.p.m., the detection limits of our equipment, whereas the Mosquito Magnet Freedom (MMF), Mosquito Magnet Liberty (MML) and Mosquito Magnet X (MMX) traps released CO2 at peaks of about 3500, 7200 and 8700 p.p.m., respectively. The MMX trap produced the greatest air velocity at both the suction inlet and CO2 outlet, followed by the MMF, MML and the EVS traps, respectively.

Orientation of Culex mosquitoes to carbon dioxide-baited traps: flight manoeuvres and trapping efficiency

Females of Culex quinquefasciatus Say and Culex tarsalis Coquillet (Diptera: Culicidae) in the host-seeking stage were released and video recorded in three dimensions in a large field wind tunnel as they flew to four kinds of CO2-baited mosquito traps. The trapping efficiency (number of mosquitoes approaching compared to the number caught) was determined for each trap type. The Encephalitis Virus Surveillance (EVS), Mosquito Magnet Freedom (MMF) and Mosquito Magnet Liberty (MML) traps captured only 13-16% of approaching Cx. quinquefasciatus females, whereas the Mosquito Magnet-X (MMX) trap captured 58%. Similar results were obtained for Cx. tarsalis. Orientation behaviour and flight parameters of mosquitoes approaching the four traps were compared. Mosquitoes spent the most time orienting to the EVS trap. Flight speed decreased as mosquitoes entered the vicinity of each trap and a large portion of their time was spent within 30 cm downwind of the traps. Flights became highly tortuous downwind of the poorly performing traps and just upwind of the MMX trap. Differences between traps and possible explanations for the superior performance of the MMX trap are considered.

Evaluation of candidate traps as tools for conducting surveillance for Anopheles mosquitoes in a malaria-endemic area in western Thailand

The effectiveness of five mosquito traps at sampling anopheline mosquitoes was compared with landing/biting (L/B) collections in western Thailand. Traps evaluated included a CDC style light trap (CDC LT) with dry ice, the American Biophysics Corporation (ABC) standard light trap (ABC LT) with dry ice and octenol, the ABC counterflow geometry (CFG) trap with dry ice and octenol, the ABC mosquito magnet (MM) trap with octenol, and the Nicosia and Reinhardt Company Mosquito Attractor Device (N&R trap). Mosquito numbers captured in landing-biting collections were 5.2, 7.0, 7.3, 31.1, and 168.8 times greater than those collected in the ABC LT, MM, CDC LT, CFG, and N&R traps, respectively, for Anopheles minimus Theobald, the predominant malaria vector in the region. Similar results were obtained for the secondary malaria vectors Anopheles maculatus Theobald and Anopheles sawadwongporni Rattanarithikul & Green. Only Anopheles kochi Doenitz was collected in significantly greater numbers in the CDC LT, ABC LT, and MM traps compared with L/B collections. Although none of the traps were as effective as L/B collections, the ABC LT, MM, and CDC LT were the best alternatives to human bait for the collection of anopheline malaria vectors in Thailand.

Allomonal effect of breath contributes to differential attractiveness of humans to the African malaria vector Anopheles gambiae

BACKGROUND: Removal of exhaled air from total body emanations or artificially standardising carbon dioxide (CO2) outputs has previously been shown to eliminate differential attractiveness of humans to certain blackfly (Simuliidae) and mosquito (Culicidae) species. Whether or not breath contributes to between-person differences in relative attractiveness to the highly anthropophilic malaria vector Anopheles gambiae sensu stricto remains unknown and was the focus of the present study. METHODS: The contribution to and possible interaction of breath (BR) and body odours (BO) in the attraction of An. gambiae s.s. to humans was investigated by conducting dual choice tests using a recently developed olfactometer. Either one or two human subjects were used as bait. The single person experiments compared the attractiveness of a person's BR versus that person's BO or a control (empty tent with no odour). His BO and total emanations (TE = BR+BO) were also compared with a control. The two-person experiments compared the relative attractiveness of their TE, BO or BR, and the TE of each person against the BO of the other. RESULTS: Experiments with one human subject (P1) as bait found that his BO and TE collected more mosquitoes than the control (P = 0.005 and P < 0.001, respectively), as did his BO and the control versus his BR (P < 0.001 and P = 0.034, respectively). The TE of P1 attracted more mosquitoes than that of another person designated P8 (P < 0.021), whereas the BR of P8 attracted more mosquitoes than the BR of P1 (P = 0.001). The attractiveness of the BO of P1 versus the BO of P8 did not differ (P = 0.346). The BO from either individual was consistently more attractive than the TE from the other (P < 0.001). CONCLUSIONS: We demonstrated for the first time that human breath, although known to contain semiochemicals that elicit behavioural and/or electrophysiological responses (CO2, ammonia, fatty acids) in An. gambiae also contains one or more constituents with allomonal (~repellent) properties, which inhibit attraction and may serve as an important contributor to between-person differences in the relative attractiveness of humans to this important malaria vector.

Phlebotomine sandfly responses to carbon dioxide and human odour in the field

Responses of Lutzomyia sandflies (Diptera: Psychodidae: Phlebotominae) to carbon dioxide (CO2) and human odour were investigated by field experiments in Parana State, southern Brazil. Catches of two predominant species: Lu. intermedia (Antunes & Coutinho) and Lu. whitmani Lutz & Neiva, were compared between traps baited with a human adult or with CO2 emitted at the human-equivalent rate. When the baits were only 40 cm apart, no difference of attractiveness was detected. When baits were separated by 20 m, however, significantly fewer sandflies (44% Lu. intermedia, 46% Lu. whitmani) were trapped with CO2 compared with human bait. This is the first field evidence that anthropophilic sandflies are attracted by human kairomones in addition to CO2. For both species [Lutzomyia intermedia and Lu. whitmani] [corrected], the proportion of human attractiveness attributable to CO2 was significantly more [corrected] for males than females; for Lu. intermedia males human bait was no more attractive than CO2 alone. Gender differences in sandfly olfactory sensitivity are likely to be associated with behavioural differences on the host, where females feed on blood and males find mates. With traps 20 m apart, both Lutzomyia spp. showed roughly linear increased responses (log-log scale) to 0.08-0.55% CO2 equivalent to 0.5-4 humans. This would explain why host size is generally proportional to attractiveness, as observed for other species of phlebotomine sandflies.

The response of Culex quinquefasciatus (Diptera: culicidae) to traps baited with carbon dioxide, 1-octen-3-ol, acetone, butyric acid and human foot odour in Tanzania

The responses of Culex quinquefasciatus Say to traps baited with carbon dioxide, 1-octen-3-ol, acetone, butyric acid and human foot odour were studied in the field in Muheza, north-east Tanzania using Counterflow Geometry (CFG) and Centers for Disease Control (CDC) traps. It was found that significantly more C. quinquefasciatus responded to foot odour collected on nylon stockings than to clean nylon stockings (P < 0.05). Significantly more mosquitoes were caught in a CFG trap baited with carbon dioxide than in traps with either human foot odour, acetone or butyric acid. It was also found that in an outdoor situation a carbon dioxide baited CDC unlit trap collected over 12 times more C. quinquefasciatus than an unbaited CDC unlit trap and nine times more mosquitoes than CDC traps baited with 1-octen-3-ol alone (P < 0.05). The number of mosquitoes caught in a CDC trap baited with 1-octen-3-ol did not differ significantly from that of the unbaited CDC trap (P > 0.05). These results indicate that the Afrotropical C. quinquefasciatus respond significantly better to traps baited with carbon dioxide than to either octenol, acetone or butyric acid, and that human foot odour contains stimuli to which C. quinquefasciatus is attracted under field conditions.