scholarly journals Passive Outdoor Host Seeking Device (POHD): Designing and Evaluation against Outdoor Biting Malaria Vectors

2020 ◽  
Vol 2020 ◽  
pp. 1-15
Author(s):  
Stella T. Kessy ◽  
Ladslaus L. Mnyone ◽  
Bruno A. Nyundo ◽  
Issa N. Lyimo
Keyword(s):  
Carbon Dioxide ◽  
Malaria Transmission ◽  
Indoor Residual Spraying ◽  
Malaria Vectors ◽  
Natural Environments ◽  
Release Formulation ◽  
Experimental Hut ◽  
Host Seeking ◽  
Outdoor Biting ◽  
Residual Malaria Transmission

Odor-baited devices are increasingly needed to compliment long-lasting insecticidal nets (LLINs) and indoor residual spraying (IRS) for control of residual malaria transmission. However, the odor-baited devices developed so far are bulky, dependent on the source of electricity and carbon dioxide (CO2), and they are logistically unsuitable for scaling up in surveillance and control of malaria vectors. We designed a passive and portable outdoor host seeking device (POHD) and preliminarily evaluated suitable components against Anopheles arabiensis that maintains residual malaria transmission. Experiments were conducted using semifield reared An. arabiensis within the semifield system at Ifakara Health Institute (IHI) in southeastern Tanzania. These mosquitoes were exposed to Suna traps® baited with BG lures or source of light and augmented with carbon dioxide (CO2) in view of identifying best attractants necessary to improve attractiveness of designed POHD. Two Suna traps® were hanged at the corner but outside the experimental hut in a diagonal line and rotated between four corners to control for the effect of position and wind direction on mosquito catches. Furthermore, mosquitoes were also exposed to either a bendiocarb-treated or bendiocarb-untreated POHD baited with Mbita blend, Ifakara blend, and worn socks and augmented with warmth (i.e., 1.5 liter bottle of warm water) inside an experimental hut or a screened rectangular box. This study demonstrated that mosquitoes were more strongly attracted to Suna trap® baited with BG lures and CO2 relative to those traps baited with a source of light and CO2. The POHD baited with synthetic blends attracted and killed greater proportion of An. arabiensis compared with POHD baited with worn socks. Efficacy of the POHD was unaffected by source of warmth, and it was reduced by about 50% when the device was tested inside a screened rectangular box relative to closed experimental hut. Overall, this study demonstrates that the POHD baited with synthetic blends (Mbita and Ifakara blends) and bendiocarb can effectively attract and kill outdoor biting malaria vector species. Such POHD baited with synthetic blends may require the source of CO2 to enhance attractiveness to mosquitoes. Further trials are, therefore, ongoing to evaluate attractiveness of improved design of POHD baited with slow-release formulation of synthetic blends and sustainable source of CO2 to malaria vectors under semifield and natural environments.

scholarly journals Creating mosquito-free outdoor spaces using transfluthrin-treated chairs and ribbons

2019 ◽  
Author(s):  
John Paliga Masalu ◽  
Marceline Finda ◽  
Gerry F. Killeen ◽  
Halfan S. Ngowo ◽  
Polius G. Pinda ◽  
...  
Keyword(s):  
Anopheles Funestus ◽  
Indoor Residual Spraying ◽  
Malaria Vectors ◽  
Insecticide Treated Nets ◽  
Domestic Spaces ◽  
Host Seeking ◽  
Outdoor Spaces ◽  
Outdoor Biting ◽  
Outdoor Environments ◽  
Almost All

Abstract Background Residents of malaria-endemic communities spend several hours outdoors performing different activities, e.g. cooking, story-telling or eating, thereby exposing themselves to potentially-infectious mosquitoes. This compromises effectiveness of indoor interventions, notably long-lasting insecticide-treated nets (LLINs) and indoor residual spraying (IRS). This study characterized common peri-domestic spaces in rural south-eastern Tanzania, and assessed protective efficacies of hessian fabric mats and ribbons treated with the spatial repellent, transfluthrin and respectively fitted to chairs and outdoor kitchens, against mosquitoes.Methods Two hundred households were surveyed, and their most-used peri-domestic spaces physically characterized. Protective efficacies of locally-made transfluthrin-emanating chairs and hessian ribbons were tested in outdoor environments of eight households using volunteer-occupied exposure-free double net traps. CDC light traps were used to estimate host-seeking mosquito densities within open-structure outdoor kitchens. Field-collected Anopheles arabiensis and Anopheles funestus mosquitoes were exposed underneath the chairs to estimate 24h-mortality. Finally, WHO insecticide susceptibility tests were conducted on wild-caught Anopheles from the villages.Results Approximately half (52%) of houses had verandas. Aside from these verandas, most houses also had peri-domestic spaces where residents stayed most times (67% of houses with verandas and 94% of non-veranda houses). Two-thirds of these spaces were sited under trees, and only one third (34.4%) were built-up. The outdoor structures were usually makeshift kitchens having roofs and partial walls. Transfluthrin-treated chairs reduced outdoor-biting An. arabiensis densities by 70-76% while transfluthrin-treated hessian ribbons fitted to the outdoor kitchens caused 81% reduction in the general peri-domestic area. Almost all the field-collected An. arabiensis (99.4%) and An. funestus (100%) exposed under transfluthrin-treated chairs died. The An. arabiensis were susceptible to non-pyrethroids (pirimiphos methyl & bendiocarb) but resistant to pyrethroids commonly used on LLINs (deltamethrin & permethrin).Conclusion Most houses had actively-used peri-domestic outdoor spaces where exposure to mosquitoes occurred. The transfluthrin-treated chair and ribbons reduced outdoor-biting malaria vectors in these peri-domestic spaces, and also elicited significant mortality among pyrethroid-resistant field-caught malaria vectors. These two new prototype formats for transfluthrin emanators, if developed further, may constitute new options for complementing LLINs and IRS with outdoor protection against malaria and other mosquito-borne pathogens in areas where peri-domestic human activities are common.

scholarly journals Creating mosquito-free outdoor spaces using transfluthrin-treated chairs and ribbons

2020 ◽  
Author(s):  
John Paliga Masalu ◽  
Marceline Finda ◽  
Gerry F. Killeen ◽  
Halfan S. Ngowo ◽  
Polius G. Pinda ◽  
...  
Keyword(s):  
Anopheles Funestus ◽  
Indoor Residual Spraying ◽  
Malaria Vectors ◽  
Insecticide Treated Nets ◽  
Domestic Spaces ◽  
Host Seeking ◽  
Outdoor Spaces ◽  
Outdoor Biting ◽  
Outdoor Environments ◽  
Almost All

Abstract Background: Residents of malaria-endemic communities spend several hours outdoors performing different activities, e.g. cooking, story-telling or eating, thereby exposing themselves to potentially-infectious mosquitoes. These behaviors compromise effectiveness of indoor interventions, notably long-lasting insecticide-treated nets (LLINs) and indoor residual spraying (IRS). This study characterized common peri-domestic spaces in rural south-eastern Tanzania, and assessed protective efficacies of hessian fabric mats and ribbons treated with the spatial repellent, transfluthrin and respectively fitted to chairs and outdoor kitchens, against mosquitoes. Methods : Two hundred households were surveyed, and their most-used peri-domestic spaces physically characterized. Protective efficacies of locally-made transfluthrin-emanating chairs and hessian ribbons were tested in outdoor environments of 28 households in dry and wet seasons, using volunteer-occupied exposure-free double net traps. CDC light traps were used to estimate host-seeking mosquito densities within open-structure outdoor kitchens. Field-collected Anopheles arabiensis and Anopheles funestus mosquitoes were exposed underneath the chairs to estimate 24h-mortality. Finally, WHO insecticide susceptibility tests were conducted on wild-caught Anopheles from the villages. Results : Approximately half (52%) of houses had verandas. Aside from these verandas, most houses also had peri-domestic spaces where residents stayed most times (67% of houses with verandas and 94% of non-veranda houses). Two-thirds of these spaces were sited under trees, and one third (34.4%) were built-up. The outdoor structures were usually makeshift kitchens having roofs and partial walls. Transfluthrin-treated chairs reduced outdoor-biting An. arabiensis densities by 70-85%, while transfluthrin-treated hessian ribbons fitted to the outdoor kitchens caused 77-81% reduction in the general peri-domestic area. Almost all the field-collected An. arabiensis (99.4%) and An. funestus (100%) exposed under transfluthrin-treated chairs died. The An. arabiensis were susceptible to non-pyrethroids (pirimiphos methyl & bendiocarb) but resistant to pyrethroids commonly used on LLINs (deltamethrin & permethrin). Conclusion: Most houses had actively-used peri-domestic outdoor spaces where exposures to mosquitoes occur. Both the transfluthrin-treated chairs and ribbons reduced outdoor-biting malaria vectors in the peri-domestic spaces, and elicited significant mortality among pyrethroid-resistant field-caught malaria vectors. These two prototype formats, if developed further, may constitute new options for complementing LLINs and IRS with outdoor protection against malaria and other mosquito-borne diseases in areas with significant peri-domestic activities. Keywords : Peri-domestic spaces, transfluthrin-treated chairs, eave ribbons, transfluthrin, spatial repellents, outdoor-biting, malaria vectors, Ifakara Health Institute.

scholarly journals Evaluation of different deployment strategies for larviciding to control malaria: a simulation study

2021 ◽  
Vol 20 (1) ◽  
Author(s):  
Manuela Runge ◽  
Salum Mapua ◽  
Ismail Nambunga ◽  
Thomas A. Smith ◽  
Nakul Chitnis ◽  
...  
Keyword(s):  
Malaria Transmission ◽  
Critical Role ◽  
Indoor Residual Spraying ◽  
Malaria Prevalence ◽  
Transmission Model ◽  
Malaria Vectors ◽  
Relative Reduction ◽  
Insecticide Treated Nets ◽  
Host Seeking ◽  
The Impact

Abstract Background Larviciding against malaria vectors in Africa has been limited to indoor residual spraying and insecticide-treated nets, but is increasingly being considered by some countries as a complementary strategy. However, despite progress towards improved larvicides and new tools for mapping or treating mosquito-breeding sites, little is known about the optimal deployment strategies for larviciding in different transmission and seasonality settings. Methods A malaria transmission model, OpenMalaria, was used to simulate varying larviciding strategies and their impact on host-seeking mosquito densities, entomological inoculation rate (EIR) and malaria prevalence. Variations in coverage, duration, frequency, and timing of larviciding were simulated for three transmission intensities and four transmission seasonality profiles. Malaria transmission was assumed to follow rainfall with a lag of one month. Theoretical sub-Saharan African settings with Anopheles gambiae as the dominant vector were chosen to explore impact. Relative reduction compared to no larviciding was predicted for each indicator during the simulated larviciding period. Results Larviciding immediately reduced the predicted host-seeking mosquito densities and EIRs to a maximum that approached or exceeded the simulated coverage. Reduction in prevalence was delayed by approximately one month. The relative reduction in prevalence was up to four times higher at low than high transmission. Reducing larviciding frequency (i.e., from every 5 to 10 days) resulted in substantial loss in effectiveness (54, 45 and 53% loss of impact for host-seeking mosquito densities, EIR and prevalence, respectively). In seasonal settings the most effective timing of larviciding was during or at the beginning of the rainy season and least impactful during the dry season, assuming larviciding deployment for four months. Conclusion The results highlight the critical role of deployment strategies on the impact of larviciding. Overall, larviciding would be more effective in settings with low and seasonal transmission, and at the beginning and during the peak densities of the target species populations. For maximum impact, implementers should consider the practical ranges of coverage, duration, frequency, and timing of larviciding in their respective contexts. More operational data and improved calibration would enable models to become a practical tool to support malaria control programmes in developing larviciding strategies that account for the diversity of contexts.

scholarly journals Bionomics and ecology of Anopheles merus along the East and Southern Africa coast

2021 ◽  
Vol 14 (1) ◽  
Author(s):  
Brian Bartilol ◽  
Irene Omedo ◽  
Charles Mbogo ◽  
Joseph Mwangangi ◽  
Martin K. Rono
Keyword(s):  
Malaria Transmission ◽  
Mosquito Species ◽  
Scale Up ◽  
Indoor Residual Spraying ◽  
Temporal Distribution ◽  
Malaria Vectors ◽  
Behavioural Plasticity ◽  
Insecticide Treated Nets ◽  
Resting Behaviour ◽  
Residual Malaria Transmission

AbstractMalaria transmission persists despite the scale-up of interventions such as long-lasting insecticide-treated nets (LLINs) and indoor residual spraying (IRS). Understanding the entomological drivers of transmission is key for the design of effective and sustainable tools to address the challenge. Recent research findings indicate a shift in vector populations from the notorious Anopheles gambiae (s.s.) as a dominant vector to other species as one of the factors contributing to the persistence of malaria transmission. However, there are gaps in the literature regarding the minor vector species which are increasingly taking a lead role in malaria transmission. Currently, minor malaria vectors have behavioural plasticity, which allows their evasion of vector control tools currently in use. To address this, we have reviewed the role of Anopheles merus, a saltwater mosquito species that is becoming an important vector of malaria transmission along the East and Southern African coast. We performed a literature review from PubMed and Google Scholar and reviewed over 50 publications relating to An. merus's bionomics, taxonomy, spatial-temporal distribution and role in malaria transmission. We found that An. merus is an important vector of malaria and that it contributes to residual malaria transmission because of its exophilic tendencies, insecticide resistance and densities that peak during the dry seasons as the freshwater mosquitoes decline. Spatial and temporal studies have also shown that this species has increased its geographical range, densities and vectorial capacity over time. In this review, we highlight the resting behaviour and breeding habitats of this mosquito, which could be targeted for surveillance studies and control interventions.

scholarly journals Mosquito feeding behavior and how it influences residual malaria transmission across Africa

2019 ◽  
Vol 116 (30) ◽  
pp. 15086-15095 ◽  
Author(s):  
Ellie Sherrard-Smith ◽  
Janetta E. Skarp ◽  
Andrew D. Beale ◽  
Christen Fornadel ◽  
Laura C. Norris ◽  
...  
Keyword(s):  
Vector Control ◽  
Indoor Residual Spraying ◽  
Malaria Prevention ◽  
Health Impact ◽  
Time Of Day ◽  
Malaria Vectors ◽  
Bed Nets ◽  
Outdoor Biting ◽  
Residual Malaria Transmission ◽  
Year 2000

The antimalarial efficacy of the most important vector control interventions—long-lasting insecticidal nets (LLINs) and indoor residual spraying (IRS)—primarily protect against mosquitoes’ biting people when they are in bed and indoors. Mosquito bites taken outside of these times contribute to residual transmission which determines the maximum effectiveness of current malaria prevention. The likelihood mosquitoes feed outside the time of day when LLINs and IRS can protect people is poorly understood, and the proportion of bites received outdoors may be higher after prolonged vector control. A systematic review of mosquito and human behavior is used to quantify and estimate the public health impact of outdoor biting across Africa. On average 79% of bites by the major malaria vectors occur during the time when people are in bed. This estimate is substantially lower than previous predictions, with results suggesting a nearly 10% lower proportion of bites taken at the time when people are beneath LLINs since the year 2000. Across Africa, this higher outdoor transmission is predicted to result in an estimated 10.6 million additional malaria cases annually if universal LLIN and IRS coverage was achieved. Higher outdoor biting diminishes the cases of malaria averted by vector control. This reduction in LLIN effectiveness appears to be exacerbated in areas where mosquito populations are resistant to insecticides used in bed nets, but no association was found between physiological resistance and outdoor biting. Substantial spatial heterogeneity in mosquito biting behavior between communities could contribute to differences in effectiveness of malaria control across Africa.

Patterns of human exposure to early evening and outdoor biting mosquitoes and residual malaria transmission in Ethiopia

Acta Tropica ◽  
2021 ◽  
Vol 216 ◽  
pp. 105837
Author(s):  
Teshome Degefa ◽  
Andrew K. Githeko ◽  
Ming-Chieh Lee ◽  
Guiyun Yan ◽  
Delenasaw Yewhalaw
Keyword(s):  
Malaria Transmission ◽  
Human Exposure ◽  
Early Evening ◽  
Outdoor Biting ◽  
Residual Malaria Transmission

scholarly journals Semifield Evaluation of Improved Passive Outdoor Host Seeking Device (POHD) for Outdoor Control of Anopheles arabiensis Mosquitoes

2020 ◽  
Vol 2020 ◽  
pp. 1-11
Author(s):  
Stella T. Kessy ◽  
Bruno A. Nyundo ◽  
Ladslaus L. Mnyone ◽  
Issa N. Lyimo
Keyword(s):  
Carbon Dioxide ◽  
Anopheles Arabiensis ◽  
Mosquito Control ◽  
Real Life ◽  
Residual Activity ◽  
Optimal Placement ◽  
Treatment Combination ◽  
Host Seeking ◽  
Outdoor Biting ◽  
Control Devices

Despite the considerable progress made so far, the effectiveness and mass application of odour-baited outdoor mosquito control devices in pipelines is limited by several factors. These include the design and size of the devices, optimal placement of attractive blends, and nature of materials into which the blends are impregnated. The primary aim of this study was to manipulate these factors to improve the attractiveness of our recently developed passive outdoor host seeking device (POHD) to outdoor biting Anopheles arabiensis. Specifically, the study aimed to determine optimal placement of odour blends and killing bioactives in POHD for maximum attraction and killing of An. arabiensis and to assess the effects of blend types, formulation, and residual activity on attractiveness of the POHD to An. arabiensis. The POHDs baited with attractive blends, carbon dioxide (CO2), and bendiocarb-treated electrostatic netting were placed either towards the top or bottom openings, and other modifications were exposed to An. arabiensis under the semifield system at Ifakara Health Institute (IHI). Each night, a total of 100 starved female, 3–7-day-old, semifield reared An. arabiensis mosquitoes were released, collected the next morning (alive or dead), counted, and recorded. Live mosquitoes were maintained in the semifield insectary and monitored for 24 hours mortality. Each treatment combination of the POHD was tested in three replicates. Overall, the results indicated that the proportion of mosquitoes attracted to and killed in the POHD varied with position of attractants and killing agent (bendiocarb). The POHD with bottom placed attractants and bendiocarb attracted and killed higher proportion of mosquitoes compared to the POHD with top placed attractants and bendiocarb. The highest mortalities were observed when the POHD was baited with a combination of attractive blends and CO2. Moreover, the residual activity of attractive blends applied inside POHD varied with type and formulation of attractive blend. The POHD packed with Mbita and Ifakara blend in microencapsulated pellets (granules) attracted higher proportion of mosquitoes than that baited with soaked nylon-strip formulation of either blends. Interestingly, POHD baited with Mbita blend in microencapsulated pellets (granules) formulation attracted and killed higher proportion of mosquitoes (>90%) than that baited with Ifakara blend even 9 months after application. Conclusively, the POHD remained effective for a relatively longer period of time when baited with bottom placed synthetic blends and CO2 combination, thus warranting further trials under real life situations.

scholarly journals Anopheles arabiensis and Anopheles funestus s.s. biting pattern in Dielmo, an area of low level exposure to malaria vectors.

2020 ◽  
Author(s):  
Souleymane Doucoure ◽  
Omar Thiaw ◽  
Amélé N. Wotodjo ◽  
Charles Bouganali ◽  
Nafissatou Diagne ◽  
...  
Keyword(s):  
Malaria Transmission ◽  
Anopheles Funestus ◽  
Molecular Techniques ◽  
Malaria Vectors ◽  
Bed Nets ◽  
Low Level ◽  
Biting Rate ◽  
Outdoor Biting ◽  
Night And Day ◽  
Biting Behaviour

Abstract Background: In Dielmo, Senegal, the widespread use of long lasting insecticidal nets has decreased both the incidence of malaria and the density of the anopheles population. However, persistent low-level malaria transmission may hamper efforts to eliminate the disease. Therefore, continuous monitoring of the vector population is needed in order to improve knowledge of anopheles biting behaviour and to readjust control interventions.Methods: In 2015, anopheles were collected every month for a whole year and each specimen was identified using morphological and molecular techniques. The biting pattern of each species was analysed according to night (7pm–7am) and day (7am–11am) periods, the place of biting and the season. The ELISA CSP technique was used to evaluate the entomological inoculation rate (EIR).Results: An. arabiensis and An. funestus s.s. were found to be the main vectors biting human in Dielmo. Overall, the biting rate was low, at 3.84bites per night (bpn) and 1.27 bites per day (bpd), respectively. The EIR was 2.51 and 5.03 infected bites per year during the night and day, respectively. During the night, the An. arabiensis and An. funestus biting rate was 1.81 bpn and 1.71 bpn, respectively (p=0.80). During daylight hours, their aggressiveness decreased to 0.51 bpd and 0.73 bpd for An. arabiensis and An. funestus, respectively (p=0.30). During the night, depending on the seasons, only An. funestus displayed a significant outdoor biting behaviour both in the rainy and dry seasons, while during the day, no specific trend of indoor or outdoor biting was observed, regardless of the season for both vectors.Conclusion: This study highlighted low level anopheles nocturnal and diurnal biting and the associated risk of malaria transmission. It showed also the influence of the season on the indoor and outdoor biting pattern, indicating that the human population could be exposed all year round to a low level of anopheles bites. Control programs should increase awareness of the use of bed-nets throughout the year, particularly shortly after dawn when people are still indoors.

scholarly journals Effect of bendiocarb based (Ficam® 80% WP) Indoor Residual Spraying on feeding patterns from malaria vectors in Burkina Faso, West Africa.

2020 ◽  
Author(s):  
Sawdetuo Aristide HIEN ◽  
Dieudonné Diloma Soma ◽  
Simon Pengwende Sawadogo ◽  
Serge Bèwadéyir Poda ◽  
Moussa Namountougou ◽  
...  
Keyword(s):  
Burkina Faso ◽  
Anopheles Gambiae ◽  
Malaria Transmission ◽  
Malaria Vector ◽  
Indoor Residual Spraying ◽  
Transmission Risk ◽  
Malaria Vectors ◽  
Anopheles Coluzzii ◽  
Transmission Season ◽  
Density Methods

Abstract Background The fight against vector is essential in malaria prevention strategies in several endemic countries in Africa. In Burkina Faso, malaria transmission is seasonal in most parts of country, so a single round of spraying should provide effective protection against malaria, provided the insecticide remains effective over the entire malaria transmission season. The outcomes of indoor residual spraying towards curtailing malaria transmission are firstly to decrease the life span of vector mosquitoes and also to reduce the malaria vectors density. Methods CDC light trap and early morning collections by pyrethrum spray catches were performed monthly to determine the change in malaria vector indices in sprayed (Diebougou) and unsprayed sites (Dano). The female’s malaria vectors collected by both methods were used to determine their blood feeding, biting and sporozoites rate and malaria transmission risk estimated by entomological inoculation rate. Results Anopheles gambiae complex composed to Anopheles gambiae, Anopheles coluzzii and Anopheles arabiensis were present throughout the transmission season, but An. gambiae was the predominant species collected (P =0.0005), comprising 88% of the total collected and the most infected species. Malaria vectors densities were significantly lower in sprayed villages (n=4,303) compared with unsprayed villages (n=12,569) during post-spraying period (P = 0.0012). In addition, mean human biting rate of An. gambiae sl and An . funestus ss were significantly lower in sprayed areas compared to unsprayed areas (P<0.05). Overall, malaria vector transmission risk was significant lower in villages which received IRS (P=0.0001) whatever the malaria vectors species ( An. gambiae sl and An. funestus ss). Conclusions The results showed that in the sprayed area (Diebougou), vector densities, human biting rates and malaria transmission risks were very lower than unsprayed areas (Dano). The findings also showed a change in vector behavior especially within An. funestus which became more zoophagic following IRS. The indoor residual spraying could be recommanded as control tool in areas where malaria transmission occured a given period of year.

scholarly journals Comparative assessment of insecticide resistance phenotypes in two major malaria vectors, Anopheles funestus and Anopheles arabiensis in south-eastern Tanzania

2020 ◽  
Vol 19 (1) ◽  
Author(s):  
Polius G. Pinda ◽  
Claudia Eichenberger ◽  
Halfan S. Ngowo ◽  
Dickson S. Msaky ◽  
Said Abbasi ◽  
...  
Keyword(s):  
Insecticide Resistance ◽  
Malaria Transmission ◽  
Anopheles Arabiensis ◽  
Pyrethroid Resistance ◽  
Anopheles Funestus ◽  
Indoor Residual Spraying ◽  
Sub Saharan Africa ◽  
World Health ◽  
Malaria Vectors ◽  
South Eastern

Abstract Background Long-lasting insecticide-treated nets (LLINs) and indoor residual spraying (IRS) have greatly reduced malaria transmission in sub-Saharan Africa, but are threatened by insecticide resistance. In south-eastern Tanzania, pyrethroid-resistant Anopheles funestus are now implicated in > 80% of malaria infections, even in villages where the species occurs at lower densities than the other vector, Anopheles arabiensis. This study compared the insecticide resistance phenotypes between the two malaria vectors in an area where pyrethroid-LLINs are widely used. Methods The study used the World Health Organization (WHO) assays with 1×, 5× and 10× insecticide doses to assess levels of resistance, followed by synergist bioassays to understand possible mechanisms of the observed resistance phenotypes. The tests involved adult mosquitoes collected from three villages across two districts in south-eastern Tanzania and included four insecticide classes. Findings At baseline doses (1×), both species were resistant to the two candidate pyrethroids (permethrin and deltamethrin), but susceptible to the organophosphate (pirimiphos-methyl). Anopheles funestus, but not An. arabiensis was also resistant to the carbamate (bendiocarb). Both species were resistant to DDT in all villages except in one village where An. arabiensis was susceptible. Anopheles funestus showed strong resistance to pyrethroids, surviving the 5× and 10× doses, while An. arabiensis reverted to susceptibility at the 5× dose. Pre-exposure to the synergist, piperonyl butoxide (PBO), enhanced the potency of the pyrethroids against both species and resulted in full susceptibility of An. arabiensis (> 98% mortality). However, for An. funestus from two villages, permethrin-associated mortalities after pre-exposure to PBO only exceeded 90% but not 98%. Conclusions In south-eastern Tanzania, where An. funestus dominates malaria transmission, the species also has much stronger resistance to pyrethroids than its counterpart, An. arabiensis, and can survive more classes of insecticides. The pyrethroid resistance in both species appears to be mostly metabolic and may be partially addressed using synergists, e.g. PBO. These findings may explain the continued persistence and dominance of An. funestus despite widespread use of pyrethroid-treated LLINs, and inform new intervention choices for such settings. In short and medium-term, these may include PBO-based LLINs or improved IRS with compounds to which the vectors are still susceptible.

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