Reduced human-biting preferences of the African malaria vectors Anopheles arabiensis and Anopheles gambiae in an urban context: controlled, competitive host-preference experiments in Tanzania

Abstract BackgroundHost preference is a critical determinant of human exposure to vector-borne infections and the impact of vector control interventions. Widespread use of long-lasting insecticide-treated nets (LLINs) and indoor residual spraying (IRS) across sub-Saharan Africa, which protect humans against mosquitoes, may select for altered host preference traits of malaria vectors over the long term. Here, the host preferences of Anopheles arabiensis and Anopheles gambiae sensu stricto (s.s.) were experimentally assessed in the field, using direct host-preference assays in two distinct ecological settings in Tanzania.MethodsEight Ifakara Tent Trap (ITT), four baited with humans and four with bovine calves, were simultaneously used to catch malaria vectors in open field sites in urban and rural Tanzania. The numbers of mosquitoes collected in human-baited traps versus calf-baited traps were used to estimate human feeding preference for each site's vector species. ResultsThe estimated proportion [95% confidence interval (CI)] of mosquitoes attacking humans rather than cattle was 0.60 [0.40, 0.77] for An. arabiensis in the rural setting and 0.61 [0.32, 0.85] for An. gambiae s.s. in the urban setting, indicating no preference for either host in both cases (P=0.32 and 0.46, respectively) and no difference in preference between the two (Odds Ratio (OR) [95%] = 0.95 [0.30, 3.01], P=0.924). However, only a quarter of An. arabiensis in the urban setting attacked humans (0.25 [0.09, 0.53]), indicating a preference for cattle that approached significance (P=0.08). Indeed, urban An. arabiensis were less likely to attack humans rather than cattle when compared to the same species in the rural setting (OR [95%] = 0.21 [0.05, 0.91], P =0.037). ConclusionUrban An. arabiensis had a stronger preference for cattle than the rural population and urban An. gambiae s.s. showed no clear preference for either humans or cattle. In the urban setting, both species exhibited stronger tendencies to attack cattle than previous studies of the same species in rural contexts. Cattle keeping may, therefore, particularly limit the impact of human-targeted vector control interventions in Dar es Salaam and perhaps in other African towns and cities.

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Reduced human-biting preferences of the African malaria vectors Anopheles arabiensis and Anopheles gambiae in an urban context: controlled, competitive host-preference experiments in Tanzania

Malaria Journal ◽

10.1186/s12936-020-03495-z ◽

2020 ◽

Vol 19 (1) ◽

Author(s):

Yeromin P. Mlacha ◽

Prosper P. Chaki ◽

Athuman Muhili ◽

Dennis J. Massue ◽

Marcel Tanner ◽

...

Keyword(s):

Vector Control ◽

Anopheles Gambiae ◽

Anopheles Arabiensis ◽

Host Preference ◽

Urban Setting ◽

Sub Saharan Africa ◽

Rural Setting ◽

Malaria Vectors ◽

Baited Traps ◽

The Impact

Abstract Background Host preference is a critical determinant of human exposure to vector-borne infections and the impact of vector control interventions. Widespread use of long-lasting insecticide-treated nets (LLINs) and indoor residual spraying (IRS) across sub-Saharan Africa, which protect humans against mosquitoes, may select for altered host preference traits of malaria vectors over the long term. Here, the host preferences of Anopheles arabiensis and Anopheles gambiae sensu stricto (s.s.) were experimentally assessed in the field, using direct host-preference assays in two distinct ecological settings in Tanzania. Methods Eight Ifakara Tent Trap (ITT), four baited with humans and four with bovine calves, were simultaneously used to catch malaria vectors in open field sites in urban and rural Tanzania. The numbers of mosquitoes collected in human-baited traps versus calf-baited traps were used to estimate human feeding preference for each site's vector species. Results The estimated proportion [95% confidence interval (CI)] of mosquitoes attacking humans rather than cattle was 0.60 [0.40, 0.77] for An. arabiensis in the rural setting and 0.61 [0.32, 0.85] for An. gambiae s.s. in the urban setting, indicating no preference for either host in both cases (P = 0.32 and 0.46, respectively) and no difference in preference between the two (Odds Ratio (OR) [95%] = 0.95 [0.30, 3.01], P = 0.924). However, only a quarter of An. arabiensis in the urban setting attacked humans (0.25 [0.09, 0.53]), indicating a preference for cattle that approached significance (P = 0.08). Indeed, urban An. arabiensis were less likely to attack humans rather than cattle when compared to the same species in the rural setting (OR [95%] = 0.21 [0.05, 0.91], P = 0.037). Conclusion Urban An. arabiensis had a stronger preference for cattle than the rural population and urban An. gambiae s.s. showed no clear preference for either humans or cattle. In the urban setting, both species exhibited stronger tendencies to attack cattle than previous studies of the same species in rural contexts. Cattle keeping may, therefore, particularly limit the impact of human-targeted vector control interventions in Dar es Salaam and perhaps in other African towns and cities.

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Reduced human-biting preferences of the African malaria vectors Anopheles arabiensis and Anopheles gambiae in an urban context: Controlled, competitive host-preference experiments in Tanzania

10.21203/rs.3.rs-64353/v2 ◽

2020 ◽

Author(s):

Yeromin P Mlacha ◽

Prosper P. Chaki ◽

Athuman Muhili ◽

Dennis J. Massue ◽

Marcel Tanner ◽

...

Keyword(s):

Vector Control ◽

Anopheles Gambiae ◽

Anopheles Arabiensis ◽

Host Preference ◽

Urban Setting ◽

Sub Saharan Africa ◽

Rural Setting ◽

Malaria Vectors ◽

Baited Traps ◽

The Impact

Abstract Background: Host preference is a critical determinant of human exposure to vector-borne infections and the impact of vector control interventions. Widespread use of long-lasting insecticide treated nets (LLINs) and indoor residual spraying (IRS) across sub-Saharan Africa, which protect humans against mosquitoes, may select for altered host preference traits of malaria vectors over the long term. Here, the host preferences of Anopheles arabiensis and Anopheles gambiae sensu stricto were experimentally assessed in the field, using direct host-preference assays in two distinct ecological settings in Tanzania.Methods: Eight Ifakara Tent Trap (ITT), four baited with humans and four with bovine calves, were simultaneously used to catch malaria vectors in open field sites in urban and rural Tanzania. The numbers of mosquitoes collected in human-baited traps versus calf-baited traps were used to estimate human feeding preference for each site's vector species.Results: The estimated proportion [95% confidence interval (CI)] of mosquitoes attacking humans rather than cattle was 0.60 [0.40, 0.77] for An. arabiensis in the rural setting and 0.61 [0.32, 0.85] for An. gambiae s.s. in the urban setting, indicating no preference for either host in both cases (P=0.32 and 0.46, respectively) and no difference in preference between the two (Odds Ratio (OR) [95%] = 0.95 [0.30, 3.01], P=0.924). However, only a quarter of An. arabiensis in the urban setting attacked humans (0.25 [0.09, 0.53]), indicating a preference for cattle that approached significance (P=0.08). Indeed, urban An. arabiensis were less likely to attack humans rather than cattle when compared to the same species in the rural setting (OR [95%] = 0.21 [0.05, 0.91], P =0.037).Conclusion. Urban An. arabiensis had a stronger preference for cattle than the rural population and urban An. gambiae s.s. showed no clear preference for either humans or cattle. In the urban setting, both species exhibited stronger tendencies to attack cattle than previous studies of the same species in rural contexts. Cattle keeping may, therefore, particularly limit the impact of human-targeted vector control interventions in Dar es Salaam and perhaps in other African towns and cities.

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Reduced human-biting preferences by the African malaria vectors Anopheles arabiensis and Anopheles gambiae in an urban context: Controlled, competitive host-preference experiments in Tanzania

10.21203/rs.3.rs-64353/v1 ◽

2020 ◽

Author(s):

Yeromin P Mlacha ◽

Prosper P. Chaki ◽

Athuman Muhili ◽

Dennis J. Massue ◽

Marcel Tanner ◽

...

Keyword(s):

Anopheles Gambiae ◽

Anopheles Arabiensis ◽

Host Preference ◽

Indoor Residual Spraying ◽

Urban Setting ◽

Sub Saharan Africa ◽

Rural Setting ◽

Malaria Vectors ◽

Baited Traps ◽

The Impact

Abstract BackgroundHost preference is a critical determinant of human exposure to vector-borne infections and also the impact of interventions. Widespread use of long-lasting insecticides treated nets (LLINs) and, indoor residual spraying (IRS) across sub-Saharan Africa, which protect humans against mosquitoes, may select for altered host preference traits of malaria vectors over the long term. Here, the host preferences of Anopheles arabiensis and Anopheles gambiae sensu stricto was experimentally assessed in the field, using direct host-preference assays in two distinct ecological settings in Tanzania. MethodsEight Ifakara Tent Trap (ITT), half of them baited with humans or bovine calves were simultaneously used to catch malaria vectors in open field sites urban and rural Tanzania. The numbers of mosquitoes collected in human-baited traps versus calf-baited traps were used to estimate human feeding preference of each malaria vector species present at each site. ResultsThe estimated proportion [95% confidence interval (CI)] of mosquitoes attacking humans rather than cattle was 0.60 [0.40, 0.77] for An. arabiensis in the rural setting and 0.61 [0.32, 0.85] for An. gambiae in the urban setting, indicating no preference for either host in both cases (P=0.32 and 0.46, respectively) and no difference in preference between the two (Odds Ratio (OR) [95%] = 0.95 [0.30, 3.01], P=0.924). However, only a quarter of An. arabiensis in the urban setting attacked humans (0.25 [0.09, 0.53]), indicating a preference for cattle that approached significance (P=0.08). Indeed, urban An. arabiensis were less likely to attack humans rather than cattle when compared to the same species in the rural setting (OR [95%] = 0.21 [0.05, 0.91], P =0.037). ConclusionUrban An. arabiensis had a stronger preference for cattle than the rural population in this or previous studies, all of which reported similar traits for this species in rural contexts. Furthermore, the urban An. gambiae assessed here had a weaker preference for humans over cattle than reported by previous studies of the same species in rural contexts. Cattle keeping may therefore particularly limit the impact of human-targeted vector control interventions in Dar es Salaam and perhaps in other African towns and cities.

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A pyrethroïd-treated bed net increases host attractiveness for Anopheles gambiae s.s. carrying the kdr allele in a dual-choice olfactometer

10.1101/077552 ◽

2016 ◽

Cited By ~ 1

Author(s):

Angélique Porciani ◽

Malal Diop ◽

Nicolas Moiroux ◽

Tatiana Kadoke-Lambi ◽

Anna Cohuet ◽

...

Keyword(s):

Insecticide Resistance ◽

Anopheles Gambiae ◽

Sub Saharan Africa ◽

Malaria Vectors ◽

Malaria Vector Control ◽

Anopheles Gambiae S.S ◽

Host Seeking ◽

Seeking Behavior ◽

Sub Saharan ◽

The Impact

AbstractThe use of long lasting insecticide nets (LLINs) treated with pyrethroïd is known for its major contribution in malaria control. However, LLINs are suspected to induce behavioral changes in malaria vectors, which may in turn drastically affect their efficacy against Plasmodium sp. transmission. In sub Saharan Africa, where malaria imposes the heaviest burden, the main malaria vectors are widely resistant to pyrethroïds, the insecticide family used on LLINs, which also threatens LLIN efficiency. There is therefore a crucial need for deciphering how insecticide-impregnated materials might affect the host-seeking behavior of malaria vectors in regards to insecticide resistance. In this study, we explored the impact of permethrin-impregnated net on the host attractiveness for Anopheles gambiae mosquitoes, either susceptible to insecticides, or carrying the insecticide resistance conferring allele kdr. Groups of female mosquitoes were released in a dual-choice olfactometer and their movements towards an attractive odor source (a rabbit) protected by insecticide-treated (ITN) or untreated nets (UTN) were monitored. Kdr homozygous mosquitoes, resistant to insecticides, were more attracted by a host behind an ITN than an UTN, while the presence of insecticide on the net did not affect the choice of susceptible mosquitoes. These results suggest that permethrin-impregnated net is detectable by malaria vectors and that the kdr mutation impacts their response to a LLIN protected host. We discuss the implication of these results for malaria vector control.

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Resting Behavior of Malaria Vectors in Ghana and Its Implication on Vector Control.

10.21203/rs.3.rs-1200487/v1 ◽

2022 ◽

Author(s):

Akua Obeng Forson ◽

Isaac A. Hinne ◽

Shittu B. Dhikrullahi ◽

Isaac Kwame Sr ◽

Abdul Rahim Mohammed ◽

...

Keyword(s):

Vector Control ◽

Anopheles Gambiae ◽

Blood Meal ◽

Indoor Residual Spraying ◽

Sub Saharan Africa ◽

Malaria Vectors ◽

Resistance Mutations ◽

Sub Saharan ◽

Outdoor Resting ◽

Resting Behavior

Abstract Background: In Sub-Saharan Africa, there is widespread use of long-lasting insecticidal nets (LLINs) and Indoor residual spraying (IRS) to help control the density of malaria vectors and decrease the incidence of malaria in communities. An understanding of the interactions between increased insecticide use and resting behaviour patterns of malaria mosquitoes is important for an effective vector control programme. This study was carried out to investigate the resting behavior, host preference and infection with Plasmodium falciparum of malaria vectors in Ghana in the context of increasing insecticide resistance in malaria vectors in sub-saharan Africa.Methods: Indoor and outdoor resting Anopheline mosquitoes were sampled during the dry and rainy seasons in five sites that were in 3 ecological landscapes [Sahel savannah (Kpalsogou, Pagaza, Libga), Coastal savannah (Anyakpor) and Forest (Konongo) zones] using pyrethrum spray catches (PSC), mechanical aspiration (Prokopack) for indoor collections, pit shelter and Prokopack for outdoor collections. PCR based molecular diagnostics were used to determine mosquito speciation, genotype for knockdown resistance mutations (L1014S and L1014F), G119S Ace-1 mutation, specific host blood meal origins and sporozoite infection in field collected mosquitoes.Results: Anopheles gambiae s. l. was the predominant species (89.95%, n = 1,718), followed by An. rufipes (8.48%, n=162), and An. funestus s. l. (1.57%, n = 30). Sibling species of the Anopheles gambiae revealed An. coluzzii accounted for 63% (95% CI: 57.10 – 68.91), followed by An. gambiae s. s [27% (95% CI: 21.66 – 32.55)], and An. arabiensis [9% (95% CI: 6.22 – 13.57)]. The mean resting density of An. gambiae s. l. was higher outdoors (79.63%; 1,368/1,718) than indoors (20.37%; 350/1,718) (z = -4.815, p< 0.0001). The kdr west L1014F and the Ace-1 mutations were highest in indoor resting An. coluzzii and An. gambiae in the sahel-savannah sites compared to the forest and coastal savannah sites. Overall, the blood meal analyses revealed a large proportion of the malaria vectors preferred feeding on humans (70.2 %) than animals (29.8%) in all sites. The sporozoite rates was only detected in indoor resting An. coluzzii from the sahel savannah (5.0%) and forest (2.5%) zones.Conclusion: The study reports high outdoor resting densities of An. gambiae and An. coluzzii with high kdr west mutation frequencies, and persistence of malaria transmission indoors despite the use of LLINs and IRS. Continuous monitoring of changes in resting behavior of mosquitoes and implementation of complementary malaria control interventions are needed to target outdoor resting Anopheles mosquitoes in Ghana.

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Insecticide resistance status of Anopheles arabiensis in irrigated and non-irrigated areas in western Kenya

Parasites & Vectors ◽

10.1186/s13071-021-04833-z ◽

2021 ◽

Vol 14 (1) ◽

Author(s):

Pauline Winnie Orondo ◽

Steven G. Nyanjom ◽

Harrysone Atieli ◽

John Githure ◽

Benyl M. Ondeto ◽

...

Keyword(s):

Insecticide Resistance ◽

Vector Control ◽

Anopheles Arabiensis ◽

Crop Protection ◽

Indoor Residual Spraying ◽

Malaria Vectors ◽

Western Kenya ◽

Animal Protection ◽

Selection Of ◽

Selection Of Resistance

Abstract Background Malaria control in Kenya is based on case management and vector control using long-lasting insecticidal nets (LLINs) and indoor residual spraying (IRS). However, the development of insecticide resistance compromises the effectiveness of insecticide-based vector control programs. The use of pesticides for agricultural purposes has been implicated as one of the sources driving the selection of resistance. The current study was undertaken to assess the status and mechanism of insecticide resistance in malaria vectors in irrigated and non-irrigated areas with varying agrochemical use in western Kenya. Methods The study was carried out in 2018–2019 in Homa Bay County, western Kenya. The bioassay was performed on adults reared from larvae collected from irrigated and non-irrigated fields in order to assess the susceptibility of malaria vectors to different classes of insecticides following the standard WHO guidelines. Characterization of knockdown resistance (kdr) and acetylcholinesterase-inhibiting enzyme/angiotensin-converting enzyme (Ace-1) mutations within Anopheles gambiae s.l. species was performed using the polymerase chain reaction (PCR) method. To determine the agricultural and public health insecticide usage pattern, a questionnaire was administered to farmers, households, and veterinary officers in the study area. Results Anopheles arabiensis was the predominant species in the irrigated (100%, n = 154) area and the dominant species in the non-irrigated areas (97.5%, n = 162), the rest being An. gambiae sensu stricto. In 2018, Anopheles arabiensis in the irrigated region were susceptible to all insecticides tested, while in the non-irrigated region reduced mortality was observed (84%) against deltamethrin. In 2019, phenotypic mortality was decreased (97.8–84% to 83.3–78.2%). In contrast, high mortality from malathion (100%), DDT (98.98%), and piperonyl butoxide (PBO)-deltamethrin (100%) was observed. Molecular analysis of the vectors from the irrigated and non-irrigated areas revealed low levels of leucine-serine/phenylalanine substitution at position 1014 (L1014S/L1014F), with mutation frequencies of 1–16%, and low-frequency mutation in the Ace-1R gene (0.7%). In addition to very high coverage of LLINs impregnated with pyrethroids and IRS with organophosphate insecticides, pyrethroids were the predominant chemical class of pesticides used for crop and animal protection. Conclusion Anopheles arabiensis from irrigated areas showed increased phenotypic resistance, and the intensive use of pesticides for crop protection in this region may have contributed to the selection of resistance genes observed. The susceptibility of these malaria vectors to organophosphates and PBO synergists in pyrethroids offers a promising future for IRS and insecticide-treated net-based vector control interventions. These findings emphasize the need for integrated vector control strategies, with particular attention to agricultural practices to mitigate mosquito resistance to insecticides. Graphic abstract

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The impact of transfluthrin on the spatial repellency of the primary malaria mosquito vectors in Vietnam: Anopheles dirus and Anopheles minimus

Malaria Journal ◽

10.1186/s12936-019-3092-4 ◽

2020 ◽

Vol 19 (1) ◽

Cited By ~ 1

Author(s):

Nicholas J. Martin ◽

Vu S. Nam ◽

Andrew A. Lover ◽

Tran V. Phong ◽

Tran C. Tu ◽

...

Keyword(s):

Vector Control ◽

Large Scale ◽

Limit Of Detection ◽

Malaria Vectors ◽

Adult Mosquito ◽

Anopheles Dirus ◽

Anopheles Minimus ◽

Control Programmes ◽

The Impact ◽

Spatial Repellency

Abstract Background The complexity of mosquito-borne diseases poses a major challenge to global health efforts to mitigate their impact on people residing in sub-tropical and tropical regions, to travellers and deployed military personnel. To supplement drug- and vaccine-based disease control programmes, other strategies are urgently needed, including the direct control of disease vectors. Modern vector control research generally focuses on identifying novel active ingredients and/or innovative methods to reduce human-mosquito interactions. These efforts include the evaluation of spatial repellents, which are compounds capable of altering mosquito feeding behaviour without direct contact with the chemical source. Methods This project examined the impact of airborne transfluthrin from impregnated textile materials on two important malaria vectors, Anopheles dirus and Anopheles minimus. Repellency was measured by movement within taxis cages within a semi-field environment at the National Institute of Hygiene and Epidemiology in Hanoi, Vietnam. Knockdown and mortality were measured in adult mosquito bioassay cages. Metered-volume air samples were collected at a sub-set of points in the mosquito exposure trial. Results Significant differences in knockdown/mortality were observed along a gradient from the exposure source with higher rates of knockdown/mortality at 2 m and 4 m when compared with the furthest distance (16 m). Knockdown/mortality was also greater at floor level and 1.5 m when compared to 3 m above the floor. Repellency was not significantly different except when comparing 2 m and 16 m taxis cages. Importantly, the two species reacted differently to transfluthrin, with An. minimus being more susceptible to knockdown and mortality. The measured concentrations of airborne transfluthrin ranged from below the limit of detection to 1.32 ng/L, however there were a limited number of evaluable samples complicating interpretation of these results. Conclusions This study, measuring repellency, knockdown and mortality in two malaria vectors in Vietnam demonstrates that both species are sensitive to airborne transfluthrin. The differences in magnitude of response between the two species requires further study before use in large-scale vector control programmes to delineate how spatial repellency would impact the development of insecticide resistance and the disruption of biting behaviour.

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Impact of insecticide resistance in Anopheles arabiensis on malaria incidence and prevalence in Sudan and the costs of mitigation

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1713814114 ◽

2017 ◽

Vol 114 (52) ◽

pp. E11267-E11275 ◽

Cited By ~ 12

Author(s):

Hmooda Toto Kafy ◽

Bashir Adam Ismail ◽

Abraham Peter Mnzava ◽

Jonathan Lines ◽

Mogahid Shiekh Eldin Abdin ◽

...

Keyword(s):

Insecticide Resistance ◽

Pyrethroid Resistance ◽

Malaria Incidence ◽

Disease Incidence ◽

Indoor Residual Spraying ◽

Sub Saharan Africa ◽

Malaria Vectors ◽

Incidence And Mortality ◽

Additional Protection ◽

The Impact

Insecticide-based interventions have contributed to ∼78% of the reduction in the malaria burden in sub-Saharan Africa since 2000. Insecticide resistance in malaria vectors could presage a catastrophic rebound in disease incidence and mortality. A major impediment to the implementation of insecticide resistance management strategies is that evidence of the impact of resistance on malaria disease burden is limited. A cluster randomized trial was conducted in Sudan with pyrethroid-resistant and carbamate-susceptible malaria vectors. Clusters were randomly allocated to receive either long-lasting insecticidal nets (LLINs) alone or LLINs in combination with indoor residual spraying (IRS) with a pyrethroid (deltamethrin) insecticide in the first year and a carbamate (bendiocarb) insecticide in the two subsequent years. Malaria incidence was monitored for 3 y through active case detection in cohorts of children aged 1 to <10 y. When deltamethrin was used for IRS, incidence rates in the LLIN + IRS arm and the LLIN-only arm were similar, with the IRS providing no additional protection [incidence rate ratio (IRR) = 1.0 (95% confidence interval [CI]: 0.36–3.0; P = 0.96)]. When bendiocarb was used for IRS, there was some evidence of additional protection [interaction IRR = 0.55 (95% CI: 0.40–0.76; P < 0.001)]. In conclusion, pyrethroid resistance may have had an impact on pyrethroid-based IRS. The study was not designed to assess whether resistance had an impact on LLINs. These data alone should not be used as the basis for any policy change in vector control interventions.

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Bionomics of Anopheles Arabiensis from Mamfene in KwaZulu-Natal (South Africa): An Area of High Malaria Transmission in the Province

10.21203/rs.3.rs-52165/v1 ◽

2020 ◽

Author(s):

Rajendra Maharaj ◽

Vishan Lakan ◽

Kiash Maharaj

Keyword(s):

South Africa ◽

Vector Control ◽

Anopheles Arabiensis ◽

Mosquito Control ◽

Sex Ratios ◽

Adult Mosquito ◽

Mosquito Vector ◽

Larval Control ◽

Kwazulu Natal ◽

The Impact

Abstract Background: Although great strides have been made in controlling malaria, the disease is of significant public health importance. Historically, efforts to control the vector has concentrated on adult vector control targeting the female Anopheles mosquitoes. As there is now a focus on eliminating residual malaria from KwaZulu-Natal, new strategies are being investigated to increase the impact of malaria elimination strategies. Greater attention is now being given to larval control, as a complementary measure to indoor residual spraying. However, there is a large gap in knowledge of the bionomics of the larval stages of this mosquito vector of malaria in South Africa. In order to focus on both larval and adult mosquito control methods, larval development and the reproductive stages of the vector were investigated since these variables influences our ability to impact mosquito populations through larval control. This study was therefore conducted to determine the peak eruption times and the emergent sex ratios, as well as the peak egg oviposition time in order to attack the mosquito when it is at its most vulnerable and when control interventions will have the most impact.Results: Oviposition studies showed two peaks corresponding with late evening and again just before dawn. Most eggs were also laid in the first half of the night (18h00 – midnight). Most mosquitoes erupted just after sunset and the sex ratios showed that twice as many females as males emerged. Females readily took a bloodmeal after oviposition or just after erupting. Hatch rate to viable first instar larvae was 74.5%.Conclusions: The results of this study have provided information as to when interventions would be most effective in controlling mosquito populations and have provided information that highlights the value of larval control as a complementary measure to adult mosquito control. The most vulnerable stages of the female Anopheles arabiensis are when they have just emerged or when they have just oviposited. Vector control strategies should be designed to target these vulnerable stages at the breeding sites in order to have maximum impact.

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