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High resistance of Culex pipiens complex to various insecticides in the crowded area in Dar es Salaam City, Tanzania

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By Deokary Joseph Matiya a,b*, Shamim Khamis Msangi b, Mgeni Mohamed Tambwec and Felista Walafried Mwingira

Deokary Joseph Matiya

University of Dar es Salaam

Shamim Khamis Msangi

University of Dar es Salaam – Dar es Salaam University College of Education (DUCE)

Mgeni Mohamed Tambwe

Ifakara Health Institute

Felista Walafried Mwingira

University of Dar es Salaam

Abstract

The rapid spread of insecticide resistance in mosquitoes is a great challenge to the future of vector control tools. This study investigated the susceptibility status of Culex pipiens complex against pyrethroids (deltamethrin), carbamates (bendiocarb), and organophosphates (pirimiphos-methyl) in the Dar es Salaam University College of Education (DUCE) campus. Outdoor and indoor adult mosquitoes were collected using the Centre for Diseases Control Light traps (CDC–LTs), BG® sentinel trap, and Prokopack ®Aspirator. Moreover, the larvae and pupae were also collected through a 350ml standard dipper in the septic tanks around the building and reared to the adult stage. Both adult Culex mosquitoes directly collected from the field and those raised from the larval collection (2 to 5 days old) their susceptibility was tested against deltamethrin (0.05%), bendiocarb (0.1%), pirimiphos-methyl (0.25), and permethrin (0.75%). The overall mortality rate of 2880 adult Culex mosquitoes tested against all insecticides was below 50%. Whereas, reared mosquitoes were more resistant compared to adult mosquitoes directly collected from the field. Moreover, female mosquitoes were more resistant to all insecticides tested than male mosquitoes. These findings indicate that the current control strategy using insecticides might not help to reduce the abundance of Culexmosquitoes in the urban area. Also, this high insecticide resistance in Culexmosquitoes might lower the communities’ faith in the use of insecticide-treated bed nets (ITNs) for malaria vector control.

Keywords:Culexpipiens, Insecticides, Resistance, Susceptibility, Dar es Salaam

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Introduction

Culex mosquitoes are widely distributed in tropical and subtropical areas [1]. These mosquitoes are anthropophilic, live close to people, and exhibit nocturnal biting behaviour. Culexmosquitoes are found mostly in urban areas due to the presence of a large number of potential breeding sites such as polluted puddles, blocked open drains, and wet pit latrines [1]. They are major vectors of the filarial parasite Wuchereria bancrofti, West Nile Virus, Chikungunya virus, Western Equine Encephalitis virus, Eastern Equine Encephalitis Virus, Japanese Encephalitis virus and Saint Louis Encephalitis virus in South Asia, East Africa, and the Americas [2–4]. In Africa, lymphatic filariasis affects over 40 million people in sub-Saharan countries [5].

The free distribution of Insecticide-Treated Nets (ITNs) and implementation of Indoor Residual Spraying (IRS) as the control strategies against malaria have contributed to the great success of the elimination of lymphatic filariasis [6]. The insecticide classes recommended by WHO and widely used for mosquito control are pyrethroid (PY) organochlorine (OC), organophosphates (OP), and Carbamates (CA) whereas LLINs utilize only PY while IRS uses all classes of insecticides [7]. The effectiveness of mosquito interventions varies with mosquito species and their resistance status to insecticides used [8]. The development of insecticide resistance in mosquito vectors has been reported in various studies across the globe [9–13].

This rapid development of insecticide resistance in mosquitoes could impede the effectiveness of insecticide intervention strategies globally. Therefore, the regular monitoring of mosquito species composition and their status of insecticide resistance is of paramount importance for maximizing the effectiveness of these intervention tools. Vector surveillance and control are greatly concentrated in the household; however, little is known about the epidemiological importance of working places, hospitals, schools, colleges, Universities, and other overcrowded places [14]. Such areas are suggested to be conducive places where transmission of vector-borne diseases occurs as well as a large source of mosquitoes in the community [15].

In Tanzania, most insecticide resistance monitoring is based on malaria vectors (Matiya et al., 2019) due to the serious consequences of malaria in the population, and little is known about the resistance status of Cx.pipienscomplex to the various insecticides used in the control of mosquitoes. Studies on the susceptibility of Culexmosquitoes have shown a high resistance of

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Culex pipiens complex to at least one compound of all classes of insecticide used in their control except for organophosphates [16,17,3]. The Cx. pipiens complex found in most parts of Africa including Tanzania is the most anthropophilic and endophagic mosquito [1]. This behaviour of preferring to rest indoors increases their encounters with indoor insecticide-based tools such ITNs, IRS, aerosol spray, mosquito coils and fumigation used in malaria vector control which exerts selection pressure for insecticide-resistant strains.

Moreover, the larval stage of Cx. pipiens complex are well adapted to the urban organic pollutant breeding sites which might expose them to chemicals that may further be insecticide-resistant [4]. This may further increase the level of resistance to insecticide and increase their abundance in urban settings. The insecticide resistance in Cx. pipiens complex mosquitoes would enhance the transmission of vector-borne diseases as well as hinder malaria control by making people distrust ITNs and IRS in mosquito control (Fuseini et al., 2019; Matowo 2019). Therefore, the present study aimed to assess mosquito abundance and insecticide susceptibility status of Culexmosquitoes against pyrethroids (deltamethrin), carbamates (bendiocarb), and organophosphates (pirimiphos-methyl) at Dar-es-salaam University College of Education (DUCE) campus.

Material and methods Study site

The study was conducted at the Dar es Salaam University College of Education (DUCE) campus found in Temeke district in Dar es Salaam city, Tanzania. The sampling sites were TPC buildings, Science blocks, Chang’ombe secondary school, and male and female hostels, as shown on the map (Figure 1). Dar es Salaam is an urban coastal city with over 5.4 million people[19]. The city is characterized by a tropical climate with hot weather, high humidity, and annual rainfall of over 1000mm [20]. The rainfall in the area is bimodal with long rainy seasons (march-may) and short rainy seasons (October-December) [21].

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Fig.1. The study site (DUCE) Temeke Dar es Salaam (A = male hostel, B = female hostels, C = TPC building, D= Chang’ombe school, E= Science block)

Mosquito Collection

Outdoor and indoor adult mosquitoes were collected using the Centre for Diseases Control Light traps (CDC–LTs), BG® sentinel trap (baited with BG‑Lure – BGL), and Prokopack ®Aspirator. The collection of mosquitoes was done within two months between July and September 2021. Five CDC–LTs were used to trap mosquitoes in males and females inside hostels over the night (from 18:00 to 06:00 hours) whereas two Prokopack Aspirators were used to collect the mosquitoes around the buildings during morning time (from 06:00 to 09:00 hours) and early evening (from18:00 to19:00 hours). Also, two BG sentinel traps were used during the daytime (from 08:00 to 18:00 hours) to collect mosquitoes around the buildings and in shaded areas under trees. Moreover, the emptying of the mosquitoes from the BG sentinel trap and transferring them to the cages was done every two hours to reduce death occurrence due to desiccation. All collected

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mosquitoes were then kept in cages, fed through cotton wool soaked in 10% glucose solution, transported to the College laboratory and kept at room temperature (range from 25 to 30°C) before susceptibility testing. The larvae and pupae of Cx.pipienscomplex collected from the septic tanks were transported to the laboratory, then transferred into plastic basins and fed on Tetramin® fish food. The pupated larvae were put in the plastic cup which was placed in cages for adult mosquito emergence. The adult culicines mosquitoes were morphologically through identification key by Edwards, (1941)

Insecticide susceptibility bioassays

Insecticide susceptibility bioassays were performed as per WHO standard guidelines [23]. Mosquitoes were exposed to papers impregnated with the WHO-recommended discriminating concentrations of permethrin (0.75%), deltamethrin (0.05%), bendiocarb (0.1%), and pirimiphos- methyl (0.25). The control group was exposed to papers with silicone oil (pyrethroids control) and olive oil (carbamates and organophosphate control). Within the 1 hour of the exposure, knockdown (KD) was recorded after 10, 15 20, 30, 40, 50, and 60 minutes. Mosquitoes were then transferred into the holding tubes and fed on glucose solution. Mortality was scored after a 24-hour holding period, during which mosquitoes were given 10% glucose. During the experiments, male and female mosquitoes were tested separately. For each group of male and female mosquitoes, 80 mosquitoes were subjected to each insecticide, and four replicates were used in one test, each containing 20 mosquitoes. The mosquito susceptibility status was categorized according to WHO guidelines, which state that 98–100% mortality indicates full susceptibility, 90-97% suggests the possibility of resistance that needs to be confirmed and <90% indicates resistance [23].

Statistical analysis

The mortality of the mosquitoes exposed to insecticides was presented as the mean percentage mortality with 95% CI. The mosquito knockdown (KD) data were subjected to probit analysis using SPSS® software version 22 to estimate the time taken to knock down 50% (KDT50) and 95%(KDT95) of the exposed mosquitoes, respectively, as well as 95% confidence interval. The mortality data were analyzed and compared using Instat® statistical software. The output provided an estimated median of mortality, 95% confidence interval, and p-value based on the Kruskal-

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Wallis non-parametric test. Dunn’s Multiple Comparisons Test was used to compare mortality differences among sites.

Research clearance

The study protocol was reviewed and approved by the Vice Chancellor of the University of Dar es Salaam with a research permit no. DUCE-21047.

Results

A total of 10,213 mosquitoes were collected, of which 7413 were adults collected from the field and 2800 were adults raised from the larval collection around the campus breeding sites. Most of the collected mosquitoes were Cx.pipienscomplex, and very few were Aedesspecies 37 (0.004%). Therefore, due to very few species of Aedes mosquitoes, only Culex mosquitos were used in the insecticide susceptibility tests. About 2880 adult Culexmosquitoes were tested against deltamethrin, bendiocarb and pirimiphos-methyl.

The insecticide mortality rate of female and male Culex mosquitoes

A total of 1440 female Cxpipienscomplex were tested for susceptibility against three insecticides. Of these, 1200 adult mosquitoes were collected from the designated areas, and 240 were from the larval collection around the campus septic tanks. The mean mortality rate of adult mosquitoes collected across five selected sites ranged from 7.5 to 17.5% for deltamethrin, 15 to 25% for bendiocarb, and 5 to 15% for pirimiphos methyl. On the other hand, the mean mortality of adult mosquitoes from the collected larva was 5%, 13%, and 5% for deltamethrin, bendiocarb, and pirimiphos-methyl, respectively (Table 1 and Figure 2). These findings show Cx.pipienscomplex mosquitoes around DUCE are highly resistant to major insecticide compounds recommended for mosquito control.

Table 1. The Susceptibility status of female Cx. pipiens complex mosquitoes exposed to three insecticides.

TPC Deltamethrin (0.05%) 4 80 10 0 – 25
Bendiocarb (0.1%) 4 80 17.5 10 – 25
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Reared mosquito Deltamethrin (0.05%) 4 80 5 0 – 5
Bendiocarb (0.1%) 4 80 12.5 10 – 15
Pirimiphos-methyl (0.25%) 4 80 5 0 – 10

Rep = Replicates, N = number of mosquitoes tested, CI = Confidence interval

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Mortality(%)

Fig. 2. The Susceptibility status of field-caught adult female mosquitoes around DUCE compounds

On the other hand, a total of 1440 male mosquitoes were tested; of these, 1200 were adult mosquitoes collected from the selected sites and 240 adult mosquitoes emerged from the larval collection. The mean mortality rates of adult mosquitoes against three insecticides across five selected sites were 17.5- 42.5% for deltamethrin, 17.5 – 32.5% for bendiocarb, and 7.5- 37.5% for pirimiphos-methyl. The mean mortality of adult mosquitoes that emerged from the larval collection was 10%, 7.5%, and 10% for deltamethrin, bendiocarb, and pirimiphos-methyl respectively. (Table 2 and Figure 3). The results indicated that Cx. pipiens complex around the DUCE campus are highly resistant to major insecticide compounds tested in this study, which are recommended by the World Health Organization for mosquito control.

These findings have also shown that the mortality rate against deltamethrin of adult mosquitoes collected from the building was significantly higher in male mosquitoes than in females (p<0.05). The general trend in Cx.pipienscomplex mortality showed that mosquitoes raised from the larval collection were more resistant to deltamethrin, bendiocarb, and pirimiphos-methyl than adult mosquitoes collected inside and around the buildings. However, such mortality of Cx. pipienscomplex against all insecticides tested between the ones raised from larval collection and those collected inside and around the buildings was not significantly different (p>0.05).

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Table 2. The Susceptibility status of male Culexpipienscomplexmosquitoes exposed to three classes of insecticides

Reared Deltamethrin (0.05%) 4 80 10 5 – 25
mosquito Bendiocarb (0.1%) 4 80 7.5 0 -10
Pirimiphos-methyl 4 80 10 0 – 25

Rep= Replicates, N= the number of mosquitoes tested, CI = Confidence interval

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Mortality(%)

Fig. 3. The Susceptibility status of adult male mosquitoes collected around DUCE compounds

Mosquito knockdown times (KDT50 and KDT95) for female mosquitoes

The mean time required for 50% of mosquitoes to knock down (KDT50)of the adult mosquitoes collected from the selected sites when exposed to deltamethrin was shown to be elevated KDT50, ranging from 21.9 to 74.7 minutes, while the mean time required for 95% of mosquitoes to knock down (KDT95) ranged from 210.3-3963.3 minutes. However, the KDT50, when exposed to bendiocarb, ranged from 28.1 to 52.8 minutes, while its KDT95 was highly elevated and ranged from 866.8 to 11015.1 minutes. The KDT50, when exposed to pirimiphos-methyl, ranged from 44.4-176.4 minutes, while its KDT95 ranged from 1401.8-10832525.6 minutes. The KDT50 of the adult mosquitoes that emerged from the larval collection was 49.8, 35.4, and 77.4 when exposed to deltamethrin, bendiocarb, and pirimiphos-methyl, respectively, while their KDT95was 245975.3, 2116, and 3437.7, when exposed to deltamethrin, bendiocarb, and pirimiphos-methyl. This high KDT50 and KDT95 show the high insecticide resistance in females Cx.pipiensComplex in this area. The knockdown times (KDTS) of female mosquitoes exposed to three insecticides are shown in Table 3.

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Table 3. Knockdown times (KDTs) of Cx. pipiens complex female mosquitoes exposed to three insecticides

Adult
mosquitoes
raised from Deltamethrin (0.05%) 20 49.8 245975.3
collection Bendiocarb (0.1%) 20 35.4 (19.3-299.9) 2116 (271.6-5.4x 1015)
Pirimiphos-methyl (0.25%) 20 77.4(42.4-19754.5) 3437.7 (372.5-7.0×1014)

N= Number tested, KDT = Knockdown time, CI= confidence interval

Mosquito knockdown times (KDTs) for Male Mosquitoes

The KDT50 for male mosquitoes ranged from 22.7-75.0 minutes when exposed to deltamethrin, while its KDT95 ranged from 577.2-519729.6 minutes. Furthermore, when male mosquitoes were exposed to bendiocarb (0.1%), the KDT50 ranged from 21.6-70.9 while KDT95 ranged from 3395.2- 15497.2 minutes. The KDT50 when male mosquitoes were exposed to pirimiphos-methyl ranged from 25.4-61.4 while KDT95 ranged from 3395.2- 7447.5. Whereas when exposed to deltamethrin,

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the KDT50 was 39, 64.1, and 95.6 minutes for deltamethrin, bendiocarb, and pirimiphos-methyl, respectively while KDT95 was 519729.6, 15497.2, and 6395.4 minutes respectively. The knockdown times (KDT50) of male mosquitoes exposed to three insecticides at the site are shown in Table 4. This high KDT50 and KDT95 also show the high insecticide resistance in males Cx.pipiensComplex in this area.

Table 0. Knockdown times (KDTs) of Cx. pipiens complex male mosquitoes exposed to three insecticides

Adult Deltamethrin (0.05%) 20 39.0 519729.6
mosquitoes Bendiocarb (0.1%) 20 64.1 15497.2
raised from collection Pirimiphos-methyl (0.25%) 20 95.6(46.5-8.3 x109) 6395.4 (452.7-1.6 x1039)

N= Number tested, KDT = Knockdown time, CI= confidence interval

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Generally, female mosquitoes showed slow knockdown (KDT50>30min) when exposed to deltamethrin, except for mosquitoes collected from the male hostel and Chag’ombe secondary, their knockdown was faster (i.e. KDT50<30min). Similarly, female mosquitoes exposed to bendiocarb indicated slow knockdown except for mosquitoes collected from the TPC building and male hostels. In addition, female mosquitoes across all sites showed slow knockdown after exposure to pirimiphos-methyl. Conversely, male mosquitoes exposed to deltamethrin showed slow knockdown (KDT50>30) except for those collected from Chang’ombe secondary. Similarly, when exposed to bendiocarb, it showed slow knockdown except for mosquitoes collected from the TPC building and female hostel. Moreover, male mosquitoes indicated slow knockdown (KDT50>30) after being exposed to pirimiphos-methyl, except mosquitoes collected from the male hostel and chang’ombe secondary showed faster knockdown (i.e., KDT50<30). The finding showed that KDT95 for both male and female mosquitoes across all sites was high.

Discussion

The study aimed to assess the mosquito abundance, and susceptibility status against different classes of insecticides; pyrethroids (deltamethrin), carbamates (bendiocarb), and organophosphates (pirimiphos-methyl around the DUCE campus. Our findings highlighted that the abundant species of mosquito during the study were Culexspecies and were highly resistant to the tested insecticide compounds.

The male mosquitoes recorded a 2-fold higher mortality rate than female mosquitoes when exposed to deltamethrin and pirimiphos-methyl. Similarly, the mortality rate of male mosquitoes (23.75%) was higher than that of females (15.4%) when exposed to bendiocarb. The plausible explanation for male mosquitoes being more susceptible compared to females might be due to their small body sizes which makes them vulnerable to insecticides females [23]. Similar results were reported by Matowo et al. (2019), conducted in rural south-eastern Tanzania. On the other hand, in all insecticides tested mortality rate of both females and males raised from larval collection was lower compared to the mortality rate of adult mosquitoes directly collected from selected areas on campus. The reason for the high resistance of mosquitoes raised from the larval was due to homogeneous age compared to the collected adults, which have mixtures of young and older mosquitoes, of which older ones are more susceptible to insecticides [23].

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In this study, Culexmosquitoes showed slow knockdown (KDT50>30min) and (KDT95>60min) in all tested insecticides. These results mean that it took a long time for mosquitoes to be knocked down, indicating that mosquitoes around the DUCE campus are highly resistant to tested insecticides. The higher KDT in Culex mosquitos when exposed to pyrethroids was also reported in the other studies conducted in Tanzania and elsewhere in Africa and South Europe [11,12,17]. In contrast to those studies, the KDT for bendiocarb (Carbamates) and pirimiphos-methyl (organophosphate) was also very high. This high KDT of Cx. pipiens complex to bendiocarb and pirimiphos-methyl might be due to the high application of these compounds for vector-borne disease control in these populated urban areas [24].

Furthermore, the study demonstrated very low mortality of Culex mosquitoes’ to Deltamethrin, Bendiocarb insecticides, and pirimiphos-methyl at the DUCE campus. In our study the Culex mosquitoes have shown the highest resistance to pirimiphos-methyl (mortality ranges, 5-15% for females and 7.5-37.5% for males), these results are different from findings of the studies conducted in rural areas in Tanzania and Ethiopia [3,17,25] (mortality ranges, 90 -100%). The possible explanation for these discrepancies might be those insecticides are highly used in the form of an outdoor spray, and fumigation indoor aerosol spray in the control of vector-borne disease control [24].

Likewise, the current study showed that Culex mosquitoes were highly resistant to deltamethrin (mortality ranges; 7.5-17.5% for females and 17.5-42.5% for males). Similar findings were recorded by studies conducted in urban areas elsewhere in Africa and Asia (mortality ranges; 0- 48%) [4,6,26]. The high resistance of the Cx. pipiens complex mosquitoes deltamethrin might be due to the high anthropophilic (preference of bite in humans) and endophilic (resting indoor) nature which could have made them in frequent contact with indoor-based insecticide intervention (ITNs, aerosols, and coils), most of which contain pyrethroids such as deltamethrin, that are highly utilized in the urban areas [4,18]. The frequent contact with these mosquitoes with insecticides exerts high selective pressure for resistant mosquito strains.

Nonetheless, the mortality rate against deltamethrin in our study was lower than in studies conducted in rural Tanzania (mortality ranges; 8-99% for both females and males) [3], elsewhere in rural areas in African countries (mortality ranges; 63-100%) [25,27], and other studies in countries with limited usage of insecticides in Europe, America and Asia (mortality ranges; 59-

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100%) [11,28–30]. This indicates that these mosquitoes found in rural areas with small populations of insecticide-treated bed net users and areas with restricted use of insecticides, delay the development of insecticide resistance in these mosquitoes.

In addition, the study showed resistance of Culex mosquitoes to bendiocarb was also high (ranging; from 15 to 25% for females and 17.5 to 32.5% for males). This mortality was similar to the study conducted in rural areas in Tanzania (mortality ranges; 9-26%) [17] and urban areas in Cameroon (mortality ranges; 0-14.6%) [4]. On the other hand, the bendiocarb mortality in our study was lower than in the study conducted in rural areas in Tanzania (mortality ranges; 29-100%)

[3] and in the rural areas elsewhere in Africa (mortality ranges; 50-81%) [6,25,27]. Moreover, the mortality rates of these mosquitoes in the current study were lower than in a previous study conducted in urban areas of Benin (mortality was 60%) [6]. These results of high and low insecticide mortality in mosquitoes on bendiocarb exposure in urban areas of different countries indicate the heterogeneity in the preference of bendiocarb utilization for different purposes in urban areas.

The high resistance Cx. pipiens complex against all insecticides tested in the current study conducted in an urban setting could also be these mosquitoes are well adapted to the urban organic pollutants and chemical effluents from industries leaching in their breeding sites. Thus are constantly exposed to these chemicals which might further select resistant strains and worsen the insecticide resistance situation [4,31]. The significant implication of this high resistance in Culexmosquitoes in this study area is that these mosquitoes could not be controlled by the tested insecticides. The failure of insecticides to control mosquitoes might result in the emergence or resurgence of Culex mosquito-borne diseases and increased nuisance of these mosquitoes with high indoor biting rates. Moreover, the high resistance in this species of mosquitoes might also result in the community distrusting the insecticide-based tools (ITNs and coils) which are still effective in controlling malaria vectors, hence resurgence in malaria [18,32]. Therefore, it is important to mitigate this insecticide resistance situation in the Culex mosquitoes at the DUCE campus and neighbouring areas in Dar es Salaam city for the betterment health of the community.

One limitation of the current study was that it was conducted only during the dry season, hence fell short on seasonality results. It will be more fruitful to conduct the same study during the wet (rainy) followed by the dry season, this will help get more information on species composition and

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insecticide susceptibility status on different species of mosquitoes available during the rainy season. Thus, further studies are needed to establish insecticide resistance in other insecticide classes.

5. Conclusions

The current study indicates that all Culex mosquitoes collected across different sites at the DUCE campus were resistant to deltamethrin, bendiocarb, and pirimiphos-methyl. Furthermore, the mosquitoes raised from the larval collection were more resistant to insecticides than adult mosquitoes directly collected from different sites. In addition, mosquitoes were more resistant to pirimiphos-methyl than deltamethrin and bendiocarb. Furthermore, female mosquitoes were more resistant to all insecticides tested than male mosquitoes. Therefore, using the tested insecticides in this study might not reduce the abundance of these mosquitoes in urban areas in Dar es Salaam. This implies that other vector control methods such as environmental modification and reduction of mosquito breeding sources.

Declaration of Competing Interest

The authors declare that they have no competing interests.

Acknowledgements

We are grateful to Dar es University College of Education (DUCE) for permitting us to collect mosquitoes from their areas.

Authors’ contributions

DJM and FM, secured funds, designed, conceptualized, supervised the study, analyzed data and revised the manuscript. DJM and SM performed laboratory analysis and wrote the original draft. DJM, MMT and FM critically review the manuscript. All authors read and approved the final manuscript.

Funding:the research was funded by Dar es Salaam University College of Education (DUCE)

Availability of materials and data

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All the data analyzed and interpreted during this study are archived and available upon reasonable request.

References

  1. C.M. Jones, C. Machin, K. Mohammed, S. Majambere, A.S. Ali, B.O. Khatib, J. Mcha, H. Ranson, L.A. Kelly-Hope, Insecticide resistance in Culex quinquefasciatus from Zanzibar: implications for vector control programmes, Parasit. Vectors. 5 (2012) 78. https://doi.org/10.1186/1756-3305-5-78.
  2. S.L. Richards, J.A.G. Balanay, M. Fields, K. Vandock, Baseline Insecticide Susceptibility Screening Against Six Active Ingredients for Culex and Aedes (Diptera: Culicidae) Mosquitoes in the United States, J. Med. Entomol. 54 (2017) 682–695. https://doi.org/10.1093/jme/tjw231.
  3. N.S. Matowo, S. Abbasi, G. Munhenga, M. Tanner, S.A. Mapua, D. Oullo, L.L. Koekemoer,

E. Kaindoa, H.S. Ngowo, M. Coetzee, J. Utzinger, F.O. Okumu, Fine-scale spatial and temporal variations in insecticide resistance in Culex pipiens complex mosquitoes in rural south-eastern Tanzania, Parasit. Vectors. 12 (2019) 413. https://doi.org/10.1186/s13071-019- 3676-4.

  1. A. Talipouo, K. Mavridis, E. Nchoutpouen, B. Djiappi-Tchamen, E.A. Fotakis, E. Kopya, R. Bamou, S. Kekeunou, P. Awono-Ambene, V. Balabanidou, S. Balaska, C.S. Wondji, J. Vontas, C. Antonio-Nkondjio, High insecticide resistance mediated by different mechanisms in Culex quinquefasciatus populations from the city of Yaoundé, Cameroon, Sci. Rep. 11 (2021) 7322. https://doi.org/10.1038/s41598-021-86850-7.
  2. K. Deribe, D.K. Bakajika, H.M.-G. Zoure, J.O. Gyapong, D.H. Molyneux, M.P. Rebollo, African regional progress and status of the programme to eliminate lymphatic filariasis: 2000–2020, Int. Health. 13 (2020) S22–S27. https://doi.org/10.1093/inthealth/ihaa058.
  3. A. Yadouléton, K. Badirou, R. Agbanrin, H. Jöst, R. Attolou, R. Srinivasan, G. Padonou, M. Akogbéto, Insecticide resistance status in Culex quinquefasciatus in Benin, Parasit. Vectors. 8 (2015) 17. https://doi.org/10.1186/s13071-015-0638-3.
  4. WHO, Recommended insecticides for indoor residual spraying against malaria vectors, World Health Organization, Geneva, 2018. https ://www. who.int/negle cted_disea ses/vecto

18

r_ecolo gy/vecto r-contr ol/Insec ticid es_IRS_22_Septe mber_2018.pd (accessed July 18, 2019).

  1. P.G. Pinda, C. Eichenberger, H.S. Ngowo, D.S. Msaky, S. Abbasi, J. Kihonda, H. Bwanaly,

F.O. Okumu, Comparative assessment of insecticide resistance phenotypes in two major malaria vectors, Anopheles funestus and Anopheles arabiensis in south-eastern Tanzania, Malar. J. 19 (2020) 408. https://doi.org/10.1186/s12936-020-03483-3.

  1. A. Tabbabi, J. Daaboub, R.B. Cheikh, A. Laamari, M. Feriani, C. Boubaker, I.B. Jha, H.B. Cheikh, Comparison of Resistance Status to Permethrin (Pyrethroid Insecticide) in Culex pipiens pipiens (Diptera: Culicidae) Collected from Three Localities of Tunisia, J. Kans. Entomol. Soc. 91 (2018) 85–93. https://doi.org/10.2317/0022-8567-91.1.85.
  2. D.J. Matiya, A.B. Philbert, W. Kidima, J.J. Matowo, Dynamics and monitoring of insecticide resistance in malaria vectors across mainland Tanzania from 1997 to 2017: a systematic review, Malar. J. 18 (2019) 102. https://doi.org/10.1186/s12936-019-2738-6.
  3. O. Ser, H. Cetin, Investigation of Susceptibility Levels of Culex pipiens L. (Diptera: Culicidae) Populations to Synthetic Pyrethroids in Antalya Province of Turkey, J. Arthropod- Borne Dis. 13 (2019) 243–258.
  4. A.I. Omotayo, M.M. Dogara, D. Sufi, T. Shuaibu, J. Balogun, S. Dawaki, B. Muktar, K. Adeniyi, N. Garba, I. Namadi, H.A. Adam, S. Adamu, H. Abdullahi, A. Sulaiman, A.O. Oduola, High pyrethroid-resistance intensity in Culex quinquefasciatus (Say) (Diptera: Culicidae) populations from Jigawa, North-West, Nigeria, PLoS Negl. Trop. Dis. 16 (2022) e0010525. https://doi.org/10.1371/journal.pntd.0010525.
  5. I. Kura Shehu, H.B. Ahmad, I. Kayode Olayemi, D. Solomon, A. Hassan Ahmad, H. Salim, Insecticide susceptibility status in two medically important mosquito vectors, Anopheles gambiae, and Culex quinquefasciatus to three insecticides commonly used in Niger State, Nigeria, Saudi J. Biol. Sci. 30 (2023) 103524. https://doi.org/10.1016/j.sjbs.2022.103524.
  6. V.A. Olano, M.I. Matiz, A. Lenhart, L. Cabezas, S.L. Vargas, J.F. Jaramillo, D. Sarmiento,

N. Alexander, T.A. Stenström, H.J. Overgaard, Schools as Potential Risk Sites for Vector- Borne Disease Transmission: Mosquito Vectors in Rural Schools in Two Municipalities in Colombia, J. Am. Mosq. Control Assoc. 31 (2015) 212–222. https://doi.org/10.2987/moco- 31-03-212-222.1.

19

  1. C.M. Hernández-Suárez, O. Mendoza-Cano, Empirical evidence of the effect of school gathering on the dynamics of dengue epidemics, Glob. Health Action. 9 (2016) 28026. https://doi.org/10.3402/gha.v9.28026.
  2. M.A. Kulkarni, R. Malima, F.W. Mosha, S. Msangi, E. Mrema, B. Kabula, B. Lawrence, S. Kinung’hi, J. Swilla, W. Kisinza, M.E. Rau, J.E. Miller, J.A. Schellenberg, C. Maxwell, M. Rowland, S. Magesa, C. Drakeley, Efficacy of pyrethroid-treated nets against malaria vectors and nuisance-biting mosquitoes in Tanzania in areas with long-term insecticide-treated net use, Trop. Med. Int. Health. 12 (2007) 1061–1073. https://doi.org/10.1111/j.1365- 3156.2007.01883.x.
  3. B. Emidi, W.N. Kisinza, R.D. Kaaya, R. Malima, F.W. Mosha, Insecticide susceptibility status of human biting mosquitoes in Muheza, Tanzania, Tanzan. J. Health Res. 19 (2017). https://doi.org/10.4314/thrb.v19i3.9.
  4. G. Fuseini, R.N. Nguema, W.P. Phiri, O.T. Donfack, C. Cortes, M.E. Von Fricken, J.I. Meyers, I. Kleinschmidt, G.A. Garcia, C. Maas, C. Schwabe, M.A. Slotman, Increased Biting Rate of Insecticide-Resistant Culex Mosquitoes and Community Adherence to IRS for Malaria Control in Urban Malabo, Bioko Island, Equatorial Guinea, J. Med. Entomol. 56 (2019) 1071–1077. https://doi.org/10.1093/jme/tjz025.
  5. URT, NBS, The Unite Republic of Tanzania, National Bureau of Statistics – Census 2022 Results, United Republic of Tanzania, National Bureau of Statistics, Dodoma, Tazania, 2022. https://www.nbs.go.tz/nbs/takwimu/Census2022/matokeomwanzooktoba2022.pdf (accessed November 5, 2022).
  6. E.L. Ndetto, A. Matzarakis, Basic analysis of climate and urban bioclimate of Dar es Salaam, Tanzania, Theor. Appl. Climatol. 114 (2013) 213–226. https://doi.org/10.1007/s00704-012- 0828-2.
  7. T. Kabanda, Long-Term Rainfall Trends over the Tanzania Coast, Atmosphere. 9 (2018) 155. https://doi.org/10.3390/atmos9040155.
  8. F.W. Edwards, Mosquitoes of the Ethiopian Region, III Culicine Adults and Pupae, The Oxford University Press, London and Dorking, England, 1941. https://mosquito-taxonomic- inventory.myspecies.info/sites/mosquito-taxonomic- inventory.info/files/Edwards%201941.pdf (accessed April 6, 2023).
  9. WHO, WHO 2016 Testing procedure for insecticides.pdf, Geneva, Switzerland, 2016.

20

  1. C. Makungu, S. Stephen, S. Kumburu, N.J. Govella, S. Dongus, Z.J.-L. Hildon, G.F. Killeen,

C. Jones, Informing new or improved vector control tools for reducing the malaria burden in Tanzania: a qualitative exploration of perceptions of mosquitoes and methods for their control among the residents of Dar es Salaam, Malar. J. 16 (2017) 410. https://doi.org/10.1186/s12936-017-2056-9.

  1. W. Guta, E.A. Simma, D. Yewhalaw, Species composition, blood meal sources and insecticide susceptibility status of Culex mosquitoes from Jimma area, Ethiopia, Int. J. Trop. Insect Sci. 41 (2021) 533–539. https://doi.org/10.1007/s42690-020-00237-1.
  2. A.V. K, E. Pushpalatha, P.K. Srivastava, Insecticide Resistance Monitoring in Culex quinquefasciatus – the Vector of Lymphatic Filariasis, J. Commun. Dis. E-ISSN 2581-351X P-ISSN 0019-5138. 52 (2020) 61–64.
  3. A. Olatubosun, O. James, A. Taiwo, Surveillance and insecticide susceptibility status of culicine mosquitoes in selected communities utilizing long-lasting insecticidal nets in Kwara state, Nigeria, Anim. Res. Int. (2016).
  4. C. Delannay, D. Goindin, K. Kellaou, C. Ramdini, J. Gustave, A. Vega-Rúa, Multiple insecticide resistance in Culex quinquefasciatus populations from Guadeloupe (French West Indies) and associated mechanisms, PLoS ONE. 13 (2018) e0199615. https://doi.org/10.1371/journal.pone.0199615.
  5. S.L. Richards, J.A.G. Balanay, A.V. White, J. Hope, K. Vandock, B.D. Byrd, M.H. Reiskind, Insecticide Susceptibility Screening Against Culex and Aedes (Diptera: Culicidae) Mosquitoes From the United States, J. Med. Entomol. 55 (2018) 398–407. https://doi.org/10.1093/jme/tjx198.
  6. S. Vereecken, A. Vanslembrouck, I.M. Kramer, R. Müller, Phenotypic insecticide resistance status of the Culex pipiens complex: a European perspective, Parasit. Vectors. 15 (2022) 423. https://doi.org/10.1186/s13071-022-05542-x.
  7. T.E. Nkya, I. Akhouayri, W. Kisinza, J.-P. David, Impact of environment on mosquito response to pyrethroid insecticides: Facts, evidences and prospects, Insect Biochem. Mol. Biol. 43 (2013) 407–416. https://doi.org/10.1016/j.ibmb.2012.10.006.
  8. A.A. Kudom, B.A. Mensah, G. Froeschl, D. Boakye, H. Rinder, Preliminary assessment of the potential role of urbanization in the distribution of carbamate and organophosphate