Annual Report of the LaMer Project FY 2023
1. Title of the research project:
Insecticide resistance status and future insecticide choices for vector control
strategies in Bangladesh.
2. Names and affiliation of members:
1. Prof. Kozo Watanabe, Full Professor of Molecular Ecology andHealth (MEcoH) Laboratory at the Center for Marine Environmental
Studies (CMES), Ehime University, Japan.
2. Dr. Ashekul Islam, Assistant Professor and Principal Investigatorof Vector Borne Diseases Laboratory at the Department ofBiochemistry and Molecular Biology, Mawlana Bhashani Scienceand Technology University, Tangail 1902, Bangladesh.
3. Mohammad Mosleh Uddin, PhD student, Molecular Ecology andHealth (MEcoH) Laboratory at the Center for Marine Environmental
Studies (CMES), Ehime University, Japan.
4. Md. Sujan Islam, MS thesis student, Vector Borne Diseases
Laboratory at the Department of Biochemistry and MolecularBiology, Mawlana Bhashani Science and Technology University,
Tangail 1902, Bangladesh.
5. Sadia Afrin, MS thesis student, Vector Borne Diseases Laboratory
at the Department of Biochemistry and Molecular Biology, Mawlana
Bhashani Science and Technology University, Tangail 1902,
Bangladesh.
6. Maria Mehjabin Anki, MS thesis student, Vector Borne Diseases
Laboratory at the Department of Biochemistry and MolecularBiology, Mawlana Bhashani Science and Technology University,
Tangail 1902, Bangladesh.

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3. Purposes:
Monitor and analyze trends in insecticide resistance among local mosquito
populations, particularly in Culex spp. and Aedes aegypti, to inform andoptimize vector control strategies. This approach should include periodic
surveillance, resistance mechanism studies, and the evaluation of alternativecontrol methods to ensure effective and sustainable vector management.

4. Methods:

Mosquito larvae collection and rearing:
Mosquito larvae were collected from several locations in Tangail Sadar andDhaka, Bangladesh, and reared into adults at the Vector Borne Disease
Laboratory (VBDL) of Mawlana Bhashani Science and Technology University(MBSTU). The colonies were maintained independently, fed with either a 10%
sugar solution or anesthetized mice blood, following the methods previously
described by Min-Lin Zheng et al. [1].

Adulticide action under laboratory conditions:
The mosquito populations were assessed for susceptibility to Deltamethrin
and Dimefluthrin by measuring mortality rates at 30 minutes. According to
WHO and CDC guidelines, populations with mortality rates below 90% wereclassified as resistant, those with rates of 98% or higher were deemedsusceptible, and mortality rates between 90% and 97% suggested developing
resistance [2, 3].
Results:

Adulticide action using Deltamethrin:
In our study on the effectiveness of Deltamethrin and Dimefluthrin, we foundthat both Ae. aegypti and Culex spp. demonstrated resistance toDeltamethrin. At a diagnostic time (DT) of 30 minutes and using the CDCrecommended diagnostic dose of 10µg/ml per 250 ml bottle, the laboratoryreared Ae. aegypti population had a mortality rate of 61.5% at 1×concentration and 72.727% at 5× concentration (Figure 01).

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Figure 01: Susceptibility of A. aegypti by Deltamethrin
Mosquito survival past the diagnostic time (DT) suggests resistance. To
assess resistance strength, we extended observations beyond the DT.
According to CDC guidelines, the failure to achieve 100% mortality at any
dose (1×, 3×, or 5×) indicates significant resistance. Similar patterns wereobserved in wild-type Culex spp.; at a DT of 45 minutes with a dose of 10µg/ml
per 250 ml bottle, mortality was only 26.0%, and no dose reached 100%
mortality, underscoring the extensive resistance (Figure 02).

Figure 02: Susceptibility of Culex spp. by Deltamethrin

Adulticide action using Dimefluthrin:
We tested Dimefluthrin at different concentrations (2µg/ml, 4µg/ml, 6µg/ml,10µg/ml) and at higher levels (100µg/ml, 200µg/ml, 300µg/ml) similar to thosefound in commercial mosquito coils. Our data indicate that both Ae. aegypti
and Culex spp. are highly susceptible to Dimefluthrin. For Ae. aegypti, themaximum survival time was 25 minutes at the 2µg/ml dose, with knockdown
occurring before 15 minutes at higher doses (Figure 03).

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Figure 03: Susceptibility of A. aegypti by Dimefluthrin

Culex spp. showed a similar pattern, with the longest survival at 2µg/ml for
15 minutes and knockdown before 15 minutes at all higher doses (Figure 04).

Figure 04: Susceptibility of Culex spp. by Dimefluthrin
Future Challenges:
Although laboratory bioassays provide growing data on insecticide resistancein mosquito vectors, they fall short of guiding stakeholders on effective vector
control strategies. To address practical resistance, standardization at thelocal level is crucial, enabling national programs to assess the changing
efficacy of control measures over time. Therefore, assessing the real-world
impact of insecticide use requires comprehensive studies incorporating
surveillance, disease prevalence, and resistance mechanisms.
References:
1. Zheng ML, Zhang DJ, Damiens DD, Lees RS, Gilles JRL. Standard
operatingprocedures for standardized mass rearing of the dengue and chikungunya vectors
Aedes aegypti and Aedes albopictus (Diptera: Culicidae) - II - Egg storage andhatching. Parasites and Vectors. 2015;8:1–7. doi:10.1186/S13071-015-0951X/TABLES/3.
2. Al-Amin HM, Johora FT, Irish SR, Hossainey MRH, Vizcaino L, Paul KK, et al.
Insecticide resistance status of Aedes aegypti in Bangladesh. Parasit
Vectors.
2020;13. doi:10.1186/S13071-020-04503-6.
3. Al-Amin, H.M., Gyawali, N., Graham, M., Alam, M.S., Lenhart, A., Hugo,L.E.,
Rašić, G., Beebe, N.W. and Devine, G.J. (2023), Insecticide resistance compromises
the control of Aedes aegypti in Bangladesh. Pest Manag Sci, 79: 2846-2861.
https://doi.org/10.1002/ps.7462
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