Morphotype-Associated Insecticide Resistance and Genetic Variation in Aedes Aegypti Populations of Kathmandu, Nepal



Ongoing


2025 to 2027


INSTITUTE OF TROPICAL Medicine Antwerp Belgium and NHRC


Kathmandu, Lalitput, Bhaktapur


The global proliferation of Aedes aegypti, a major vector of arboviruses such as dengue, chikungunya, and Zika, has increasingly been shaped by urbanization-driven selective pressures. Notably, colour morphs within Ae. aegypti populations may reflect underlying genetic and physiological differences, including insecticide resistance mechanisms.

Historic work by Craig & Vandehey (1962) documented a variety of inherited colour mutations (e.g. white abdomen, gold mesonotum, black palps) in laboratory strains of Aedes aegypti, emphasizing their potential as phenotypic markers of genetic variation. More recently, Verna & Munstermann (2011) described morphologically distinct field-collected Ae. aegypti from the Caribbean that paralleled laboratory-characterized mutations, including the white abdomen (W) and gold mesonotum (G) variants. These traits are not merely cosmetic: they are linked to chromosomal loci that may be in linkage disequilibrium with resistance alleles (e.g. for dieldrin or malathion resistance) (Craig & Vandehey 1962). Importantly, studies on other insects, such as Diaphorina citri, have confirmed that colour morphs are associated with differences in susceptibility to insecticides, correlating with variation in cytochrome P450 expression (Tiwari et al. 2013). In mosquitoes, similar associations have been proposed but remain underexplored in field populations.

The recent synthesis by Fifer et al. (2025) outlines how traits such as insecticide resistance and host preference often evolve as exaptation’s and are tied to complex genomic architectures involving inversions, introgression, and standing variation. These can drive rapid adaptation in urban environments where ecological filters—e.g. breeding site type or microclimate—select for linked behavioural and physiological traits. Supporting this, Kramer et al. (2022) identified a sharp genomic discontinuity between lowland and highland Ae. aegypti in Nepal. Highland population from Kathmandu (1300 m) exhibited distinct allele frequencies in climate- and resistance-associated genes, suggesting a punctuated expansion by a pre-adapted lineage. Enhanced cold tolerance and resistance-linked mutations (e.g. in detoxification pathways and kdr loci) indicate the potential for persistence and further spread into cooler, highland environments (Kramer et al. 2023).

Together, these findings highlight that morphologically distinct Ae. aegypti populations in Kathmandu may reflect deeper genomic and functional divergence. Given the ecological heterogeneity of Kathmandu valley and increasing biocide and pesticide pressure, a detailed evaluation of colour morphs in relation to phenotypic and genotypic insecticide resistance is timely. Colour morphs could serve as visible proxies for adaptive differentiation, warranting their systematic phenotyping and genotyping in relation to insecticide resistance and ecological tolerance and may offer actionable insights for vector control.


General Objective 

This study aims to investigate whether distinct colour morphs of A. aegypti in the Kathmandu Valley are associated with phenotypic and genotypic insecticide resistance, and whether these morphs correspond to genetically distinct clusters identified through AI-based image analysis. Additionally, the study aims to assess how the distribution of morphotypes and resistance profiles varies across different land-use types

Specific Objectives

  1. To document and classify distinct colour morphs of Ae. aegypti using AI-assisted image analysis based on pattern, colour, and texture features.
  2. To determine insecticide susceptibility profiles of individual mosquitoes representing different morphotypes using a) CDC bottle bioassay with permethrin; b) PBO synergist testing to differentiate metabolic resistance (via P450s) from target-site resistance.
  3. To detect resistance-associated alleles (kdr mutations V1016G and F1534C) and analyse their distribution across colour morphs and morph clusters.
  4. To test whether colour morphs are predictive of phenotypic and genotypic resistance, indicating potential linkage between morphological and resistance traits.
  5. To assess whether unsupervised morph clusters derived from image-based feature extraction correspond with insecticide resistance profiles and genotypes.
  6. To evaluate whether the frequency of colour morphs and associated genetic and metabolic resistance traits varies systematically across land-use categories (e.g. urban, peri-urban, agricultural, industrial).
  7. To explore the utility of morph-based classification as a rapid proxy for insecticide resistance surveillance in diverse urban and peri-urban environments.

Identification of color morphs that are predictive of insecticide resistance (e.g. kdr mutations V1016G, F1534C), and AI-assisted classification of morphs, enabling scalable and rapid resistance surveillance. 

Mapping of resistant morphs across urban, peri-urban, and industrial land-use types in Kathmandu