Mosquito Diversity and Public Health Risk in Kerala, India: A Synthesis of a Multi-District Survey
Source: Mathiarasan, L., Natarajan, R., Aswin, A.
et al. Diversity and spatiotemporal distribution of mosquitoes (Diptera: Culicidae) with emphasis on disease vectors across agroecological areas of Kerala, India.
Sci Rep 15, 30603 (2025).
https://doi.org/10.1038/s41598-025-16357-y
Date: Received - 29 May 2025 | Accepted - 14 August 2025 | Published - 20 August 2025
Executive Summary
This document synthesizes the findings of an extensive entomological survey conducted across five agroecological districts of Kerala, India. The research reveals a remarkably diverse mosquito fauna, identifying 108 species, including 14 known disease vectors, which underscores the region's complex public health challenges. The study highlights the overwhelming predominance of Stegomyia albopicta (54.82% of all collected specimens), a highly adaptable vector for dengue and chikungunya, posing a significant and ongoing threat.
Key findings indicate that artificial, human-made habitats—such as discarded tires, plastic containers, and latex collection cups—are the primary breeding grounds, supporting greater species diversity than natural habitats and pointing to critical deficiencies in solid waste management. The Wayanad district was identified as a major biodiversity hotspot for mosquitoes, attributed to its unique ecological niches. The investigation also yielded significant scientific discoveries, including the description of a new species, Heizmannia rajagopalani, and the first regional records of several other species. The co-existence of multiple vectors for arboviruses, malaria, and filariasis creates a complex risk profile that necessitates comprehensive surveillance and targeted, ecologically-informed control strategies.
1. Overview of the Entomological Survey
The study was designed to conduct a comprehensive assessment of mosquito biodiversity, spatiotemporal distribution, and habitat preferences across diverse ecological settings in Kerala, India, a state known for its unique agro-geographical features and history of mosquito-borne disease (MBD) outbreaks.
- Objective: To evaluate mosquito species composition, spatial and temporal distribution, and ecological and habitat preferences to inform public health risk assessment and vector control strategies.
- Scope and Duration: The survey was conducted from February 2016 to September 2017 in five districts selected for their varied ecotypes:
- Wayanad (forested, high altitude)
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- Ernakulam (coastal, plantation)
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- Pathanamthitta (Western Ghats, plantation)
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- Idukki (mountainous, tea cultivation)
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- Thiruvananthapuram (capital, urban/rural/coastal)
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- Methodology: The research employed a dual sampling approach, collecting both immature (larvae, pupae) and adult mosquitoes. Immature specimens were collected from 777 habitats, while 4,021 adult mosquitoes were collected from 422 sites. Species were identified using standard morphological and taxonomic keys.
- Total Collection: A total of 12,535 mosquito specimens were collected and identified.
2. Species Composition and Abundance
The survey revealed a rich and diverse mosquito fauna, highlighting a complex ecosystem of both nuisance species and medically important vectors.
Overall Diversity
A total of 108 mosquito species belonging to 28 genera were identified. The genus Culex exhibited the highest species richness (25.0%), followed by Anopheles (12.9%) and Stegomyia (10.2%).
Dominant Species
The vast majority of collected specimens were dominated by a few highly prevalent species:
| Species | Percentage of Total Collection | Known Significance
| Stegomyia albopicta | 54.82% | Primary vector for dengue, chikungunya, Zika
| Culex quinquefasciatus | 6.92% | Vector for lymphatic filariasis
| Hulecoeteomyia chrysolineata | 6.33% | Noted for diverse breeding patterns
| Armigeres subalbatus | 5.03% | Nuisance mosquito, prefers polluted water
Identified Disease Vectors
The study identified 14 known disease vector species, creating a multifaceted public health risk. The co-existence of primary and secondary vectors for various diseases complicates transmission dynamics.
- Arboviruses (Dengue, Chikungunya, Zika, Japanese Encephalitis): St. albopicta, St. aegypti, Fredwardsius vittatus, Cx. tritaeniorhynchus, Cx. bitaeniorhynchus, Cx. gelidus, Cx. vishnui, Cx. pseudovishnui.
- Malaria: Anopheles stephensi, An. culicifacies (primary vectors), and An. varuna (secondary vector).
- Filariasis: Cx. quinquefasciatus, Mansonia uniformis, An. barbirostris.
While St. albopicta was abundant, other primary vectors were found in extremely low numbers, such as St. aegypti(1.43%), An. stephensi (0.06%), and An. culicifacies (0.01%). However, the study emphasizes that even low-density vector populations can sustain pathogen transmission cycles and cause outbreaks under favorable conditions.
3. Spatiotemporal Distribution and Biodiversity Hotspots
The distribution of mosquito species varied significantly across the five surveyed districts, revealing distinct biodiversity patterns influenced by local ecology.
District-Level Diversity
- Wayanad District: Identified as a definitive hotspot for mosquito diversity, with the highest species richness (64 species, including 14 unique to the district). This is attributed to its diverse ecological niches, extensive forest cover, coffee plantations, and comparatively low human interference.
- Thiruvananthapuram and Pathanamthitta Districts: Also exhibited high levels of diversity, with 60 and 59 species identified, respectively.
- Ernakulam District: Showed a moderate level of diversity with 54 recorded species.
- Idukki District: Displayed significantly lower species richness (34 species), a finding linked to the predominance of tea plantations, which do not provide suitable water-accumulating habitats for mosquito breeding.
A core group of 19 species was found across all five districts, indicating shared environmental determinants that support widespread mosquito populations.
Prevalence Patterns
Stegomyia albopicta was the predominant species in all five districts. In the Thiruvananthapuram district, it accounted for an exceptionally high 77.29% of collected mosquitoes. The second-most dominant species varied by district, suggesting that "one-size-fits-all" vector control methods would be ineffective and require tailored, localized strategies.
Species-Area Relationship
The study identified a statistically significant inverse relationship between mosquito species richness and the size of the geographic area sampled (S = 80.46–3.92 log AREA). This finding highlights the importance of spatial scaling in understanding and predicting mosquito biodiversity patterns.
4. Breeding Habitat Analysis and Vector Adaptability
A critical finding of the study is the role of human activity in creating ideal breeding environments for mosquitoes, particularly disease vectors.
Dominance of Artificial Habitats
Artificial, anthropogenic habitats were found to support a significantly greater diversity of mosquito species (77.7%) compared to natural habitats like tree holes and leaf axils (22.3%). This points to major deficiencies in solid waste management, as discarded items are primary breeding sites.
Adaptability of Stegomyia albopicta
This species demonstrated remarkable ecological flexibility and adaptability, posing a major challenge for control efforts.
- Habitat Range: St. albopicta was found breeding in 77 different types of habitats, both natural and artificial.
- Urban Adaptation: The species, historically considered a rural vector breeding in natural sites, has now thoroughly adapted to urban and peri-domestic environments, utilizing artificial containers.
- Key Breeding Sites:
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- Latex collection cups (10.57%)
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- Latex Collection Cups: A change in rubber plantation practices—switching from coconut shells to plastic cups held by metal wires—has inadvertently created permanent, rainwater-collecting breeding grounds for Aedesmosquitoes in the shady, favorable environment of plantations.
5. Significant Scientific Discoveries and Future Research Directions
The comprehensive survey led to several important taxonomic discoveries, expanding the known mosquito fauna of the region and highlighting areas for future investigation.
- New Species Described: A mosquito specimen initially identified as Heizmannia metallica was confirmed through detailed taxonomic analysis to be a new species, subsequently named Heizmannia rajagopalani.
- First Complete Description: The study provided the first-ever description of the adult male, larva, and pupa of the species Topomyia aureoventer, of which only the female had been previously documented in 1910.
- New Regional Records: The survey marked the first time that St. krombeini and species from the albopictussubgroup (St. subalbopicta, St. novalbopicta, St. pseudalbopicta) were reported in these districts of Kerala.
- Rare Genera with Unknown Potential: Rare species from the genera Heizmannia and Verrallina were observed exhibiting anthropophilic behavior (landing on humans). Their role in disease transmission in India remains unknown, representing a critical knowledge gap that requires further research into their vector competence.
6. Public Health Implications and Conclusion
This study provides an essential baseline for understanding mosquito ecology in Kerala and has profound implications for public health policy and disease control.
- Elevated Arbovirus Risk: The combination of St. albopicta's dominance, Kerala's history with a mutated chikungunya virus (A226V) adapted for this vector, and a high seroprevalence of dengue (30.9%) among children signals a severe and persistent risk of arboviral disease outbreaks.
- Need for Integrated Vector Management: The presence of 14 different vectors for arboviruses, malaria, and filariasis demands a comprehensive and integrated approach to surveillance and control that accounts for the unique biology and behavior of each species.
- Critical Role of Waste Management: The finding that artificial habitats are the primary drivers of vector diversity directly links inadequate solid waste management to public health risk. Controlling vector populations will require significant improvements in this area.
- Conclusion: The research provides invaluable insights into the diversity and distribution of mosquito species in Kerala. The findings underscore the urgent need for robust, continuous surveillance, targeted vector control strategies tailored to local ecological conditions, and further research to understand the vectorial capacity of newly identified and rare species. The remarkable adaptability of key vectors like St. albopicta poses a significant, ongoing challenge that requires innovative and sustained control efforts to protect public health.