Zoonotic malaria is an emerging public health issue, particularly in the Western part of Indonesia, including Kalimantan, where extensive forested regions create ideal environments for Anopheles mosquitoes (Indonesia, 2022). Although zoonotic malaria, primarily caused by Plasmodium knowlesi, has been widely reported in Malaysian Borneo, there are fewer recorded cases in Kalimantan (Indonesia part of Borneo) (Sugiarto et al., 2022). This difference prompts inquiries into vector distribution, human exposure, and the effectiveness of surveillance (Thevasagayam & Choon Fah, 1979); (Organization, 2025). In comparison to Malaysia, where zoonotic malaria accounts for 87.4% of malaria cases, Indonesia reports only 4.4% of malaria infections caused by P. knowlesi, the predominant agent of zoonotic malaria in Southeast Asia (Organization, 2025). Variations in mosquito ecology and biodiversity might explain this difference. At least five mosquito species are confirmed vectors of zoonotic malaria, and four more are suspected to play a role in its transmission.

In contrast, only two species have been recorded in Indonesia. Historical and contemporary entomological research has noted several Anopheles species in Kalimantan. Early investigations highlighted Anopheles roperi Reid, Anopheles letifer Sandosham, and Anopheles barbirostris van der Wulp as key vectors (Sugiarto et al., 2022). Anopheles letifer, Anopheles baezai Gater, and An. roperi, which belong to the Anopheles umbrosus (Theobald) group, have demonstrated varying levels of competence as malaria vectors for both humans and mouse deer (Wharton et al., 1963).

A comprehensive survey of malaria vectors in South Kalimantan identified Anopheles leucosphyrus Dönitz and Anopheles balabacensis Baisas as the dominant species, with sporozoite rates of 1.0% and 1.3%, respectively (I et al., 2022); (Harbach et al., 1987). Research conducted on Sebatik Island in North Kalimantan identified Anopheles vagus Dönitz, Anopheles sundaicus, (Rodenwaldt) and Anopheles subpictus Grassi as the most prevalent species, with both Anopheles peditaeniatus (Leicester) and An. sundaicus testing positive for Plasmodium falciparum(Sugiarto et al., 2017). Additionally, molecular investigations in Kotabaru, South Kalimantan, confirmed the presence of Plasmodium vivax in An. vagus, An. peditaeniatus, and Anopheles tessellatus Theobald, thus broadening the list of malaria vectors in the area (Sugiarto et al., 2022). Deforestation, agricultural land conversion, and urban sprawl have notably changed mosquito habitats in Kalimantan. Research conducted in Sarawak revealed that alterations in land use impact the abundance and behaviour of Anopheles species, thereby affecting malaria transmission dynamics (Chang et al., 1997). Similar trends are anticipated in Kalimantan, where extensive oil palm plantations and logging activities develop new breeding sites (Reid & Weitz, 1961).

Even with capable vectors, the low incidence of P. knowlesi reported in Kalimantan indicates potential underdiagnosis or variations in human-vector contact patterns. Recent molecular studies have identified P. knowlesi infections in a limited number of human cases in Central and South Kalimantan; however, standard diagnostic methods often struggle to distinguish P. knowlesi from other Plasmodium species (Ompusunggu et al., 2015).

This research aims to explore the diversity of mosquitoes, particularly Anopheles species, in regions with a high risk of zoonotic malaria transmission in Central Kalimantan. This study intends to identify vector mosquitoes and their bionomic traits, laying a vital groundwork for effective malaria control strategies. This study strongly believes that precise identification is a critical initial step in effectively managing vectorborne diseases.

Biodiversity exerts a considerable influence on human health, particularly in the context of diseases that depend on both reservoir hosts and vectors for transmission. Alterations in biodiversity can influence the risk of disease spread, with this influence being either positive or negative, depending on the nature of the ecological change in question. Ostfeld & Keesing’s “dilution effect” hypothesis posits that greater biodiversity may lead to a reduction in disease transmission by spreading pathogens among a diverse array of host species with differing competency levels. Consequently, the probability of a pathogen being transmitted back to humans or vectors is reduced due to the presence of less competent or non-amplifying hosts (Ostfeld & Keesing, 2011); (Ostfeld, 2009). This study provides significant insights into the diversity and ecology of mosquito species, particularly Anopheles, across diverse ecological sites in Central Kalimantan, which may facilitate zoonotic malaria transmission. The ecological and geographical characteristics of the surveyed areas are indicative of a range of landscape characteristics and patterns of human settlement that could potentially impact the composition and distribution of mosquito species. Despite all study locations being at similar elevations (0 m above sea level), they varied significantly in terms of habitat types, vegetation cover, human settlement density, land use, and distance to water sources. These elements are crucial in mosquito ecology and the dynamics of vector-borne diseases (Ferraguti et al., 2020); (Ndoen et al., 2010). In general, the abundance and diversity of mosquitoes are lower in human-altered environments than in natural habitats. However, it is worth noting that species-specific reactions to habitat changes may vary. While many species of mosquito experience a decline in abundance due to higher levels of urbanization, deforestation, and agricultural expansion, species of significant global health concern often show increased numbers in human-modified environments (Perrin et al., 2022). The Nyaru Menteng and Bukit Tangkiling areas are located within secondary forest regions, distinguished by their dense vegetation and moderate to low levels of human settlement. These regions are linked to natural or semi-natural water sources, such as swamps and artificial ponds, which provide favourable breeding grounds for forest-dwelling Anopheles species. The combination of land uses, particularly the juxtaposition of forest and farmland in Nyaru Menteng, suggests a potential intersection between vector habitats and human activities. This raises concerns about the possibility of zoonotic transmission. This is evidenced by the markedly elevated counts of mosquito species and genera recorded in this area, in comparison to other areas that have been surveyed.

The Jalan Pariwisata and the airport employee residential area represent more anthropogenically modified environments, characterized by sparse vegetation, plantation or urban residential land use, and proximity to artificial water sources such as roadside and irrigation ditches. The sparse vegetation and high human activity levels present in these locations may provide a conducive environment for the proliferation of opportunistic mosquito species that are well adapted to urban or peri-urban settings, including several Culex and Aedes species. The presence of extensive swamp areas in the residential area surrounding the airport has led to the dominance of Mansonia mosquitoes, typically associated with swamps, in the results of mosquito collections (Apiwathnasorn et al., 2006); (Becker et al., 2020).

Anopheles letifer has emerged as the predominant Anopheles species, representing 97% of all Anopheles collected, with the greatest density observed in Nyaru Menteng. This finding corroborates earlier research indicating that An. letifer is predominantly found in forested, swamp-forest, and semi-urban areas of Southeast Asia, flourishing in regions with ample breeding habitats and accessible human hosts (Wharton et al., 1963). In Sarawak, Malaysia, the species under discussion typically breeds in dark brown, peaty swamp waters and is often encountered in large quantities in jungle clearings and at the edges of forests. This species is seldom encountered deep within the jungle, where its sibling species, An. umbrosus, is more prevalent (Thevasagayam & Choon Fah, 1979). Its proximity to the forest edge heightens the chances of An. letifer interacting with local residents, which positions it as a potential malaria vector. This assertion is supportted by documented cases of sporozoite rates reaching 0.23% in Sarawak, Malaysia, and 1.01% in Palangkaraya, Indonesia (Chang et al., 1997); (Permana et al., 2023). It is evident that several members of the Umbrosus group, including An. letifer, An. collesi, and An. roperi, function as primary vectors for zoonotic malaria (Ali et al., 2023). The presence of An. letifer in Central Kalimantan, particularly in regions inhabited by primates such as orangutans, macaques, and Hylobates, has led to concerns regarding the potential for zoonotic malaria transmission. Across all five study locations, long-tailed macaques (Macaca fascicularis) were frequently observed in proximity to residential areas, suggesting a likely association with nearby forest habitats. Nevertheless, An. letifer was predominantly found only in Nyaru Menteng among the five sites. Three species of Anopheles are known to contribute to zoonotic malaria in Kalimantan. The following species are hereby identified: An. leucosphyrus Dönitz, An. balabacensis, and An. latens Sallum & Peyton.

In this study, An. letifer primarily exhibited outdoor biting behaviour, with activity commencing in the early evening, reaching its apex shortly after dusk, and resuming during the latter part of the night. The trendline demonstrates a marked tendency for elevated average biting rates in outdoor environments, indicating a discernible predilection for nocturnal outdoor biting. This finding is of crucial importance for malaria vector control, particularly in areas where individuals are active outdoors or sleep in unscreened homes at night (Rozi et al., 2024); (Rozi et al., 2025). Research conducted in Selangor, Malaysia, revealed that more than 95% of An. letifer feeds at night, with peak biting activity occurring between 22:00 and 24:00. A smaller fraction of An. letifer collected from Selangor was found during the morning or daytime, primarily in forested regions or in close proximity to human residences (Sugiarto et al., 2022). In this study, mosquito collection was restricted to the hours between 18:00 and 06:00. The presence of mosquitoes during crepuscular periods, such as dusk and dawn, suggests the possibility of enhanced activity extending beyond these times, particularly in the early morning and late afternoon. This atypical daytime biting behaviour may result from low light conditions found in forest habitats, which can resemble twilight and possibly stimulate nocturnal activity patterns even during the day. The HBR is a measurement of the number of bites that a person encounters from a specific species of mosquito. A study of data collected from six different locations revealed that the Mansonia species exhibited the highest rate of biting, with an average of 18.03 bites per person per night (Organization, 2013). This finding indicates a high level of human exposure to Mansonia mosquitoes, suggesting their potential role as a significant nuisance and a possible vector for filariasis in the area (Becker et al., 2020); (Alonso et al., 2023). An. letifer exhibited the second highest HBR of 5.48, indicating a considerable malaria transmission risk, particularly in regions with high populations of An. letifer, such as Nyaru Menteng. In contrast, other Anopheles species, including An. umbrosus and An. tessellatus, exhibited remarkably low HBR values (0.13 and 0.03, respectively), suggesting minimal human-vector interaction. The disparities in HBR among different species and geographical locations emphasise the importance of localised vector monitoring to inform targeted control initiatives.

The entomological findings were corroborated by breeding site surveys, which revealed the presence of Anopheles larvae in 13 out of 48 sites (27%). Despite the absence of statistically significant relationships between specific environmental factors and the presence of Anopheles larvae (p > 0.05), certain habitat types demonstrated consistent patterns. For instance, swamps and stream edges were identified as the most productive habitats, with each exhibiting a positivity rate of 67%. These environments frequently contain shaded, vegetated areas with stagnant water, which are conducive to Anopheles oviposition and larval growth (Adugna et al., 2025). The correlation between swamps and malaria cases has been documented since ancient Greece, a period preceding the understanding of mosquitoes as vectors. At that time, efforts were already underway to drain swamps and marshlands as a malaria risk mitigation strategy (Kousoulis et al., 2013); (Britannica, 2025).

Peat-swamp forests are influenced by a range of spatial and temporal factors, primarily due to the nutrient-poor, highly acidic, and waterlogged nature of their peat soils (Mirmanto, 2010); (Nishimua et al., 2007). In Central Kalimantan, the terrain comprises a mosaic of peat-swamp forest mixed with tropical heath forest, spanning roughly 4.3 million hectares of wetland, 0.7 million hectares of tidal swamps and 3.6 million hectares of non-tidal swamps (Nishimua et al., 2007); (Mulyono, 2023); (Sukarna & Birawa, 2018); (Noor et al., 2023). The swamps and the dark brown, peaty water typically found in jungle clearings and at forest margins provide a natural habitat for An. letifer and An. umbrosus, which are often found in large populations (Thevasagayam & Choon Fah, 1979). It is estimated that over 27% of Central Kalimantan is vulnerable to malaria transmission due to the presence of these mosquito species in the peat-swamp areas. Furthermore, human activities in forested areas and settlements within these zones serve to exacerbate the risk.

Seepages and ponds were found to harbour relatively high numbers of Anopheles larvae. This finding suggests that semi-permanent water bodies, characterised by moderate sunlight exposure and abundant vegetation, can function as vital larval habitats. It is noteworthy that artificial water-filled structures such as ditches and discarded containers (including water-filled wrecks) exhibited a less consistent correlation with larval presence, despite their recognised capacity to support mosquito growth in other contexts. The variation in larval presence among different habitat types emphasises the necessity of performing sitespecific habitat evaluations instead of relying solely on broad classifications. Nevertheless, trends indicate that specific types of breeding sites, water conditions, and vegetation presence might impact mosquito distribution. Further research employing larger sample sizes could yield more comprehensive insights into the ecological determinants of Anopheles breeding in the study area.

The absence of statistically significant associations in this research could be attributed to the limited sample size and narrow temporal range. Previous research indicates that the presence of Anopheles larvae is affected by water quality and various physical, chemical, and biological traits of breeding sites (A et al., 2021). Sunlight exposure notably impacts larval density, with a strong positive correlation between sunlight and larval abundance (Tsegaye et al., 2023). Additionally, water depth, transparency, and aquatic vegetation are key habitat characteristics that influence the occurrence and abundance of Anopheles larvae (Teklu et al., 2010). However, this study’s limitations— such as a small number of larval habitats, single crosssectional surveys, and broad environmental categories without detailed physicochemical data—may have hindered the identification of relationships with environmental factors.

It is imperative to comprehend the biting behavior of malaria vectors, encompassing the optimal times and preferred locations for biting, as well as their larval habitats, to formulate effective disease control strategies (Esayas et al., 2024); (Elyazar et al., 2013); (Manguin et al., 2008); (Subbarao et al., 2019). The exophagic tendency indicates that traditional indoor control is less effective.

These two primary malaria prevention methods— bed nets and IRS—offer protection mainly when people are resting or sleeping indoors. As a result, outdoor mosquito bites that cause transmission continue to be a concern. Several potential methods could address outdoor transmission, including insecticide-treated hammocks and clothing, spatial and topical repellents, and barrier screens, all designed to minimize human– mosquito interactions. This study emphasizes the importance of implementing Integrated Vector Management (IVM) strategies customized to Central Kalimantan’s ecological and social conditions. Since An. letifer breeds mainly close to human settlements and exhibits exophagic biting behavior, traditional methods like IRS and LLINs are less effective. Consequently, localized IVM strategies are essential, such as larval source control in semi-permanent swamp areas, community-led environmental modifications and water management, and outdoor protection measures. (Burton et al., 2025); (Rozi et al., 2025). Primary health centers can significantly contribute to health promotion by raising awareness and encouraging behavioral changes to reduce outdoor mosquito exposure at night (Duana et al., 2021); (Groepe et al., 2013); (Onyinyechi et al., 2023). This includes educational campaigns that promote protective clothing, repellents, and insecticide-treated hammocks for those who are active outdoors after sunset.

Additionally, conducting targeted vector surveillance in forest-edge settlements, where humans and non-human primates interact, is crucial for mitigating the risk of zoonotic malaria transmission (Permana et al., 2023). These approaches, executed within a One Health framework, are well-adapted to the ecological context of peat swamp areas and respect local socio-cultural practices. This study provides important insights into the diversity and biting behavior of Anopheles mosquitoes in Central Kalimantan, but some aspects should be interpreted with caution.

The entomological collections were limited to two cross-sectional periods, which did not allow for a full assessment of seasonal variation. The number of larval habitats surveyed was also relatively small, and environmental variables were described broadly rather than through detailed physicochemical measurements. Additionally, the five study sites may not cover all ecological settings across Central Kalimantan. These points suggest that future longitudinal surveys covering multiple seasons, a larger number of larval habitats, and a broader ecological range will be useful to build on and extend the current findings.

This study emphasises the substantial biodiversity and ecological adaptations exhibited by mosquito species, notably An. letifer, in Palangkaraya, Central Kalimantan, underscoring the potential for zoonotic malaria transmission. The predominance of An. letifer in seminatural areas such as Nyaru Menteng, in conjunction with its outdoor biting behaviour and propensity for swampy, peaty habitats, underscores its potential role as a malaria vector in communities situated in proximity to forest edges. The close proximity of human settlements to forested areas inhabited by nonhuman primates further elevates the risk of spillover transmission. These findings underscore the necessity of integrating ecological and entomological data when assessing the risk of vector-borne diseases in biodiverse and changing landscapes.