Nature's Solution to Aedes Vectors: Toxorhynchites as a Biocontrol Agent

Abstract

This review summarizes the predatory potential of Toxorhynchites mosquitoes as biological control agents for Aedes vectors. A single larva can consume hundreds of mosquito larvae during its development, with preference for larger prey and higher consumption rates at higher prey densities. Studies suggest Toxorhynchites can significantly reduce Aedes populations. Beyond direct predation, they may indirectly influence prey behavior and adult mosquito lifespan. Despite the demonstrably positive effects of Toxorhynchites species as biocontrol agents, there are acknowledged limitations that require further investigation. These limitations include potential variations in effectiveness across diverse habitats and mosquito developmental stages. Additionally, long-term ecological sustainability and potential ramifications warrant further research. Future efforts should prioritize optimizing rearing and release strategies to enhance effectiveness. Exploring the potential for combined control methods with other biocontrol agents or traditional methods is also crucial. Finally, investigating the influence of environmental factors on predation rates can further refine and optimize the application of Toxorhynchites in mosquito control programs.

1. Introduction

Mosquitoes are notorious vectors for a multitude of diseases worldwide, as the genera Aedes, Anopheles, and Culex are important vectors of mosquito-borne diseases [1]. Among them, Aedes spp. are vectors for many arboviruses. The two major species, Aedes aegypti (Linnaeus 1762) and Aedes albopictus (Skuse 1894), are related to emerging or reemerging infectious diseases resulting serious public health concerns [2]. Aedes mosquitoes are diurnal, target both animals and humans for blood meals, and have earned notoriety for their capacity to transmit over 20 viruses and filarial worms, including those with severe implications to human health [3]. Two species Aedes aegypti and Aedes albopictus were originated from the African continent and Southeast Asian forests, respectively. They are proficient vectors of chikungunya virus, dengue virus, yellow fever virus, and zika virus, inflicting significant health repercussions and economic losses worldwide.

Dengue fever, the most prevalent mosquito-borne disease, has seen a tenfold increase in reported cases globally between 2000 and 2019 [4]. This translates to more than 3.9 billion people in over 129 countries being affected, with over 40,000 deaths every year [5]. While Asia carries about 70% of world's disease burden, the Americas, Southeast Asia, and the Western Pacific are hardest hit. The situation worsens as dengue fever creeps into new areas like Europe, while existing regions experience intense regular outbreaks [6]. According to the WHO, the Americas experienced the most cases in 2023 with over 4 million reported, highlighting this growing threat. Southeast Asia remains a major hotspot with countries like Thailand and Vietnam experiencing high numbers of casualties [4]. Africa also faces a rising burden with outbreaks in 15 countries. Similarly, the Eastern Mediterranean region is experiencing an increase, with nine countries regularly facing outbreaks. While Europe is not considered endemic, a few countries like Italy, France, and Spain did report outbreaks in 2023 [4]. Thus, this rise in mosquito-borne diseases is of global concern. Chikungunya, another Aedes-borne disease, saw major outbreaks in East Africa, the Indian Ocean (2005-2006), and the Americas and Oceania (2013-2014) [7–9]. Zika also caused major outbreaks in the Americas (2015-2016) [9]. Moreover, yellow fever has reemerged with recent epidemics in sub-Saharan Africa and Brazil [10].

The primary strategy to minimize the risk of mosquito-borne infections involves reducing mosquito populations [11]. The emergence of insecticide resistance and the detrimental effects of conventional insecticides on the environment have fueled a growing interest in biological control methods for mosquito vector management [12]. Various biocontrol agents from the insect orders Diptera, Odonata, Coleoptera, and Hemiptera have been explored globally to control mosquito populations [13]. From the outset, scientists have recognized the value of utilizing the natural predator-prey relationships within the environment for effective mosquito control. These natural predators including juvenile fish, Odonata larvae (dragonfly and damselfly nymphs), and mosquito larvae offer a sustainable and environmentally friendly approach to control mosquito [14–16]. A fascinating paradox exists among these predators: the Toxorhynchites mosquito. These giants of the mosquito world, nicknamed “elephant mosquitoes” or “mosquito eaters,” possess a proboscis specifically adapted for nectar, not blood. Toxorhynchites mosquitoes, primarily tropical dwellers found in the lush forests of equatorial and tropical regions, have a distribution that generally falls within a band between 35° north and 35° south latitude [17]. However, there are a few exceptions. Some species, like Toxorhynchites rutilus, has adapted to the temperate zones of the Northern Hemisphere [18] with a wider range within North America, stretching from Mexico all the way to the Atlantic coast [19, 20]. While a few species have ventured beyond the tropics, Southeast Asia remains a hotspot for Toxorhynchites diversity, boasting as many as 24 documented species [21].

The larvae of Toxorhynchites mosquitoes hold immense potential for mosquito control [22, 23]. These larvae are exceptional predators throughout their development, particularly adept at preying on mosquito larvae of public health significance, such as Aedes aegypti (L.), Aedes albopictus (Skuse), and Culex quinquefasciatus [24, 25]. Interestingly, Toxorhynchites often lay eggs in the same containers favored by Aedes aegypti and Aedes albopictus [26, 27]. A single Toxorhynchites larva can devour a staggering number of prey larvae—up to several thousand during their whole larva stage [22]. Their predatory prowess extends beyond direct consumption. Toxorhynchites larvae exhibit a fascinating behavior known as compulsive killing, where they kill mosquito larvae but leave them uneaten, especially before pupation [28]. Additionally, they can indirectly influence prey development, further hindering their population growth [29]. Consequently, Toxorhynchites larvae represent a promising model for Aedes mosquito control. Therefore, the aim of the current review is to analyze the role of Toxorhynchites larvae in the control of Aedes mosquito around the world.

2. Methods

We conducted a comprehensive search for articles in Science Citation Index (SCI)-indexed journals, focusing on Aedes mosquito control and the potential of Toxorhynchites as a biocontrol agent. Utilizing PubMed and Research4Life, we searched using the keywords “Aedes control” and “Toxorhynchites” to capture relevant strategies and the specific role of Toxorhynchites. The initial search yielded 269 articles. To maintain high scientific rigor and align with the review's objectives, we applied specific inclusion/exclusion criteria related to Aedes control and Toxorhynchites' biocontrol role. This resulted in a final selection of 42 articles for detailed analysis (Figure 1). To deeply understand existing research, a standardized data extraction method was employed, collecting information on study design, methodology, key findings, and limitations from each article (Supplementary Table 1).

Figure 1.

Research design.

2.1. Inclusion Criteria

1. Studies investigated the use of Toxorhynchites larvae or adults for controlling Aedes mosquito populations.

2. Studies evaluated the effectiveness of Toxorhynchites in reducing Aedes mosquito breeding or biting rates.

3. Studies conducted in laboratory or field settings that explored the predatory behavior of Toxorhynchites toward Aedes mosquito larvae.

4. Studies published in English in the last 51 years (1972 to 2023).

2.2. Exclusion Criteria

1. Studies focused on Toxorhynchites for purposes other than Aedes mosquito control (e.g., their biology, taxonomy, and distribution).

2. Studies only mentioned Toxorhynchites in passing without any data on their use in biocontrol.

3. Studies published in journals that are not SCI-indexed.

4. Studies published in languages other than English (unless translations were available).

3. Results

3.1. Global Distribution

Toxorhynchites mosquitoes boast an impressive global presence, extending across continents from Asia (Indonesia, India, and Thailand) to Africa (Tanzania) and North America (Florida, USA, and Mexico). Toxorhynchites splendens notably demonstrated a wide distribution, encompassing Bangladesh, Nepal, Myanmar, and Sri Lanka (Table 1). Building on this diversity, Table 2 highlights 13 potential Toxorhynchites species that could be recruited to the fight against mosquitoes, demonstrating the genus's promising role in biocontrol solutions.

Table 1.

Geographical distribution of Toxorhynchites.

S.N.	Species	Country	Source
1	Tx. acaudatus	Indonesia	[21]
2	Tx. albipes	India and Thailand
3	Tx. amboinensis	Indonesia	[21, 30–34]
4	Tx. auranticauda	Indonesia	[21]
5	Tx. aurifluus	Taiwan
6	Tx. bengalensis	Bangladesh
7	Tx. bickleyi	Thailand
8	Tx. brevipalpis	Tanzania (Africa), United Kingdom, USA	[21, 27, 34, 35]
9	Tx. coeruleus	Indonesia	[21]
10	Tx. christophi	DPR Korea
11	Tx. edwardsi	India
12	Tx. gravelyi	India and Thailand
13	Tx. guadeloupensis	Brazil
14	Tx. inornatus	Indonesia
15	Tx. kempi	India, Indonesia
16	Tx. klossi	India
17	Tx. leicesteri	Thailand
18	Tx. magnificus	Thailand
19	Tx. manicatus	Taiwan
20	Tx. manopi	Thailand
21	Tx. metallicus	India and Indonesia
22	Tx. minimus	India, Indonesia, and Sri Lanka
23	Tx. moctezuma	Mexico, USA	[21, 36–39]
24	Tx. quasiferox	Indonesia	[21]
25	Tx. rutilus	Florida (USA)	[21, 34, 40–42]
26	Tx. speciosus	Indonesia	[21]
27	Tx. splendens	Bangladesh, India, Indonesia, Nepal, Myanmar, Sri Lanka, Malaysia, Philippines, Japan, USA, and Thailand	[21, 26, 34, 43–51]
28	Tx. sumatranus	Indonesia	[21]
29	Tx. sunthorni	Thailand
30	Tx. towadensis	Florida, Japan	[21, 52]
31	Tx. tyagii	India	[21]
32	Toxorhynchites violaceus	Brazil	[53]
33	Toxorhynchites theobaldi	Brazil, USA	[34, 54]

Table 2.

Global utilization of Toxorhynchites species for biological control.

S. N	Species	Country	Citation
1	Toxorhynchites rutilus	Florida (USA)	[20, 55]
2	Toxorhynchites splendens	Malaysia, Indonesia, Russia, India, and USA	[26, 29, 44, 47, 48, 50, 56, 57]
3	Toxorhynchites amboinensis	Florida, Texas, Louisiana (America), Mexico, Philippines, and Malaysia	[24, 30–32, 42, 48, 58, 59]
4	Toxorhynchites towadensis	Florida	[22, 28]
5	Toxorhynchites moctezuma	Mexico, USA	[36, 39]
6	Toxorhynchites brevipalpis	Tanzania (Africa)	[27, 60]
7	Toxorhynchites	Brazil	[61]
8	Toxorhynchites christophi	Korea	[62]
9	Toxorhynchites aurifluus	Taiwan	[63]
10	Toxorhynchites manicatus	Taiwan	[63]
11	Toxorhynchites theobaldi	Brazil	[54]
12	Toxorhynchites violaceus	Brazil	[53]
13	Toxorhynchites minimus	Sri Lanka	[46]

3.2. Toxorhynchites Record from Nepal

Only one species of Toxorhynchites (Tx. splendens) has been documented in Nepal. Toxorhynchites splendens was first recorded in 1956 by Peter and Dewar [64]. It has been documented in Sunsari, Rupandehi, Jogikuti, Sindhuli, and Khuntpani in Nepal, as reported by Darsie and Pradhan in 1990 [65]. It has also been reported from the Banke district by Darsie et al. in 1996 [43]. However, there have been no published records of Toxorhynchites in Nepal after 1996.

3.3. Promising Species for Biocontrol

Several Toxorhynchites species show high potential as biological control agents for mosquito populations, particularly Aedes aegypti, and the vector of dengue hemorrhagic fever. Their key strengths lie in their predatory efficiency and eco-friendly nature. Many Toxorhynchites larvae are voracious predators, consuming hundreds of mosquito larvae per individual throughout their lifespan [44, 45]. Field trials documented reductions in Aedes populations by up to 83% after Toxorhynchites introductions [46]. Unlike chemical insecticides, Toxorhynchites pose minimal risk to nontarget organisms and the environment [36, 47]. This makes them particularly attractive for areas with environmental, biodiversity, and other concerns.

3.3.1. Toxorhynchites splendens

Toxorhynchites splendens larvae are known to be efficient predators, consuming a significant number of prey larvae daily. Studies show impressive predation rates in the laboratory. For example, single third-instar larvae in West Bengal, India, have been observed to consume over 50 Ae. albopictus larvae daily [44]. Similar results were observed in Okinawa, Japan, where research recorded that fourth-instar Tx. splendens larvae could consume as many as 55 Ae. albopictus larvae daily, while third-instar larvae exhibited a lower predation rate, consuming around 20 larvae per day [45]. Another study in Sri Lanka demonstrated that third- and fourth-stage larvae of Tx. splendens could devour one Ae. albopictus larvae in about 30 minutes [46]. Even with some studies showing lower predation rates [48], the effectiveness of Tx. splendens translates encouragingly from laboratory to real-world settings. Semifield experiments showed significant reductions in Ae. albopictus larvae [44]. Field trials documented up to 83% decline in Aedes populations following Tx. splendens introductions [46]. Additionally, a negative correlation between Tx. splendens and Ae. albopictus larvae in ovitraps was observed [26]. Even monthly adult releases effectively reduced target mosquito broods in containers [49]. However, factors such as container type and prey density (offering 10 to 50 prey individuals per predator) influenced Tx. splendens predation rates, with horizontal containers with wide openings being more suitable [48].

Additionally, experiments explored Tx. splendens' feeding activity in the presence of alternative food, reaffirming its role as a mosquito larvae predator. They exhibit a clear preference for consuming mosquito larvae, and their consumption is inversely proportional to the search area and directly proportional to prey density (the number of prey given) [44, 50]. Interestingly, fourth-instar Tx. splendens larvae might also kill prey without consuming them [45]. Researchers also investigated Tx. splendens' behavior to optimize control programs, revealing hunting preferences for Aedes aegypti over Aedes albopictus, with predation increasing with prey density [51]. Tx. splendens larvae prefer Aedes larvae of the respective stages [45, 51], with a preference for Ae. aegypti larvae over Ae. albopictus and Anopheles sinensis due to more active movements [47]. However, Tx. splendens larvae exhibited a slightly lower predation ability for Ae. aegypti compared to Culex quinquefasciatus (10.6 vs. 12 larvae/day) [50].

Research suggests Tx. splendens larvae may even kill prey without consuming them. While this highlights their effectiveness, the long-term ecological implications need thorough investigation. Furthermore, complete eradication of target mosquito populations might not be achievable solely with Tx. splendens releases [46]. Integrated control programs combining Tx. splendens with other methods may be necessary. However, potential ecological impacts and limitations on complete eradication necessitate a cautious approach with Tx. splendens as a biocontrol agent.

3.3.2. Toxorhynchites amboinensis

Laboratory studies reported that a single predator larva can consume more than 230 prey larvae on average throughout its larval stage at lower prey density (20 Ae. aegypti larvae/200 ml water/Toxorhynchites larva). Interestingly, it moves more than 350 times at higher prey density (Ae. aegypti larvae/200 ml water/Toxorhynchites larva) [50] regardless of the prey species offered (Ae. aegypti, Ae. albopictus, and Cx. quinquefasciatus). These findings highlight Tx. amboinensis as a potential predator for a variety of mosquito larvae, such as Aedes aegypti, Aedes albopictus, and Culex quinquefasciatus. The fourth-instar larvae were found to be the most predacious, with compulsive predation observed during the late stage of this instar [30], confirming its predatory efficacy and pinpointing the fourth-instar larvae as the most effective stage. Interestingly, these studies also revealed a preference for mosquito larvae by Tx. amboinensis, with higher predation rates at higher prey densities. It suggests Tx. amboinensis can be a valuable component of an integrated mosquito control strategy, potentially offering both environmental and health benefits by reducing reliance on chemical insecticides due to its preference for mosquito larvae and increased predation at higher prey densities.

Field trials investigated Tx. amboinensis as a promising biological agent for mosquito control. Studies in New Orleans [31] demonstrated significant reductions (up to 45%) in Ae. aegypti densities following weekly releases of Tx. amboinensis larvae. This predator's effectiveness was further amplified when combined with reduced insecticide use. When integrated with Malathion, mosquito control reached up to 96% compared to 29% with Malathion alone [32]. Interestingly, increasing the number of Tx. amboinensis released did not yield additional control, suggesting researchers could develop optimized release strategies [31]. However, the success rate of Aedes spp. control by Tx. amboinensis depends greatly on the type of habitat, as the mean overall reduction of Aedes by the introduction of Tx. amboinensis was recorded as 22% in tins and 63% in tires over a 10-month period in Wailoku Village and Yanuca Island [33]. Habitat suitability assessments were therefore essential for determining the feasibility of Tx. amboinensis as a control agent in specific locations. Overall, Tx. amboinensis demonstrated promise as a biological control agent for vector mosquito species. Its effectiveness as a predator, potential for integration with reduced insecticide use, and environmentally friendly approach make it a valuable candidate for further development. However, successful implementation requires careful consideration of release strategies, habitat suitability, and ecosystem dynamics. Future research should focus on optimizing these aspects to maximize the potential of Tx. amboinensis for sustainable mosquito control.

3.3.3. Toxorhynchites moctezuma

A dose-dependent effect, with more Tx. moctezuma larvae leading to a sharper decline in Ae. aegypti emergence, was documented in the experiment conducted at the Caribbean Epidemiology Centre in Spain. One or two Tx. moctezuma larvae could halt adult Ae. aegypti emergence for a week, and five or ten larvae could prevent emergence for up to 16 weeks [37]. Additionally, sustained releases of Tx. moctezuma larvae for five months resulted in lower mosquito indices in released villages relative to unreleased ones [38], suggesting long-term effectiveness. Tx. moctezuma larvae exhibit minimal cannibalism, but their fourth-instar stage displays compulsive killing behavior [37]. These contrasting traits present both challenges and opportunities for their use as biocontrol agents. The successful suppression of Ae. aegypti populations through systematic releases of Tx. moctezuma larvae on Union Island [39] further bolstered the case for this biological control method. However, a decline in Tx. moctezuma's effectiveness over time was observed [36], highlighting the need for research on maintaining long-term control. Most studies focused on single-release events or short-term trials [37, 39]. Therefore, large-scale field studies were needed to assess long-term efficacy and ecological impact. Additionally, cost-effective rearing and release strategies were not addressed in the presented studies. Overall, the evidence strongly supports the potential of Tx. moctezuma larvae as a powerful biological control agent for Ae. aegypti. However, further research is necessary to address limitations like diminishing control over time, develop practical rearing and release methods, and conduct a thorough assessment of potential ecological impacts before widespread implementation.

3.3.4. Toxorhynchites rutilus

Tx. rutilus larvae emerged as efficient predators in past studies [40, 66]. A single larva could consume or kill nearly 50 mosquito immatures daily, exceeding 300 during development [40]. Another research documented as many as 400 prey larvae during their larval development and also demonstrated killing prey without consuming it [40, 66], which could significantly reduce potential adult Ae. aegypti emergence. The fourth-instar Tx. rutilus were more likely to kill pupae than the larvae of the same age. Interestingly, they completely ignored the first instar altogether [40]. This preference for larger prey size suggests a potential limitation for Tx. rutilus as a biocontrol agent—while powerful; it might not be equally effective against all mosquito life stages. Additionally, studies documented cannibalism occurring in confined spaces with limited resources [66]. Understanding and mitigating these behaviors are crucial for optimizing the effectiveness and sustainability of Tx. rutilus-based interventions. However, natural populations of Tx. rutilus were often insufficient for mosquito control, necessitating the rearing and release of additional adults. This approach increases complexity and cost. Additionally, the effectiveness of Tx. rutilus releases relied on precise timing, requiring releases before mosquito populations surged [41]. Adult dependence on nectar sources added another layer of complexity [41]. Availability of suitable nectar sources can limit their effectiveness in certain areas. While such programs offer potential advantages like dispersal and positive public perception, successful implementation requires careful planning, monitoring, and adaptation to local conditions. A study investigating the combined effects of pyriproxyfen (an insecticide) and Tx. rutilus on Ae. aegypti found that the combined approach significantly inhibited adult emergence compared to using either method alone [42]. However, further research with larger sample sizes and diverse field conditions is necessary to confirm these findings and assess the long-term efficacy and ecological implications of this combined approach. Overall, Tx. rutilus showed promise as a biological control agent, but its limitations necessitate a multifaceted approach. Future research can refine rearing and release strategies, alongside exploring complementary control methods, to maximize effectiveness of Tx. rutilus in managing Ae. aegypti populations.

3.3.5. Toxorhynchites brevipalpis

A detailed analysis conducted at the Department of Biology, University of Notre Dame, Indiana, revealed that predation rates of Tx. brevipalpis on Ae. aegypti larvae varied with temperature, with the highest predation (n = 358) observed at 30–32°C during larval development [27]. Interestingly, Tx. brevipalpis also killed prey larvae nearing pupation without consumption [27]. Similarly, combining Metarhizium brunneum fungus with Tx. brevipalpis larvae resulted in significantly lower Ae. aegypti larval survival rates than using either approach alone [35]. However, generalizing these laboratory findings to field applications requires careful consideration of ecological complexities and practicalities. Future research should prioritize field trials to validate the efficacy and sustainability of combined control strategies.

3.3.6. Toxorhynchites violaceus

Experiments performed in the laboratory to find the survival rate of fourth-instar larvae of Ae. aegypti in the presence of fourth-instar larvae of Tx. violaceus showed that although the initial survival rate was 98% in 24 hours, it decreased subsequently, reaching 0% by 192 hours [53]. This suggests a significant increase in the predatory potential of Tx. violaceus fourth-instar larvae for consuming Ae. aegypti larvae, ultimately leading to the elimination of all Ae. aegypti larvae. While this laboratory experiment was promising, the real-world effectiveness of Tx. violaceus remained uncertain. Furthermore, field testing is imperative as natural environments introduce complexities that laboratory settings cannot fully replicate.

3.3.7. Toxorhynchites towadensis

Tx. towadensis exhibited a curious behavior of killing prey without consuming them at high prey densities. While the study offers valuable insights, its generalizability is limited by the artificial setting. Real-world environments present greater complexities in prey availability, habitat structure, and potential interactions with other species. Future research should explore how these factors interact with prey density to provide a more holistic understanding of Tx. towadensis' predatory behavior in natural settings. Moreover, the study solely focused on prey density. Investigating the influence of prey type and environmental conditions on Tx. towadensis' behavior and development would provide a more comprehensive picture of its potential role in mosquito population control strategies [52].

3.3.8. Toxorhynchites theobaldi

Aedes aegypti mosquitoes, instead of avoiding predators, preferred oviposition sites with evidence of Tx. theobaldi predation (including dead conspecific larvae) due to the increased bacterial abundance by Tx. theobaldi feeding activity [54]. The study sheds light on the intricate web of indirect effects within predator-prey interactions, where predation can influence prey behavior through alterations in the microbial community. This suggests a potential double benefit for employing Tx. theobaldi as a biocontrol agent: direct reduction of prey populations and the inadvertent attraction of egg-laying mosquitoes to areas where their offspring are more susceptible to predation [54]. However, limitations exist. The laboratory setting might not fully capture the complexities influencing oviposition choices in natural environments. Additionally, the study focused solely on bacterial cues. Future research should explore the specific bacterial strains involved and how they interact with other environmental factors influencing mosquito behavior.

3.4. Combined Study of Different Species

An investigation of feeding strategies in five Toxorhynchites mosquito species (Tx. amboinensis, Tx. rutilus, Tx. theobaldi, Tx. brevipalpis, and Tx. splendens) found no significant difference in the average number of strikes needed for a successful capture across all species. However, Tx. amboinensis (37 prey/day) and Tx. brevipalpis (35 prey/day) captured prey at a significantly higher rate than Tx. splendens (27 prey/day), Tx. theobaldi (25 prey/day), and Tx. rutilus (19 prey/day) [34]. Interestingly, Tx. theobaldi exhibited a higher daily consumption rate (18.9 ± 0.97 prey/day) than other predators, even killing prey beyond their immediate needs before pupation [34]. These findings suggest potential variations in feeding strategies among Toxorhynchites species. Future research should delve deeper, investigating factors like predatory activity, handling time, and prey type to provide a more comprehensive understanding of these species' feeding strategies. Furthermore, examining if these patterns hold true across all developmental stages, from larvae to adult, is crucial for a complete picture.

3.5. Usefulness of Other Insects Other than Toxorhynchites

Some other invertebrates such as copepods, dragonflies, and damselflies are also predators of mosquito larvae. Copepods are highly effective predators, capable of significantly reducing larval populations, even achieving complete elimination in some cases [67]. While copepods primarily target mosquito larvae, they also feed on other aquatic organisms, which help to maintain ecological balance in water bodies [68, 69]. However, their ability to control mosquito populations might be reduced because they are not exclusively mosquito predators and may consume other organisms [67, 70]. Additionally, only large copepod species (over 1 mm) can effectively prey on mosquito larvae, limiting the range of species suitable for biocontrol [67]. The impact of copepod introduction on nontarget species and ecosystem dynamics requires careful assessment to avoid unintended consequences [71]. Odonata larvae, encompassing dragonflies and damselflies, are voracious mosquito predators, effectively reducing mosquito populations [13]. Their extended larval development makes them ideal biocontrol agents, allowing for continuous mosquito predation [72]. However, this long development period can be a drawback. Dragonfly larvae in temporary ponds may not survive extended droughts, hindering control effectiveness [73]. Additionally, some Odonata larvae exhibit prey preferences, favoring other aquatic insects over mosquito larvae [74]. The research on copepods, dragonflies, and damselflies suggests they could be useful for mosquito control, but there are also some drawbacks like impact on other organisms and long development times.

Toxorhynchites mosquitoes are a promising choice for biocontrol against mosquitoes compared to Copepoda and Odonata (dragonflies and damselflies). They target mosquito larvae specifically, minimizing disruption to the ecosystem. Additionally, their faster life cycle allows for quicker population control compared to Odonata whose development can be slow. These factors make Toxorhynchites a compelling option for eco-friendly mosquito management. These studies highlight Toxorhynchites species as mosquito predators [27, 33, 41, 44, 48, 50]. Among Toxorhynchites species, Tx. splendens stands out for its well-documented success in controlling Aedes larvae, though effectiveness might vary against Ae. aegypti. Tx. amboinensis offers a broader range of mosquito prey but requires study on its ecological impact. Tx. moctezuma shows promise for long-term suppression but may necessitate frequent releases. Tx. rutilus boasts high predation rates but has limitations in target stages and requires careful management to avoid cannibalism. Tx. brevipalpis excels in warm climates and might work well with other control methods, but field data are limited. Tx. violaceus and Tx. towadensis show promise in the laboratory but need real-world testing. While Tx. theobaldi offers an intriguing indirect control mechanism, its predatory impact is less direct. However, the potential of many Toxorhynchites species remains unstudied, offering a wealth of potential for future mosquito control research.

4. Conclusion

Various Toxorhynchites mosquito species exhibit promising potential as biological control agents for mosquito populations, particularly Aedes aegypti, the vector of dengue hemorrhagic fever. Their key strengths lie in their voracious predatory nature and minimal ecological impact. Species like Tx. splendens, Tx. amboinensis, and Tx. moctezuma have demonstrated significant reductions in Aedes populations in both laboratory and field trials. Based on the available data, among Toxorhynchites species, Tx. splendens stands out for its well-documented success in controlling Aedes larvae and Tx. amboinensis appears to be the most suitable species for controlling Aedes mosquito populations due to its high predation rates, effectiveness against various mosquito larvae, and successful field trials. However, limitations exist, including potential variations in effectiveness across habitats and developmental stages, as well as the need for further research on long-term sustainability and potential ecological ramifications. Future research should focus on optimizing rearing and release strategies, exploring combined control methods, and investigating the influence of environmental factors on predation rates. By addressing these limitations, Toxorhynchites species can become a valuable component of integrated mosquito management programs, offering a safe and eco-friendly approach to curbing mosquito-borne diseases.

Data Availability

No primary data were used to support this study. Information presented in this review is based on published papers, which have been duly cited.

Conflicts of Interest

The authors declare that they have no conflicts of interest.

Authors' Contributions

PRS conceptualized the study, proposed the methodology, formulated ideas, performed formal analysis, investigated the study, and wrote the original draft. RCP and TRG supervised the study and reviewed and edited the article, and finalized it.

Supplementary Materials

Supplementary Materials

Supplementary Table 1. Spreadsheet of extracted data.