Biol_71_1

Introduction

Insects are the most diverse groups of animals on Earth, characterized as tracheal arthropods with three distinct body regions, having three pairs of legs, usually one or two pairs of wings although some species are wingless. Despite their immense diversity, their total body mass is smaller than other living organisms on Earth (Yang and Gratton, 2014). Approximately 10% of all known animal species inhabit inland waters, which covers less than 1% of the Earth’s surface. Over 60% of this diversity consists of aquatic insects, with nearly 100,000 species currently identified. While some of these species live in brackish water but majority inhabit freshwater ecosystems are shown in (Table 1).

Diptera, Coleoptera and Hemiptera are semi-aquatic. Approximately 30%, 3% and 10%, respectively of these three orders live whole or some part of their life in aquatic ecosystem (Balian et al., 2008). Mayfly provides both direct and indirect benefits to freshwater ecosystems-streams. It uses as a source of food for fish. Moreover, regulatory and supporting services providing by mayfly are water cleaning, decomposition, nutrient cycling bio-turbation and bio-irrigation (Jacobus et al., 2019). Similarly, food web balance are maintained by Trichoptera. Also, stream bed stabilization is improved by it. On the other hand, it acts as bio-indicators (Morse et al., 2019). Ecological services provide by Plecoptera in freshwater ecosystem are food source, indicators of water quality and mediators of nutrients transfer within the ecosystem (DeWalt and Ower, 2019). Moreover, Megaloptera serve as both prey and predators. Also, it helps in decomposition and nutrients cycling in freshwater (Rivera-Gasperín et al., 2019). However, Diptera are key stone species which act as ecosystem engineers. So, serve as water quality indicators, as bio-control agents, also modifies habitat for themselves or for other organisms (Adler and Courtney, 2019). Also, ecological services performed by different insects’ orders are shown in (Table 2).

Ecosystem services provided by insects in terrestrial ecosystems are successfully explained by various researches. In contrast, significant challenges remain for working on freshwater ecosystem. Investigating the ecological contribution of insects in freshwater-streams could reveal importance of aquatic insects for maintaining food web dynamics and freshwater ecosystem health. This review fills this gap by analyzing relationship between aquatic ecosystems and insects, also emphasis on ecosystem services provided by aquatic insects. By investigating, this study provides new insights into ecological contribution of insects in streams, offering more comprehensive approach towards protection of aquatic insects.

Ecological contribution

Insects play significant role in aquatic ecosystems and maintain balance in natural water bodies by acting as indicators of water quality, break down organic matter and ecosystem engineers. In this way they support biodiversity and maintain resilience of ecosystem.

Table 1: Number of insects species in aquatic ecosystem.

Order	Representative	Habitat	No. of species in aquatic (freshwater)	Reference
Ephemeroptera	Mayfly	Fresh water (lotic)	3046	(Barber-James et al., 2008)
Odonata	Dragonfly, damselflies	Freshwater(lentic and lotic)	5680	(Kalkman et al., 2008)
Plecoptera	Stoneflies	Freshwater(lentic and lotic)	3179	(Fochetti and Tierno de Figueroa, 2008)
Trichoptera	Caddis flies	Freshwater	14291	(De Moor and Ivanov, 2008)
Megaloptera	Fishflies,dobsonflies and alderflies	Freshwater-lotic and lentic	328	(Cover and Resh, 2008)
Neuroptera	Larval stage of spongillaflies, lacewings	Freshwater (lotic and lentic)	73	(Cover and Resh, 2008)
Coleoptera	Diving beetle, water scavenger beetle, marsh beetle, riffle beetle, whirligigs	Freshwater (lotic and lentic)	10,941	(Jäch and Balke, 2008)
Diptera	Larval Mosquitoes, midges, black flies, crane flies.	Freshwater (lentic and lotic)	46,167	(Wagner et al., 2008)
Heteroptera	Water bugs, water striders	Fresh water(lentic and lotic)	4425	(Polhemus and Polhemus, 2008)

T able 2: Services provided by insects in aquatic ecosystem.

Ecological role

Order

Representative

References

Consumer

Ephemeroptera

Trichoptera

Diptera

Mayflies

Caddis flies

Chrysomelidae beetles

(Hershey et al., 2010)

(Thorp and Rogers, 2010)

(Pascal, 2001)

Decomposer

Trichoptera

Diptera

Caddis flies

Chironomid larvae

(Solanki and Shukla, 2015)

(Yan et al., 1991)

Prey

Ephemeroptera

Plecoptera

Trichoptera

Diptera

Megaloptera

Mayflies

Stoneflies nymph

Caddis flies

Aquatic beetles

Dobson flies

(Sangpradub et al., 2014)

(Tierno De Figueroa and López-Rodríguez, 2019)

(Morse et al., 2019)

(Paul and Datta, 2022)

(Rivera-Gasperín et al., 2019)

Predators

Hemiptera

Diptera

Water bugs

Water beetles

(Klecka, 2014)

(Jäch and Balke, 2008)

Biocontrol agent

Coleoptera

Hydrilla tuber weevil

(N. Chaudhri, 2024a)

Habitat Modifiers

Ephemeroptera

Ephemera danica

Mayflies

(CLEMENTE et al., 2018)

(Grzybkowska et al., 2016)

Bioindicator

Diptera

Hemiptera

Ephemeroptera

Chironomid larvae

Backswimmers

Mayflies

(Elango et al., 2021)

(Thaware, 2023)

(Jumaat and Hamid, 2021)

Bioremediation

Plecoptera

Odonata

Stoneflies

Dragonflies, damselflies

(Suter and Cormier, 2015)

(KT et al., 2024)

Nutrient cycling

Diptera

Trichoptera

Water scavenger beetles

Caddis flies

(Ramin et al., 2022)

(Geonka, 2023)

Provide food for other organisms

Aquatic insects provide food as shown in (Figure 1) for several animals, such as aquatic birds (n=9), fishes (n=157), amphibians (n=15), reptiles (n=9), invertebrates (n=22) and semi-aquatic mammals (n=12) (Macadam and Stockan, 2015; Suter and Cormier, 2015). Birds that are found in freshwater habitats, such as the blue duck and grey wagtail, also eat stonefly (Plecoptera) nymphs (Tierno De Figueroa and López-Rodríguez, 2019). Larval megaloptera (alderflies and dobsonfly) serve as a significant component within aquatic food webs forming a dietary source for a variety of organisms, including both vertebrates and invertebrates. Aquatic invertebrate predators of Megaloptera include Odonata naiads and predatory Trichoptera; moreover, other groups such as aquatic Coleoptera and Hemiptera may also consume megalopteran larvae. For fish larvae of alderflies and dobsonfly (Megaloptera), are essential food sources (Rivera-Gasperín et al., 2019).

Trichoptera (caddis flies) serve as food source for fish species. For example, Acipenser fulvescens rely on trichoptera for up to 60% of their diet (Macadam and Stockan, 2015). These feeding interactions between fish and insects represent a typical predator-prey relationship in aquatic environments. This prey-predator dynamic helps regulate insect populations, ensuring balanced species diversity and supporting the energy requirements of higher trophic levels in the food web (Sangpradub et al., 2014). The larval and adult instars of caddis flies (in conjunction with mayflies, stoneflies, dipterans, and several other taxa) are commonly preyed upon by fish. Hemipterans are widely distributed insects capable of colonizing nearly all types of aquatic habitats and frequently represent one of the earliest succession stages in newly formed water bodies, such as artificial ponds (Papáček, 2013). They constitute an important food source for many organisms, including amphibians, waterfowl, and various other animals (Tara and Kour, 2014).

Aquatic Dipterans (blackfly larvae, chironomids) especially larvae, are a vital source of food for a range of vertebrates and invertebrates, whose fitness is proportional to their abundance. Even carnivorous plants are aided by aquatic Dipterans resulting from in-stream pupae. Aquatic dipterans contribute significantly to vertebrates’ diets, such as birds, which inhabit wetlands. For instance, black fly abundance has a direct correlation to harlequin duck production and a lack of chironomids may reduce duckling survival in a multitude of species (Adler and Courtney, 2019). Ephemeroptera (mayfly) are a significant component of many species’ diets due to their abundance. Mayflies are consumed by up to 224 species, including aquatic birds, amphibians, mammals, as well as a variety of other invertebrates, particularly those of the Arachnids and Odonata (Jacobus et al., 2019). Among these predator-prey connections, the role that mayflies play in fish food is arguably the most significant. Freshwater fish are a lifeline for many people worldwide, serving as both food and a catalyst for the local economy. Depending on the species, mayflies contribute different amounts to the diet of freshwater fish. Some fish species depend on mayflies nearly entirely, whereas others eat them incidentally or casually. For instance, mayflies make up 98% of the Oscar cichlid’s (Astronotus ocellatus (Agassiz)) diet (Chordata: Actinopterygii: Cichliformes: Cichlidae)) diet (Jacobus et al., 2019). Mayflies play a crucial role in the energy exchange between primary producers and secondary consumers by being a staple food of fish and other aquatic creatures. Fish or other predators may consume them when they scrape and consume periphyton from submerged surfaces. Higher trophic levels in the aquatic community can access the energy and nutrients found in fine particle organic matter (FPOM) that mayflies collect (Jacobus et al., 2019).

Predators

In an aquatic environment, equilibrium is maintained by predatory insects, they keep prey populations in balance and also control invasive pest populations (Rivera-Gasperín et al., 2019). Aquatic predatory insects efficiently manage the prey populations in India’s Ramala Reservoir (Kulkarni and Zade, 2020). Within streams lacking fish, Corydalidae larvae (dobsonflies and fish flies) can become the largest and most prevalent predator, markedly influencing food web dynamics (Cover et al., 2015). This group typically manages the populations of other invertebrates (Domínguez and Fernández, 2009). Water scorpions (Nepidae), pygmy backswimmers (Pleidae), and water striders (Gerridae) feed on other insects, tadpoles, crustaceans, small fish, and mosquito larvae (Kulkarni and Zade, 2020). Specific families of these bugs can be utilized in the biological control of mosquito larvae (Saha et al., 2007). Hemipterans are among the highly successful colonizers of temporary ponds, and strong selective pressures exist among hemipteran species favoring early migration to temporary ponds during the spring for reproduction, followed by the rapid development of the subsequent generation (Tara and Kour, 2014). The role of Hemipteran predators in regulating mosquito larvae populations was first recognized in New Zealand in 1939 when stock troughs containing Anisops assimilis were observed to be free of mosquitoes, whereas puddles in adjacent depressions contained mosquito populations (Kumar and Hwang, 2006). Dragonfly naiads (Odonata) help to balance lower trophic levels by managing larval populations (Rivera-Gasperín et al., 2019).

Predatory water beetles (Dytiscidae: diving beetle) promote the stability of the food chain at low trophic levels by feeding on mosquito larvae and tiny fish (Saha and Gupta, 2015). Some aquatic insects feed on harmful invasive plants for example, hydrilla tuber weevil (Coleoptera) and water lily beetles (Coleoptera) are used as biological pest control for hydrilla plants and water lily flowers, respectively. As predators, insects contribute to aquatic food webs in a variety of ways. Their presence promotes trophic-level nutrient cycling, population balance, and energy transmission, all of which add to the resilience and stability of aquatic ecosystems (López‐Rodríguez et al., 2018).

Insects’ role in decomposition and nutrients cycling

Aquatic insects are key components of biodiversity and animal communities, helping in organic matter processing and nutrients back to the aquatic ecosystem. Dytiscidae (water diving beetles), and hydrophilic (giant water scavenger beetles) feed on decaying plant and animal matter, breaking them and releasing nutrients back into the aquatic ecosystem (Ramin et al., 2022). Megaloptera (alderflies, dobsonflies, fish flies) larvae are a common presence in clean lakes, ponds, and various watercourses. Across diverse freshwater habitats, these insects constitute a significant element, playing a crucial role in energy transfer, the recycling of materials, and food webs. Possessing specific traits, especially at high densities, they function as a vital component in trophic relationships, helping sustain aquatic communities’ equilibrium (Rivera-Gasperín et al., 2019).

Bioturbation and bioirrigation process facilitates insects in nutrient flow through aquatic ecosystems. These processes increase nutrient availability, also influence on primary production, and enhanced sediment water exchange of aquatic ecosystems. For example, chironomid larvae (Dipterans) serve as surface and filter deposit feeders. The ratio of electrons acceptors into sediments increases by larvae that are constantly pushing water into underlying sediments. As a result, larvae enhance the depth at which oxidative reaction decomposition occurs. Filter feeding larvae also help in mixing of water layers. The nutrient distribution and growth of phytoplankton are also disturbed by the mixing of these water layers.

Caddis flies (Trichoptera) produce proteinacous silk by its silk glands. Silk produced by caddis flies (Trichoptera) larvae adheres to various surfaces underwater, such as rocks and plants. Plants which are covered by silk help in stabilizing sediments and reduce erosion. Nutrients exchange between water and plants also take place by silk. Through the processes of ammonification and decomposition, aquatic insects help in the cycling of nutrients. Caddis flies (Trichoptera) release nitrogen and phosphorus which are essential for the growth of aquatic plants, algae, and phytoplankton when their bodies decompose and return organic matter to the ecosystem. Nutrient cycle increase overall productivity in aquatic ecosystem by providing necessary elements to primary producers (Morse et al., 2019).

Symbioses and insects

Each microorganism is a symbiotic organism community that functions as its own ecosystem. These symbiotes range in size from tiny unicellular forms (e.g., bacteria and protozoa) or smaller (e.g., viruses) to larger forms that are similar in size to the host. In aquatic ecosystem insects and microorganisms such as bacteria, fungi, and algae can develop a variety of symbiotic associations as shown in (Figure 2).

These interactions play significant role in maintaining ecosystem health. Beneficial gut bacteria which help in break down organic materials are frequently present in aquatic insects. For instance, gut bacteria of mayflies (Ephemeroptera) help in the breakdown of plant matter, promoting the insect’s nutritional intake and increase the ecosystem’s nutrient cycle (Geonka, 2023).

Caddis flies (Trichoptera) also make symbiotic association with fungi, which aid in the decomposition of plant materials. These interactions between insects and microbes are essential for recycling nutrients and breaking down organic materials, which ultimately promotes primary production and preserves ecosystem equilibrium. These interactions also sustain other creatures in the food web and increase biodiversity (Geonka, 2023).

Parasites are significantly underrepresented among aquatic Dipterans. Chironomid larvae are commonly seen on aquatic macro invertebrates. In many cases, the connection is simply one of opportunism or phoresy (e.g., Tonoirocladius on Neocurupira), while in others, such as the genus Nanocladius, the relationship is parasitic. Some chironomid larvae live in the cocoons of other Dipterans, such as the Simuliidae, and devour the pupa host, occasionally pupating within the host cocoon (Adler and Courtney, 2019).

In contrast, there are few occurrences of aquatic Dipterans infected with insect parasitoids. Ephydridae are the most likely aquatic Dipterans to contain hymenopterans parasitoids, followed by Sciomyzidae, Stratiomyidae, and Tabanidae. However, aquatic diptera host a wide range of additional symbiotic creatures. Nearly 200 nonbacterial parasite and pathogen species have been identified in larval black flies. Mosquitoes alone have about 150 microsporidia species.The bacterial community on and in aquatic Dipterans are remarkably diverse, varying by species, life stage, and gender. The host likely requires the bulk of the bacterial species. Thus, aquatic Dipterans provide ecological benefits through a packed ecology of varied microorganisms that drive many of the host dipterans processes (Adler and Courtney, 2019).

Ecological indicators of healthy ecosystem

Bio-monitoring is the assessment of environmental health by using biological responses. In aquatic ecosystems, insects are used to determine water quality and ecosystem health due to their diversity, life stages, sedimentary nature, and ability to survive in any ecosystem help them accurately identify and quantify the disturbance that is affecting water quality and ecosystem health. Communities of aquatic insects in streams of sekayu indicate excellent water quality. Aquatic insects also play a significant role in indicating habitat disruption due to anthropogenic and natural activities in riverine potholes, Kerala, India (Athulya et al., 2024; Baskar and Gawade, 2021).

Ephemeroptera (mayflies) presence indicates the trophic or productive state of running water. Its abundance indicates an oligotrophic condition. When several mayfly species are rare, it indicates a mesotrophic condition. Aquatic insects such as mayflies are very sensitive, and they immediately respond to changes in environmental conditions such as accumulation of micro plastic (Jumaat and Hamid, 2021). For example, when the water temperature rises, then mayflies respond to such change by decreasing their size (Sweeney et al., 2018). When pH level changes, mayflies show changes in shape, functioning, and behavior (Peterson et al., 1985), the capacity of aquatic insects, such as mayflies, to react to environmental changes provides an early warning system for water quality, which benefits the ecosystem.

Aquatic insects are good indicators of water pollution. For example, the excessive number of Plecoptera indicates clean water. Stoneflies are among the most pollution-sensitive aquatic insects, yet they have a wide range of sensitivity, allowing a limited number of species to survive in even severely polluted streams. Certain corixid species are used as indicators of water quality, and research indicates that the quality of the aquatic environment is partly contingent upon the abundance of bug populations (DeWalt and Ower, 2019).

The abundance of nymphs of damselflies (odonata) indicates moderately polluted water (Elango et al., 2021; Thaware, 2023). The abundance of chironomids (coleoptera) indicate extremely polluted water (Thaware, 2023). Insects are also used to detect heavy metals present in water bodies. Heavy metals are uranium, mercury, and selenite (Mo et al., 2013). For example, dragonflies (Anisoptera) and damselflies (Zygoptera) quickly respond to heavy metal accumulation and facilitate knowing about ecosystem status (KT et al., 2024).

Aquatic insects are good water-quality indicators. As canaries in the coal mine, they often give the first warning when an aquatic environment is polluted or harmed. The Dipteran (chironomidae and meniscus midge larvae) is often employed in bioassessment schemes and is a standard component of Environmental Protection Agency rapid bioassessment protocols. Due to their number and variety, Ephydridae and Sciomyzidae have been considered to be dipterans of vital significance to North American freshwater wetlands (Adler and Courtney, 2019).

The vital roles that aquatic insects particularly mayflies (Ephemeroptera) play in aquatic ecosystems, their sensitivity to change, and our growing capacity to collect and identify them have made them a valuable tool for monitoring freshwater quality along with other macro invertebrates. Mayflies meet the criteria for good indicators because they are abundant and sufficiently diverse in their habits and habitats, sensitive and predictable in their response to changes in environmental conditions, relatively easily sampled and identifiable to meaningful taxonomic resolutions, and bioaccumulation chemicals, allowing the pathways of toxins in the environment to be traced (Jacobus et al., 2019). As biological indicators, their reaction to changing conditions is integrated over time and place, potentially reducing sampling labor and expense when compared to the high intensity of sampling necessary when relying on chemical variables to detect specific impacts (Jacobus et al., 2019).

Their broad ranges of functional traits and differential tolerances to anthropogenic factors have been widely noted and are either used, or have the potential for use, in the development of biotic indices to monitor agricultural practices, organic pollution, eutrophication, acidification, pesticide pollution, physical habitat alteration Mayflies also react to temperature variations.Aquatic insects have been utilized as biosentinels to monitor levels of a range of heavy metals, including methyl mercury, mercury, selenite, and uranium in freshwater environments. Larvae, in particular, are susceptible to low nitrate levels in water, as well as variations in phosphorus. One study found that phosphorus enrichment boosted mayfly development rates (Jacobus et al., 2019).

Ecosystem engineers

Aquatic insects play significant roles as ecosystem engineers in freshwater habitats. These insects modify their surroundings in different ways that influence biodiversity, water quality, and nutrient cycling, ultimately stabilizing aquatic ecosystems and supporting ecological functions (Tumolo, 2022). The labial silk-producing organs of caddis fly larvae (Trichoptera) are considerably developed, extending posterior and occupying a significant portion of the abdominal cavity thereby facilitating the synthesis of substantial quantities of proteinaceous fibroin and sericin filaments, exhibiting similarities to those produced by Lepidopteran larvae. Nevertheless, the silk generated by caddis fly larvae, in contrast to that secreted by their lepidopteran relatives, exhibits adhesive properties in submerged environments. This characteristic has spurred significant investigation into the attributes of caddis fly silk, identified as an exceptional origin of design concepts for robust, self-repairing artificial substances, filaments, and textiles, particularly well-suited for submerged and hydric biomaterial applications, as well as biomimetic methodologies for extruding water-soluble polymers into fibers under aqueous conditions (Morse et al., 2019).

Caddis flies (Trichoptera) perform filtering activities that remove fine particulate organic matter (FPOM) from water by the process of suspension. In this way, it regulates its movement downstream. Hydropsyche siltalai Döhler upstream species by using its net-like filter clear 492 liters of water per day. Under eutrophic circumstances, the larval stages of resilient species such as Hydropsyche contubernalis McLachlan, 1865, can proliferate in considerable abundances, reaching up to 10,000 individuals per square meter exhibiting the capacity for sequestering and eliminating significant quantities of organic material from suspension. Larvae adjust its net topology at moderate to high densities, also stabilizing sizes of particles passing through net. By removing suspended particles, these nets help in preserving water quality. Hydropsyche contubernalis McLachlan which is downstream specie, use its silk retreat to remove large quantity of fine particulate organic matter from water (Morse et al., 2019).

A further ecological benefit conferred by rheophilic caddis flies that construct capture nets resides in their contribution to the consolidation of the streambed through the adhesion of inorganic substrates via their secreted silk. By employing silk filaments affixed to sedimentary particles, these invertebrate ecosystem engineers impede the displacement of sediments and generally attenuate sediment transport, consequently diminishing physical disturbance to benthic organisms during periods of elevated flow, and ensuring substratum integrity even under typical environmental circumstances. In close proximity to the streambed, within the reduced current velocity zones created by caddis fly filter nets, other bottom-dwelling macro invertebrates discover sanctuary in diminished flow regimes. They are also recognized as habitat modifiers and have applications in forensic science (Morse et al., 2019).

In the context of food webs, caddis fly larvae, akin to many aquatic insects, process organic matter that is inaccessible to other components of the ecosystem. A key example involves shredding detritivores, which fragment large (>10µm³) particles of decaying organic matter (CPOM) from various sources using their mouthparts, digest the microbial biofilm on these particles, and absorb the available nutrients. While less common, some larvae act as primary consumers, feeding on living plant material through shredding or piercing mechanisms, with both feeding strategies resulting in the egestion of fecal pellets (Morse et al., 2019). Fragmented matter generated during the comminution process or expelled as excreta becomes accessible to detritivorous organisms capable of acquiring minute particles (less than 10 cubic micrometers; designated as “fine particulate organic matter” or FPOM), either by accumulating it from the substratum or by sieving it from the aqueous medium. The biomass of these primary consumers subsequently serves as nourishment for predatory fauna, which also discharge waste products into the surroundings (Morse et al., 2019). Consequently, caddis fly larvae and other insect taxa, through their specialized feeding mechanisms, exploit available nutrients in their various states and, in turn, contribute to the availability of these resources for a wide spectrum of organisms occupying distinct trophic levels within freshwater ecological systems (Morse et al., 2019).

Mayflies provide numerous crucial services that maintain and optimize ecosystem function. Burrow-dwelling species such as Hexagenia limbata (Serville) (Ephemeridae) (Michigan Hex), Ephemera danica (Müller) (Ephemeridae), and Campsurus violaceus Needham and Murphy (Polymitarcyidae) both bioirrigate and bioturbate by reworking sediments in rivers and flowing water through burrows. One study, determined that as much as 98% of sediment disturbed in Lake Saint Joseph, Canada, was due to H. limbata. In an additional study Hexagenia spp. bioturbated and bioirrigated Lake Erie and this resulted in an influx of soluble reactive phosphorus in water. Mayflies can transport nutrients both within and among aquatic ecosystems. This could be crucial for preserving diverse aquatic communities, particularly if different climatic projections come to pass (Jacobus et al., 2019).

Certain mayfly migrations may increase the resilience of cool-water carnivores in warming river networks by transferring food subsidies from productive but warming river main stems to cool but food-limited tributaries. Such migrations have been demonstrated for Ephemerella maculata Traver (Ephemerellidae), and they were more crucial to the early development of a trout species than terrestrial invertebrate subsidies. Whereas every species impacts its immediate surroundings to some degree, some species make a much larger impact at a whole-habitat level. The size of their impact is often related to their population numbers. Some aquatic Dipterans, for instance, act as ecosystem engineers organisms that strongly modify their environment, and thereby impact other organisms’ ecological processes and dynamics. The term keystone species refers to organisms that have a vital role in sustaining ecosystem functioning and community structure and that have an impact large and disproportionate to their prevalence. Suspension feeding larvae Dipterans help to maintain biological materials in lentic and lotic environments (Adler and Courtney, 2019).

Bioturbators refer to organisms that burrow, feed, and defecate to churn and condition sediments. It can mobilize many chemicals and nutrients by their activities, making them available to other organisms. Bioturbators can be found among aquatic Dipterans. Chironomid larvae have been known to exist in colonies of as many as 150,000 individuals per square meter and feed on rotting organic detritus and defecating; these processes provide much aeration and nitrogen to the environment, and it changes both animal and plant population (Adler and Courtney, 2019). Suspension feeders like black flies filter small particles, colloids, and dissolved organic substances, and compress these materials into fecal pellets and transport them downstream. The pellets act as repacked organic matter that acts as fodder to microbes and macro-invertebrates, either when in transport, or following deposition. The daily transport of fecal pellets of larval simuliids along a line along some rivers amounts to an astronomical 429 tons of dry mass equating to about as much as 6000 elephants defecating (wet weight) into the river every twenty-four hours (Adler and Courtney, 2019).

In still water bodies like natural pools and ponds, mosquito larvae generate a constant rain of fecal pellets that sustain other organisms’ diets. Carbon and nitrogen-rich pellets act as an important substrate to bacteria and biofilm growth, enriching the aquatic food web and supplying nutrients to rivers and floodplains. Larval black flies also produce adhesive silk that traps minute colloids and particles, keeping organic matter within the system. Their silken cocoons catch debris and provide refuge to other macro invertebrates. Thus, aquatic Dipterans’ silk, e.g., simuliids, controls periphyton growth and encourages tufa formation. Scrapers (grazers), strip surfaces of attached materials and periphyton, making it possible for other organisms to colonize. Populations of as many as 1,000 blepharicerid larvae per square meter have been reported to successfully clear extensive areas of rocky substrate and in this way play significant role as bioremediation (Adler and Courtney, 2019).

Bio-control agent

Invasive plant species have proliferated and taken over aquatic environments as a result of urbanization and habitat change, upsetting natural biodiversity and ecological stability. As biological control agents, aquatic insects are essential for controlling the spread of noxious, non-native plants and re-establishing the equilibrium of ecosystems as shown in (Grutters et al., 2016).

Thysanoptera act as biological control agent. For example, the alligator weed thrips (Amynothrips andersoni), play significant role in controlling the alligator weed that is an invasive plant in the United States. These insects by consuming the alligator weed, play significant role in reducing alligator weed damage to natural plants (Elango et al., 2021). Water hyacinth weevil (Neochetina eichhorniae) control water hyacinth expansion by consuming its tissues and preventing it from growing and reproducing. This reduces the thick mats create by water hyacinth that would otherwise retard water movement, lower oxygen levels, and harm aquatic environments (Chaudhri et al., 2024).

Moth species Paraponyx stratiotata (ringed china moth larvae) also acts as a biological control agent. It restricts the spread of invasive plants by consuming the leaves and stems, which directly affects the plant tissues and reduces their reproductive capacity, especially during the growing season. The role of these insects as biological control agents is significant not only for reducing invasive species but also for supporting biodiversity and maintaining ecosystem balance. By keeping the populations of non-native plants in balance, these insects contribute to healthier aquatic ecosystems and retards from the competitive exclusion of native plant species, that supports a balanced aquatic environment (Grutters et al., 2016).

Aquatic Dipterans have been widely used as biological control agents both as insects that prey on tissue-feeding pests and disease vectors, and as herbivorous insects attacking aquatic plants. The group Toxorhynchites (elephants mosquito) has in excess of 90 giant mosquito species that as adults are unable to cut tissue in order to suck blood and as larvae feed on other mosquitoes. Toxorhynchites have been employed as biological control agents against pest and vector mosquitoes since over a century ago, with mixed results. While, not extensively used in biological control, larvae of seven aquatic Diptera orders have exhibited predatory activity against larvae of black flies. Larval Sciomyzidae (marsh flies) are obligate snail parasites or predators, and snails act as intermediate hosts to trematode parasites, the cause of human and animal schistosomiasis (bilharzia) and fascioliasis. Their potential as biological control agents is so considerable, and there has been some field success; increased dependence on sciomyzids is expected as resistance to antihelminthics and worries about chemical use in wetlands grow (Adler and Courtney, 2019). Herbivorous aquatic Diptera have potential as biological control agents for toxic aquatic plants. Specialized algal feeders from the Ephydridae could be utilized as biological control agents if the algae develop rapidly. Hydrellia ephydrids (hydrilla leaf mining flies), which feed on plants by mining them, have been successfully used as biological control agents of marsh hydrilla weeds.

Aquatic insect as vector of fish pathogen

Aquatic insects play important role in carrying vector pathogens i.e. parasites, bacteria, and viruses with their bodies and transferring these pathogens to fish bodies through contact or ingestion process. In this way, insects act as vector for fish infection. Fish are infected by Aeromonas bacteria that cause aeromoniasis in fish. Aquatic insects such as water beetles and midges (Chironomidae) may harbor Aeromonas bacteria in their digestive systems or on their body surfaces. Fish can become infected with these bacteria when they come into contact with or consume these insects, resulting in illnesses that cause ulcerations, hemorrhaging, and, in severe cases, significant mortality rates in fish farms and natural environments (Al-Saffar and Ghazwan, 2021).

Conclusion

Aquatic insects play indispensable roles in maintaining the stability and health of freshwater ecosystems. As decomposers, prey, and predators, they facilitate nutrient cycling and support complex food webs. By regulating populations across trophic levels, they enhance ecosystem resilience and biodiversity. As bio-indicators, they assess water quality response to changes in water chemistry and temperature. In this way, they serve as early warning tools for ecological disruption. Furthermore, their roles as ecosystem engineers enable the stabilization of sediments and enhancement of water oxygen levels, which benefits a wide range of aquatic organisms. Additionally, aquatic insects manage pest population in freshwater ecosystem. Despite their ecological important, these insects are increasingly threatened by environmental pollution, habitat loss, and climate change. Protecting aquatic insects is crucial for the conservation of freshwater ecosystems. Future research should focus on understanding how anthropogenic impacts such as climate change those changes mixing-stratification regimes which in return alter water quality, fisheries productivity, and escalated increase in green house gases release, abrupt disturbance in biogeochemical cycle and prominent decrease in biodiversity by inhabiting primary production. Moreover, it increases organic matter decomposition through photo degradation affect their ecological function. Conservation efforts aimed at aquatic insects will ultimately contribute to the broader health and resilience of freshwater habitats.

Recommendations

Today, individuals spend more time on electronic media and less time engaging with natural environments including streams, ponds, and rural forests. Similarly, academic institutions are increasingly emphasizing molecular methods over the study of living organisms in their natural environment. As a result, fewer students pursue careers in biodiversity research; only entomologists continue to identify insect species, assess their ecosystem services, harmful impacts, needs, and threats. This decline in biodiversity research is significantly leading to unnoticeable extinction of several ecologically and economically important insect species. Therefore, it is necessary to increase career opportunities in biodiversity and place more emphasis on biodiversity education to safeguard these valuable species. Furthermore, project on eDNA metabarcoding of aquatic insects in freshwater ecosystems should be done by researcher to access their diversity and taxonomy in complicated ecosystem. Insects need our protection, and we need their contribution to maintain the integrity and balance of the ecosystem.

Acknowledgments

The first author thanks for kind support for this review to Dr. Mubashar Hussain.

Novelty Statement

This study highlights the overlooked role of aquatic insects in maintaining freshwater ecosystem health, linking their ecological functions to broader impacts like greenhouse gas release and changes in water quality driven by climate change. It offers a fresh perspective on how altered mixing and stratification patterns affect insect roles, emphasizing their value in ecosystem monitoring and conservation.

Author’s Contribution

IA and MH conceived the idea and drafted the article.

AF make diagram using bio-render software.

SS make tables.

SF, MK, IB, AS, MS, UZ and IZ proof read and edited the final version of article.

Conflict of interest

The authors have declared no conflict of interest.

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