The biomass of An. gambiae s.s . mosquitoes present in space and time has two strong correlates: the availability of standing water for larval development, and host availability for bloodmeals and egg maturation. The first drives a strongly seasonal pattern of abundance across much of the sub‐Saharan range and the second influences the spatial dispersion of mosquitoes in and around human habitations and villages (Sinka et al ., 2012 ; Yaro et al ., 2012 ).

Maturation in both sexes, and feeding and resting in males, are largely disaggregated activities that reduce the predictability of adults as a resource to predators. Additionally, adults are harder to locate and catch relative to larvae and are of low resource value compared with other flying prey such as Lepidoptera (butterflies and moths) (Gonsalves et al ., 2013 ). Much of 20th century vector control success with ITNs and IRS was based on post‐mating aggregation in females as they sought to feed on sleeping humans and then to rest in houses. Another period in the adult stage during which anopheline mosquitoes are concentrated as a resource occurs during swarming activity at twilight. Males aggregate above specific, visually contrasting markers and females enter these swarms to find a mate (Diabaté et al ., 2011 ). A large swarm of 1000 mosquitoes can contain approximately 0.2 g of mosquito biomass, and in such concentrated groups some predation of the adult stage by dragonflies is observed (Yuval & Bouskila, 1993 ).

During the larval and pupal stages, biomass is restricted to the water bodies in which the eggs hatched and, at this time and especially in small water bodies, can be concentrated at high densities. High density and site‐specific factors contribute to low survival overall and high mortality in all developmental stages (Koenraadt et al ., 2004a a; Munga et al ., 2007 ).

As with all dipteran species, anopheline mosquitoes have a fully metamorphic (holometabolous) lifecycle. Winged adults mate, after which the female seeks a bloodmeal from a vertebrate host [generally human (Garrett‐Jones et al ., 1980 ; Githeko et al ., 1994 )] with which to mature and develop her eggs. Females oviposit in usually shallow and often temporary water bodies and the eggs hatch into the larval stage. Development from egg to adult via aquatic larval and pupal stages is temperature‐ and environment‐dependent and takes 10–25 days (Bayoh & Lindsay, 2003 ). After pupation, the adult emerges to mature and feed on nectar before mating (Service & Towson, 2002 ). The lifespan of the adult Anopheles mosquito is a few weeks for males and typically less than a month for females, although recent evidence of aestivation in An. coluzzii suggests this may be substantially longer during a dry season (Lehmann et al ., 2010 ; Dao et al ., 2014 ).

Predators

Ecologically, predators may be described as ‘specialists’ (monophagic/stenophagic) or ‘generalists’ (polyphagic/euryphagic) based on whether their natural diets are ‘narrow’ or ‘broad’. Although such studies are rare, to understand the degree of association between any predator and either or both larval and adult An. gambiae, any investigation should seek to reflect the broader diet of the predator. The studies identified and included here, are, in the majority, observations and literature reviews that help to provide a balanced description of potential predatory paradigms. There are also some ‘no choice’ laboratory tests that investigate preference in terms of whether predators will or will not eat various life stages of An. gambiae. There are semi‐field tests that attempt to overlay some aspects of a natural habitat, but these experiments offer either no choice or only one other option. A few more complex field and laboratory trials have attempted to observe, under controlled conditions, the behaviour of predators with a variety of prey. There are also field captures of wild predators that identify the presence of An. gambiae s.l. in the gut. These are positive or negative responses with little information on volume ingested.

The available literature provides an overview of the published ecological relationships of An. gambiae s.l. The diet of mosquitoes as juveniles and adults has not been explored here.

Predation of larvaeThe natural enemies of mosquito larvae are many and diverse, and include insects, spiders, hydras, planaria, copepods, bats, birds and fish. Munga et al. (2007) identified seven families of mosquito predator in larval habitats, including Hydrophilidae (Coleoptera, water scavenger beetles), Dytiscidae (Coleoptera, diving beetles), Corixidae (Hemiptera, water boatmen), Nepidae (Hemiptera, water scorpions), Notonectidae (Hemiptera, backswimmers), Belostomatidae (Hemiptera, giant water bugs) and Cordulidae (Odonata, dragonflies). There are reports that combinations of predatory invertebrates can account for more than 90% of the natural mortality of immature stages of mosquitoes in some aquatic environments (Service, 1971, 1973, 1977).

Much of the literature on larval predation comes from the context of biological control of mosquitoes; many species have been proposed as possible contributors to this, but the oviposition choices of female An. gambiae affect predator encounter rates substantially. Anopheles gambiae s.l. larvae occur in a great variety of habitats, but the most important are small, shallow, sunlit and usually temporary pools (Minakawa et al., 2004). Because of the small size and transient nature of many of these water bodies, few predator species successfully colonize them and habitat stability is low in smaller habitats such as cattle hoof prints, ruts and swales. Environmental and bottom‐up effects, such as evaporation, flushing and reduced food sources in ephemeral opportunistic habitats may be stronger effects as the predation mortality of An. gambiae larvae in these habitats is likely to be relatively low. The most important invertebrate predators in temporary pools are likely to be turbellarian. Turbellarians (free‐living flatworms) assume an importance in ephemeral ponds because they can produce resting eggs that survive dry periods (Blaustein & Dumont, 1990). They are present and become active within the first few days of rains, whereas most other invertebrate predators become effective only later in the hydro‐period of individual pools or at later stages of the rainy season. The relative importance of predation and habitat effects are supported by higher larval survivorship (35–51%) in artificial, semi‐natural habitats not yet colonized by predators (Munga et al., 2006).

Marshes, rice fields, borrow‐pits and wells are examples of larger and more permanent larval habitats. These can support a variety of both invertebrate and vertebrate predators (Service, 1971, 1977). In rice fields, both predator densities and Anopheles spp. survivorship were found to vary greatly through the cropping season (13.4–84.5%); water depth, rice height and predation were primary contributors (Chandler & Highton, 1976).

By creating life tables, Service (1971, 1973) estimated overall larval mortality, from multiple sources including competition and predation, of 97.1% and 96.6% in stable ponds, which are similar to the mortality rates of 95.2% and 96.6% recorded previously in a marsh and pools. Samples of surface and aquatic larval predators found were tested using a precipitin reaction to identify ingestion of An. gambiae. Lycosid spiders (Arachnida, wolf spiders), Muscidae (Diptera, houseflies) and Coleopterans (beetles) were present in all habitats and large proportions tested positive. Of truly aquatic fauna, Odonata (dragonflies and damselflies) were not found in the more temporary habitats such as small pools and ditches, and, furthermore, did not test positive in any reactions (Service, 1971, 1973). Conversely, a later study found nine different species of Odonata, of which five responded positively for An. gambiae (Service, 1977). Similar An. gambiae overall larval mortality rates exceeding 93%, 95% and 98% in drainage ditches, cow hoof prints and disused goldmine habitats, respectively, have been estimated (Munga et al., 2007).

Polymerase chain reaction (PCR) analysis has also been used to determine whether mosquito predators in wetland habitats feed on An. gambiae s.l. larvae and, in one example, showed that, of 330 potential individual predators, 54.2% had ingested An. gambiae. The highest incidence of consumption was in Odonata (dragonfly larvae) (70.2%), followed by Hemiptera (water boatman bugs) (62.8%), Amphibia (tadpoles) (41.7%) and Coleoptera (beetles) (18.0%) (Ohba et al., 2010). Some of these tests can be influenced by the metabolic rate of the test subject. Schielke et al. (2007) used an optimized PCR technique with which intergenic spacer (IGS) ribosomal DNA (rDNA) of An. gambiae s.l. could be detected for longer after ingestion by Lestidae (Odonata, damselflies) after 4 h, by Libellulidae (Odonata, dragonflies) after 6 h, and by Notonectidae (Hemiptera, backswimmers) after 24 h.

The larvae of An. gambiae s.l. are thus consumed by a wide variety of predators. Literature available on this predation is presented by taxonomic order.

Flies (Diptera) Several species of shore fly (Ephydridae) are aquatic predators and have been reported to eat Anophelines (Minakawa et al., 2007). Experiments on prey choice in Ochthera chalybescens (Diptera: Ephydridae) suggest that prey larval stage and size do not affect predator capacity. Younger larvae spent more time near the water surface than did older larvae during experiments, and this behaviour increased the time for which they were exposed to predators. Older larvae can dive deeper, a behaviour that is considered a predator avoidance mechanism (Tuno et al., 2007). The larger size of older larvae, however, may draw more attention from predators and may offset the shorter time they are exposed near the water surface. Thus, both small and large larvae have some advantages and disadvantages in avoiding predation by O. chalybescens. An additional subtlety lies in their low capture rate of mosquito pupae, possibly because of relative immobility in this life stage (Minakawa et al., 2007). Early studies found Ochthera brevitibialis preying on anopheline mosquito larvae and bloodworms. This species of shore fly was sometimes sufficiently numerous to reduce local populations of Anophelines, but had no effect over a larger area. The Anophelines were observed to be easier to catch than Culex spp. in deeper water as the latter were able to escape more readily (Travis, 1947). The Chaoboridae, commonly known as phantom midges or glassworms, have aquatic larvae and feed largely on small insects including mosquito larvae and crustaceans such as Daphnia (Cladocera: Daphniidae). There is no evidence that this predator specializes on mosquitoes (Bay, 1974).

True bugs (aquatic Hemiptera) Hemiptera are mostly herbivorous and use their straw‐like mouthparts to inject enzymes into plants. These digest plant material, allowing the insect to suck the liquefied food back through its mouthparts and into its digestive tract. A few species of Corixidae (water boatmen) are predatory. These are generalist predators in aquatic insect communities, have great plasticity in prey choice and can remain abundant in varied resource environments (Symondson et al., 2002). Several studies have proposed aquatic hemipterans as potential mosquito control agents (Darriet & Hougard, 1993; Ohba & Nakasuji, 2006; Sivagnaname, 2009; Saha et al., 2012). Ohba & Nakasuji (2006) investigated feeding habits of Nepoidea (Belostomatidae, water bugs, and Nepidae, water scorpions). They collected dietary items in wetlands and obtained data from the published literature that showed a broad diet. These species are also effective predators of medically important pests, such as snails, and mosquito larvae (39.3% of diet was insect, of which a proportion was mosquito). Examinations of the DNA of gut contents of invertebrate and vertebrate taxa in Kenyan wetlands revealed Nepomorpha (true water bugs) to be greater consumers of mosquitoes of human importance than were amphibians (Ohba et al., 2010). The major diet items of Lethocerus deyrollei (Vuillefroy) (giant water bug) (Hemiptera: Belostomatidae) and Laccotrephes japonensis (Scott) (water scorpion) (Hemiptera: Nepidae) are tadpoles, but L. japonensis nymphs also feed on aquatic insects, including mosquito larvae. The dominant feeding strategy in this taxon is predaceous, but several species consume other foods, particularly algae and detritus (Hadicke et al., 2017). Jansson & Scudder (1972) observed Cymatia sp. (water boatmen) (Hemiptera: Corixidae) to capture mosquito larvae. Hale (1922) kept several Australian species of Corixinae (water boatman) in aquaria for months, and during that time fed them only with larvae of Culex quinquefasciatus and Scutomyia notoscripta (Diptera: Culicidae) mosquitoes. Newly hatched Corixinae captured early‐instar larvae and increasingly larger individuals during successive stages of metamorphosis. Saha et al. (2010) investigated the prey electivity and switching dynamics of predatory heteropteran water bugs Anisops bouvieri (Hemiptera: Notonectidae), Diplonychus rusticus (Hemiptera: Belostomatidae) and Diplonychus annulatus in the laboratory under various prey densities using mosquito and chironomid prey. Anisops bouvieri and D. rusticus consume mosquito larvae under many circumstances but can readily forage on other prey when mosquito densities are low. In India, the giant water bug Diplonychus indicus is a voracious predator of mosquito larvae, tadpoles and juvenile fish, with a preference for both anopheline and culicine larvae. A single water bug may consume 300 larvae per day (Venkatesan et al., 1986). Munga et al. (2006), studied the effects of predator and competitor presence on the oviposition rates of An. gambiae in the laboratory. Rainwater was either conditioned, or not, with a backswimmer or a tadpole; and mosquitoes laid fewer eggs in conditioned than in unconditioned rainwater. Intraspecific competition tests showed that more mosquito eggs were laid in containers with five conspecific larvae than in those with higher densities (40, 70 or 100 larvae). Warburg et al. (2011) also found that when offered deionized water and deionized water conditioned with Notonecta maculata (Hemiptera: Notonectidae), gravid An. gambiae females preferentially oviposited into the predator‐free option.

Dragonflies and damselflies (Odonata) Adult dragonflies are conspicuous predators of mosquitoes and are sometimes termed ‘mosquito hawks’. Most studies, however, have focused on larval predation. In field surveys of predators in Kenya (Service, 1973, 1977), serological studies of the gut showed that none of the larval Odonata tested positive for mosquito prey in 1973 and only half of the species tested positive in 1977. Ischnura senegalensis (Odonata: Coenagrionidae) was the most common mosquito feeder, with 47% testing positive for An. gambiae. Saha et al. (2012) evaluated the predation potential of larvae of the damselfly Ceriagrion coromandelianum (Odonata: Coenagrionidae) and the dragonfly Brachydiplax chalybea (Odonata: Libellulidae) under varied habitat conditions. Odonate larvae were exposed to different densities of Cx. quinquefasciatus larvae in small water‐filled containers and then large containers with vegetation that provided a semi‐field environment. The presence of vegetation reduced predation of mosquito larvae by both species, possibly because plants reduce the effective space available for prey–predator interaction and serve as a refuge that reduces prey vulnerability (Saha et al., 2012). Studies of the foregut contents of field‐caught juvenile Enallagma civile (Odonata: Coenagrionidae) damselflies revealed they had fed predominantly on chironomid larvae. Corixid, cladoceran, ostracod and aquatic mite remains were also found in some specimens examined. However, no remains of mosquito larvae were detected in any specimens, although mosquito larvae were observed as continuously present in sample pond sites (Breene et al., 1990). Although odonate larvae are widely considered to be voracious predators of mosquito larvae, this is not supported by the available literature. They are true generalist predators with a wide range of dietary choice (Corbet, 1980).

Shrimps and other Crustacea The presence of the tadpole shrimp Triops granarius (Notostraca: Triopsidae) was coincident with low numbers of An. gambiae larvae in temporary pools around huts in a village in Somalia (Maffi, 1962), although it was not clear whether this reflected avoidance, predation or competition. Laboratory oviposition choice tests and behavioural observations indicated that the activity of the tadpole shrimp Triops longicaudatus near the water surface deterred gravid Cx. quinquefasciatus from ovipositing (Tietze & Mulla, 1991). Consequently, Triops spp. are considered both effective larval predators and mosquito oviposition deterrents (Fry et al., 1994). Field surveys of Anopheles, floodwater Aedes and Culex breeding habitats have shown that natural copepod populations can substantially reduce, or even eliminate, mosquito production. Field trials in temporary pools, marshes and rice fields have demonstrated that the introduction of the right copepod species to the right habitat at the right time can eliminate Anopheles or floodwater Aedes larvae. Cyclopoid copepod predators consume protozoans, rotifers and small aquatic animals such as first and second instar mosquito larvae (Marten et al., 1994; Marten & Reid, 2007).

Spiders (Arachnida) Spiders feeding in and around aquatic habitats have a diverse array of strategies; most spiders that predate on mosquito larvae are active hunters that do not build webs. These spiders can be terrestrial, standing at the water's edge, semi‐aquatic, surface film locomotors or subsurface divers that use air sacs. Using the serological method, Service (1971, 1973, 1977) identified several predators of An. gambiae in western Kenya, among which, wolf spiders (Lycosidae) were important consumers of newly emerged adults. By contrast, Perevozkin et al. (2004) found that spiders belonging to the genera Dolomedes (Araneae: Pisauridae) and Argyroneta (Araneae: Cybaeidae) actively preyed upon anopheline and culicine larvae, but wolf spiders [Pardosa spp. (Araneae: Lycosidae)] did not. Perevozkin et al. (2004) then conducted experiments which showed that preying upon aquatic organisms, including malaria mosquito larvae, is not habitual for Pirata spp. (Araneae: Lycosidae) and Pardosa spp. spiders. These predators are terrestrial and find the bulk of their prey on land near the water's edge. The semi‐aquatic spiders of the genus Dolomedes are surface film locomotors and active predators of mosquito larvae as part of a broad diet (Zimmermann & Spence, 1989). When fed only Anopheles larvae, they grew normally and successfully completed development. Argyroneta aquatica is another active predator of anopheline mosquitoes. These predate underwater using a network of threads surrounding a bell‐shaped nest made of silk and submerged aquatic plants. The spider fills the nest with air and hides inside while trapping its prey (Perevozkin et al., 2004). The food preferences of Dolomedes and Argyroneta were found to depend on the size of their prey and its mode of locomotion. Argyroneta aquatica preferred hunting Anopheles larvae, irrespective of differences in body size between them and Culex larvae. Anopheles larvae move jerkily in water and these movements attracted the spider; Culex larvae glide more smoothly. Futami et al. (2008) also studied the predatory ability of wolf spiders alongside the predator avoidance techniques of An. gambiae. Diving ability develops with instar stages of An. gambiae (Tuno et al., 2007), which may affect predation by wolf spiders. Although predation intensity was low for first instars, separate experiments showed that spiders could capture nearly 50% of second, third and fourth instars within 24 h. General mortality increased with mosquito age, except for pupae. Fewer pupae were captured, possibly because they are less active; when they do move, they do so quickly and their smooth round shape makes them harder to grip. These results, along with all other laboratory tests, cannot be directly extrapolated to describe the predatory capacity of this spider in nature.

Flatworms (Planaria) Planarians are free‐living flatworms and form the traditional class Turbellaria in the phylum Platyhelminthes; other classes of flatworms are parasitic. A rhabdocoele turbellarian is identified as predatory on aquatic arthropods, including aquatic stages of An. gambiae s.l. One worm can kill an individual larva, but the individual attack is typically followed by a mass attack (Mead, 1978). Kar & Aditya (2003) demonstrated how larvae of mosquitoes can be consumed by a species of planarian, Dugesia bengalensis (Tricladida: Dugesiidae). A laboratory experiment showed that planarians prefer the second and third larval stages of mosquitoes (Anopheles and Culex) in which the exoskeleton is not yet fully hardened. No alternative prey were offered and hence the extent of consumption or preference for mosquito larvae in the wild is not known. The most important flatworm predators are species of Mesostoma (Typhloplanoida: Typhloplanidae) that occur in a wide range of habitats. Single prey experiments show that a number of Mesostoma species feed heavily on mosquito larvae, some chironomid larvae and some daphnids, but considerably less on copepods and ostracods. Prey preference experiments reflect the same trends (Blaustein & Dumont, 1990).

Frogs, toads and tadpoles (Amphibia, Anura) When frogs and toads consume mosquitoes, it is usually thought to be as adults. Tadpoles are often largely herbivorous, although some larger species do prey on mosquito larvae. That said, the majority of the published research is focused on tadpoles. The dietary niche breadth of larvivorous tadpoles includes other predators of mosquito larvae. Their consumption of mosquito larvae in the presence of alternate prey has not been properly elucidated (Kumar & Hwang, 2006). Detailed studies by Service (1973) found both adult frogs and tadpoles in experimental ponds, small pools and ditches, but only tadpoles were found to consume An. gambiae s.l. [Hyperolius sp. (Anura: Hyperoliidae) and Phrynobatrachus sp. (Anura: Phrynobatrachidae)]. Service (1977), in a similar study, found both frogs and tadpoles but again only the tadpole gut content tested positive for An. gambiae s.l. [Phrynobatrachus sp. and Ptychadena sp. (Anura: Ptychadenidae)]. It is possible that the larger size and more rapid digestion rate of adult frogs does not lend itself to this method of testing stomach contents. The Asian bullfrog tadpole Hoplobatrachus tigerinus (Anura: Dicroglossidae) has been shown to effectively prey on larvae of Aedes aegypti; under laboratory conditions consumption per tadpole per day amounted to 29.0 ± 2.0 first instar larvae (Murugan et al., 2015).

Fish (Osteichthyes) Fish predation of mosquito larvae has been recorded in many habitats, from experimental small plastic containers to complex natural ecosystems. Larvivorous fish have been demonstrated to be effective at reducing larval mosquito populations in many parts of the world, through direct predation, and inhibition of development and of oviposition. Predatory and non‐predatory effects of the mosquito fish Gambusia affinis (Cyprinodontiformes: Poeciliidae) and Carassius auratus (Cypriniformes: Cyprinidae) on both gravid An. gambiae s.s. and larval survivorship revealed direct and indirect effects on life history traits of An. gambiae s.s. The presence of a predator reduced the number of larvae, but also reduced their growth and developmental rate, and hindered oviposition in potential larval habitats (Chobu et al., 2015). Similar findings have been reported in other studies conducted in both laboratory and semi‐field settings (Munga et al., 2006; Kweka et al., 2011). Physiological stress induced by the presence of predators can reduce adult body size and consequently their mating, fecundity, oviposition and survivorship potential. The larvivorous fish Oreochromis spilurus (Cichliformes: Cichlidae) (a tilapia) was assessed as an agent of malaria vector control in northern Somalia. The mean reduction observed in the field was 52.8%. In laboratory studies, the fish consumed all available larvae, but this did not occur in the field, where other foods were available and habitats offer options for larval predator avoidance (Mohamed, 2003). Louca et al. (2009) conducted semi‐field and field trials to look at comparative abundances of Anopheles and Culex mosquitoes in relation to native fish populations. Another semi‐field trial tested the predatory capacity of fish on mosquito larvae and influence of fish chemical cues on oviposition. In this, both Tilapia guineensis (Perciformes: Cichlidae) and Epiplatys spilargyreius (Cyprinodontiformes: Aplocheilidae) were effective predators, removing all late‐stage culicine and anopheline larvae within 1 day. In the field, there was less chance of finding culicine larvae where T. guineensis was present; however, the presence of Anophelines was not related to the presence or absence of any fish species. These studies indicate that although T. guineensis is a predator of mosquito larvae, it is not a specialist (Kumar & Hwang, 2006; Louca et al., 2009). Kweka et al. (2011) found survival rates in semi‐field experiments varied with predator species, but not larval density and habitat type, reflecting the combined effects of searching and consumption of An. gambiae s.l. larvae by predator species in both time and space. Studies of the gut content of Gambusia holbrooki showed these fish to be true generalists and recorded 34% algae and 19% detritus, in addition to invertebrate prey. Animal consumption included 11% rotifers, 28% dipterans, 19% ostracods, 19% other insects, 18% copepods and 5% cladocerans (Garcia‐Berthou, 1999; Specziár, 2004). Hence, although potentially a contributor to biological control of mosquitoes, all fish, including the mosquito fish G. affinis, are flexible and generalist predators. Although mosquito larvae are often proposed as important in the natural diet of fish, exclusions of mosquitoes from aquatic habitats caused by predation, or avoidance by ovipositing female mosquitoes, have rarely been studied. In Colombia, larvae of Anopheles albimanus were negatively associated with fish and predatory invertebrates, such as dragonfly and mayfly nymphs. These fish maintain their niche occupation whether or not mosquito larvae are present (Marten et al., 1996).

Birds (Aves) Many of the birds that make use of freshwater habitats are insectivorous and are likely to feed on mosquito larvae as part of a broad opportunistic diet. There is little quantitative evidence of specific mosquito consumption in the aquatic larval habitat. Further information on predation by birds is given under the section on predation of adults.