**3. Mosquito control**

The prevention and control of mosquito-borne diseases globally is conducted through a comprehensive and thorough method of pest management. Where programs are not intended to completely eliminate mosquito populations but rather are aimed to reduce their number and therefore minimize the risk of disease transmission. Methods used to mosquito control include the elimination of breeding sites and the control of mosquito larvae and adults. Larvicides, by applying chemical insecticides in the breeding sites, are the best strategy to kill larvae and pupae of mosquitoes in the water. Larvicides are present in several forms ranging from powder, tablets, or liquids and include methoprene, monomolecular surface films, larvicidal oils, chemical insecticides, neurotoxic insecticides, plant-derived products, and larvicidal bacteria [19]. Adulticides technique is usually less efficient for mosquito control. However, it is the only way to kill adult mosquitoes and is the last line of defense in reducing mosquito populations. Some of the adulticide used for mosquito control include products derived from microorganisms, plants or minerals, synthetic molecules, organophosphates, some natural pyrethrins, or synthetic pyrethroids [63].

#### **3.1. Chemical insecticides**

Since its discovery, chemical insecticides have represented the most widely method used to control mosquito-borne vectors. However, the effects of chemical insecticides on mosquito vector populations are usually transitory because vectors can rapidly develop resistance against them. On the other hand, the environmental problems caused by the excessive use of chemical insecticides are a matter of current concern because it is estimated that about 2.5 million tons of pesticides are used annually, generating worldwide damage amounting to \$100 billion annually [64]. Some of the disadvantages that generates when using only chemical products are (a) the selection of new insecticide resistance in pest populations; (b) the resur‐ gence of already treated populations; (c) the generation of waste, risks, and legal complications; (d) the destruction of beneficial species; and (e) the high costs in equipment, labor, and material. In addition, the highly toxic and nonbiodegradable properties of insecticides and waste generated in soil, water, food, and crops that affect public health are additional reasons to search new methods to help solve the problems caused by chemical insecticides [64]. Conse‐ quently, the concept of integrated control arises, a method in which pest and diseases control is performed using chemicals, useful organisms, and cultural practices.

The progress of science and the chemical industry in the nineteenth century, with the discovery of DDT, made possible the development and emergence of new conventional insecticides or so-called of synthesis [65]. The most used of these insecticides of synthesis are modulators of sodium channels (organochlorines, pyrethroids, and pyrethrins), acetylcholinesterase inhibi‐ tors (carbamates and organophosphates), and the chloride channel antagonists regulated by the gamma-aminobutyric acid or also known as GABA (organochlorine cyclodiene and phenylpyrazoles).

Using these conventional insecticides gave positive results against insects disease vectors at first. However, due to its massive use, insects soon began to develop resistance to them. Thus, an insecticide that initially was effective, just being useless in the long term. In response to this problem, new-generation insecticides also called biorational insecticides have been developed, whose research strategy is based on a good understanding of the physiological processes or mechanisms specific communication of insects, and in obtaining agents that are able to affect them. These products are divided into the following: those who are analogs of juvenile hormone and molting, inhibitors tissue formation, pheromones, insecticides that prevent hatching, and biological insecticides [66].

#### *3.1.1. Organophosphates and carbamates*

from powder, tablets, or liquids and include methoprene, monomolecular surface films, larvicidal oils, chemical insecticides, neurotoxic insecticides, plant-derived products, and larvicidal bacteria [19]. Adulticides technique is usually less efficient for mosquito control. However, it is the only way to kill adult mosquitoes and is the last line of defense in reducing mosquito populations. Some of the adulticide used for mosquito control include products derived from microorganisms, plants or minerals, synthetic molecules, organophosphates,

Since its discovery, chemical insecticides have represented the most widely method used to control mosquito-borne vectors. However, the effects of chemical insecticides on mosquito vector populations are usually transitory because vectors can rapidly develop resistance against them. On the other hand, the environmental problems caused by the excessive use of chemical insecticides are a matter of current concern because it is estimated that about 2.5 million tons of pesticides are used annually, generating worldwide damage amounting to \$100 billion annually [64]. Some of the disadvantages that generates when using only chemical products are (a) the selection of new insecticide resistance in pest populations; (b) the resur‐ gence of already treated populations; (c) the generation of waste, risks, and legal complications; (d) the destruction of beneficial species; and (e) the high costs in equipment, labor, and material. In addition, the highly toxic and nonbiodegradable properties of insecticides and waste generated in soil, water, food, and crops that affect public health are additional reasons to search new methods to help solve the problems caused by chemical insecticides [64]. Conse‐ quently, the concept of integrated control arises, a method in which pest and diseases control

The progress of science and the chemical industry in the nineteenth century, with the discovery of DDT, made possible the development and emergence of new conventional insecticides or so-called of synthesis [65]. The most used of these insecticides of synthesis are modulators of sodium channels (organochlorines, pyrethroids, and pyrethrins), acetylcholinesterase inhibi‐ tors (carbamates and organophosphates), and the chloride channel antagonists regulated by the gamma-aminobutyric acid or also known as GABA (organochlorine cyclodiene and

Using these conventional insecticides gave positive results against insects disease vectors at first. However, due to its massive use, insects soon began to develop resistance to them. Thus, an insecticide that initially was effective, just being useless in the long term. In response to this problem, new-generation insecticides also called biorational insecticides have been developed, whose research strategy is based on a good understanding of the physiological processes or mechanisms specific communication of insects, and in obtaining agents that are able to affect them. These products are divided into the following: those who are analogs of juvenile hormone and molting, inhibitors tissue formation, pheromones, insecticides that prevent

some natural pyrethrins, or synthetic pyrethroids [63].

is performed using chemicals, useful organisms, and cultural practices.

**3.1. Chemical insecticides**

120 Insecticides Resistance

phenylpyrazoles).

hatching, and biological insecticides [66].

Organophosphate insecticides are phosphoric acid derivatives, having activity against a wide spectrum of invertebrate. It interferes with the action of enzymes called cholinesterases that regulate the neurotransmitter acetylcholine, resulting in first instance to muscle cramps, paralysis, and eventually death [67]. Therefore, these insecticides have a toxic action that blocks an enzyme acetylcholinesterase of central and peripheral nervous system of insects, in synaptic junctions. The enzyme rapidly hydrolyzed acetylcholine, resulting in the repolarization of the membrane or the basal plate in neuromuscular connections, preparing for the arrival of a new impulse. By forming strong covalent bonds between insecticide and acetylcholinesterase, the enzyme is inhibited, causing the accumulation of acetylcholine in the synaptic junction and the interruption of normal transmission of nerve impulses [68].

However, due to the generation of resistance in vector insects to these chemical products, the use of many of these organophosphate and carbamates insecticides is no longer effective. Furthermore, because cholinesterases and neurotransmitters acetylcholine also form part of vertebrate nervous system, organophosphate pesticides are highly or moderately toxic to vertebrates [69]. In this regard, temephos are the only organophosphate pesticide that is still used to control mosquito larvae. Although temephos are not persistent in the environment being that last 7–10 days [70], it has been shown in many studies the adverse effects of temephos on a wide range of no target aquatic taxa [71]. Furthermore, carbamate pesticides, just like organophosphates, act by inhibiting the cholinesterase enzyme. Therefore, the symptoms experienced by insects per carbamate poisoning are similar to those experienced with orga‐ nophosphates. However, carbamate pesticides block acetylcholinesterase enzyme hydrolyz‐ ing acetylcholine in muscle by carbamylation, which is a reversible reaction [72]. Therefore, the recovery of carbamate poisoning in humans is faster than with organophosphate intoxi‐ cation since the acetylcholinesterase enzyme is able to break apart of the carbamate [73].

#### *3.1.2. Organochlorines, pyrethroids, and pyrethrins*

Organochlorine insecticides are chlorinated hydrocarbons, which are known to be effective to control mosquito populations. Its mode of action is by inhibiting GABA receptor in the nervous system through the interruption of nerve impulses due to the closure of chloride channels [72]. Therefore, when an organochlorine binds to a GABA receptor, the receptor is unable to close GABA chloride channel, which results in stimulation of the nervous system and similar symptoms to poisoning with carbamates or organophosphates [74]. However, with the Stockholm Convention on Persistent Organic Pollutants, which entered into force on May 17, 2004, the use of 12 chemicals including DDT, aldrin, dieldrin, heptachlor, mirex, chlordecone, and chlordane was prohibited because of its long average life and toxicity [75]. However, an extension clause allows countries where malaria is endemic to use DDT to control vectors that transmit the disease. Taking into account the negative effects that DDT has for the environ‐ ment, malaria programs without the use of insecticides have been developed with the assistance of the Pan American Health Organization [76].

On the other hand, pyrethroids and pyrethrins used to control mosquitoes break down faster in the sunlight as opposed to chemical or microbial breakdown. However, pyrethroids are considered axonic poisons, composed of more stable substances, or degrade slower in the presence of sunlight than pyrethrins and are generally effective against most of the insect pests of agriculture. Furthermore, pyrethroids can be combined with other active ingredients, such as piperonyl butoxide, to retard its degradation and prevents the insect's system from detoxifying the pyrethroid, making it more effective [72]. Delay that allows the chemical product persists longer in the environment, requiring smaller and less frequent doses to kill pests [77]. This type of insecticidal affects the central and peripheral nervous system of insects and have a rapid knock-down effect, by interfering with the sodium channels of nerve membrane causing the interruption of the transfer of ions and transmission of impulses between nerve cells [78]. Moreover, it stimulates nerve cells to produce repetitive discharges and eventually cause paralysis and death [79]. Furthermore, because pyrethroids act on the nervous system of insects through a different pathway from the organophosphate pesticides, they generally have low toxicity in mammals and birds; however, they are toxic to fish and tadpoles [80].

#### *3.1.3. Biorational insecticides*

Biorational insecticides are those that have relatively low toxicity to humans and have few environmental effects. Among which, methoprene is an insect growth regulator insecticide with a broad spectrum of action that interferes with the insect life cycle preventing maturity or reproductive stage [81]. Meanwhile, the juvenile hormone analogue is a biorational insecticide that causes deformations in larval stage, death in the pupal stage, and sterility effect in adults [82]. Spinosad is another biorational insecticide that comes from a *Saccharopolyspora spinosa* neurotoxin, made by a mixture of spinosyns A and D. Spinosad act on the postsynaptic nicotinic acetylcholine receptors and GABA receptors and has proven its usefulness in the dipterans control [83]. Pyriproxyfene is another new-generation insecticide that has been tested in adult and larval mosquitoes causing a reduction in the number of sperm, egg production, blood feeding, and mating activity [84].

#### **3.2. Plants and their derivates**

For centuries, nature has created several active substances that, when applied correctly, can control insect pests such as mosquito in an efficient manner. The use of plants by man with insecticide purposes dates back to early human history. Due to their environmental advan‐ tages, the use of insecticides of vegetable origin in pest management has been increasing [85]. Among plants with potential activity against mosquitoes, Nim or Neem (*Azadirachta indica*) causes stunted growth, loss of appetite, reduction of fertility, molting disorders, morphological defects, and behavioral changes [86]. Moreover, it has been demonstrated that raw or partially purified plant extracts are most effective for mosquito control in place of the purified com‐ pounds or extracts [87]. The snuff (*Nicotiana tabacum*) is used, thanks to its insecticide and insect repellent action, where nicotine acts on the nervous system of insects through breathing, ingestion, and contact [88]. Other plants from which oils are extracted are garlic (*Ocimum basilicum*) and cinnamon (*Cinnamomum osmophloeum*), which have been shown to have insecticidal properties against larvae and adults of *A. albopictus*, *Culex quinquefasciatus*, and *Armigeres subalbatus*.

#### **3.3. Biological agents**

considered axonic poisons, composed of more stable substances, or degrade slower in the presence of sunlight than pyrethrins and are generally effective against most of the insect pests of agriculture. Furthermore, pyrethroids can be combined with other active ingredients, such as piperonyl butoxide, to retard its degradation and prevents the insect's system from detoxifying the pyrethroid, making it more effective [72]. Delay that allows the chemical product persists longer in the environment, requiring smaller and less frequent doses to kill pests [77]. This type of insecticidal affects the central and peripheral nervous system of insects and have a rapid knock-down effect, by interfering with the sodium channels of nerve membrane causing the interruption of the transfer of ions and transmission of impulses between nerve cells [78]. Moreover, it stimulates nerve cells to produce repetitive discharges and eventually cause paralysis and death [79]. Furthermore, because pyrethroids act on the nervous system of insects through a different pathway from the organophosphate pesticides, they generally have low toxicity in mammals and birds; however, they are toxic to fish and

Biorational insecticides are those that have relatively low toxicity to humans and have few environmental effects. Among which, methoprene is an insect growth regulator insecticide with a broad spectrum of action that interferes with the insect life cycle preventing maturity or reproductive stage [81]. Meanwhile, the juvenile hormone analogue is a biorational insecticide that causes deformations in larval stage, death in the pupal stage, and sterility effect in adults [82]. Spinosad is another biorational insecticide that comes from a *Saccharopolyspora spinosa* neurotoxin, made by a mixture of spinosyns A and D. Spinosad act on the postsynaptic nicotinic acetylcholine receptors and GABA receptors and has proven its usefulness in the dipterans control [83]. Pyriproxyfene is another new-generation insecticide that has been tested in adult and larval mosquitoes causing a reduction in the number of sperm, egg

For centuries, nature has created several active substances that, when applied correctly, can control insect pests such as mosquito in an efficient manner. The use of plants by man with insecticide purposes dates back to early human history. Due to their environmental advan‐ tages, the use of insecticides of vegetable origin in pest management has been increasing [85]. Among plants with potential activity against mosquitoes, Nim or Neem (*Azadirachta indica*) causes stunted growth, loss of appetite, reduction of fertility, molting disorders, morphological defects, and behavioral changes [86]. Moreover, it has been demonstrated that raw or partially purified plant extracts are most effective for mosquito control in place of the purified com‐ pounds or extracts [87]. The snuff (*Nicotiana tabacum*) is used, thanks to its insecticide and insect repellent action, where nicotine acts on the nervous system of insects through breathing, ingestion, and contact [88]. Other plants from which oils are extracted are garlic (*Ocimum basilicum*) and cinnamon (*Cinnamomum osmophloeum*), which have been shown to have

tadpoles [80].

122 Insecticides Resistance

*3.1.3. Biorational insecticides*

**3.2. Plants and their derivates**

production, blood feeding, and mating activity [84].

Among biological agents used for mosquito control can be mentioned derivatives of viruses, bacteria, and fungi. Entomopathogenic virus spreads from one insect generation to the next causing paralysis and eventually death on mosquito larvae being more effective in the first stage of development [89]. Within bacteria, only reports of *Bacillus thuringiensis*, *B. sphericu*s, and *B. popilliae* with possibilities to exercise control over dipterans insects currently exist. These bacteria, during the sporulation process, produce protein crystals with insecticidal effect and/ or some toxins with the same effect [90]. *Bacillus* initially causes diarrhea and intestinal paralysis in mosquito, giving rise to a decrease of body movements, convulsions, and general paralysis. Internally, within the mosquito stomach, *B. thuringiensis* releases toxic crystals that paralyze the insect gut stopping peristalsis, causing that the insect stop feeding and die by starvation. Within the gut, bacteria multiply until they break the epithelium and invade the rest of the insect body. However, its use for mosquito control is scarce and presents some drawbacks as its duration in the environment is limited, its dispersion is rather inefficient, and the susceptibility to bacterial infection in the pest population is very heterogeneous. There are very sensitive individuals and other highly resistant. Fungi are other microorganisms that may be used to control mosquito vectors, of which 400 species are known with insecticide potential. About 20 of them have been given more attention, including those in the *Lagenidium*, *Entomo‐ phaga*, *Neozygites*, *Entomophtora*, *Erynia*, *Aschersonia*, *Verticillium*, *Nomuraea*, *Hirsutella*, *Meta‐ rhizium*, *Beauveria*, and *Paecilomyces* genera [91]. Although, entomopathogenic fungi are not as specific as bacteria or viruses, spores persist and infect insect successive generations, so that when the infection is established, its effects can last several years. Infection occurs by adhesion of the spores on the insect cuticle, where these germinate and penetrate the cuticle leading to insect colonization by mycelium. Cuticle penetration occurs through the use of an enzyme complex that the fungi use to feed. The entomopathogenic fungus most used in controlling mosquito infestations is *Beauveria bassiana*, which produces various active ingredients such as beauvericin [92].

The biological control of mosquito larvae with predators and other biological control agents could be a more effective and environmentally friendly strategy, thus avoiding the use of synthetic chemicals and the consequent environmental damage [93]. Among them, some insects and vertebrates such as fish, amphibians, and some mammals have the potential to control mosquito disease–vector populations. Within vertebrates, amphibians, bats, and fish have been used to control populations of mosquito. For example, using larvivorous fish species, control of mosquito larvae in deposits used to store water has been achieved [41]. Moreover, bats are responsible for capturing flying insects such as mosquitoes at night; similarly, toads and frogs consume large numbers of insects, slugs, worms, and other inver‐ tebrates [94]. However, the use of frogs and tadpoles for disease vector control is still largely unexplored.
