**2. Worldwide use of insecticides**

After herbicides, insecticides are the most extensively used pesticides in agriculture [1]. The principal insecticide consumers by continent were America (44.9%), Asia (29%), Europe (16%), Africa (6.4), and Oceania (3.7%), with the United States being the country with the highest insecticide consumption worldwide (**Figure 1**) [2]. Recently collected data, dating from 1998 to 2014, indicates that chlorpyrifos was the third most used organophosphate pesticide in the United States, only for corn cultivation, with a total of 1,122kg/ha. In the same country, the most widely used carbamate was carbaryl with a total of 1,024 kg/ha; while imidacloprid was the most used neonicotinoid, with 0.057 kg/ha. During the same time period, chlorpyrifos, carbaryl, and imidacloprid were among the top 10 most widely used insecticides in the United States [3]. Currently, these same pesticides are used in agriculture and are included among the principal insecticides for each insecticide family aforementioned [4–6].

Furthermore, organophosphate insecticides account for roughly half of all insecticides used worldwide, and chlorpyrifos is one of the most widely used. This insecticide is approved for use on more than 50 food crops in both developed and

**Figure 1.** *Highest to lowest insecticide use by continent.*

*Neurotoxic Effects of Insecticides Chlorpyrifos, Carbaryl, Imidacloprid, in Different Animal… DOI: http://dx.doi.org/10.5772/intechopen.100527*

developing countries [7]. About 50 chemicals belong to the carbamate family, which are utilized as fungicides, herbicides, and nematicides in addition to having insecticidal properties. Carbaryl was the first carbamate to be commercialized, and it is now more widely used than all other carbamates combined [8]. Neonicotinoids, on the other hand, appear to be the most widely employed insecticides worldwide, according to the literature. In fact, imidacloprid is the world's second most widely used pesticide, after only the controversial herbicide glyphosate [9, 10]. Neonicotinoids have largely replaced carbamates and organophosphates because they are considered less toxic to humans and insects, and they appear to be less resistant to neonicotinoids compared to other conventional insecticide classes [11].

## **3. Of the molecule, its structure, and mechanism of action**

#### **3.1 Chlorpyrifos**

Organophosphates are compounds of organic nature that contain phosphorus. Chlorpyrifos (O, O-diethyl-O-3,5,6-trichloropyridin-2-yl phosphorothioate) is an organic thiophosphate of the chloropyridine class [12]. The latter is one of the most widely used organophosphate insecticides in agriculture, primarily used on corn, soy, fruit trees, walnut trees, brussels sprouts, blueberries, broccoli, and cauliflower, among others. This pesticide is also used on golf courses, on ornamental plants, for treating wood, and in homes to combat mosquitoes, cockroaches, and ants [13]. Chlorpyrifos act by irreversibly inhibiting the acetylcholinesterase enzyme activity, which causes acetylcholine accumulation in the synaptic cleft, causing overstimulation of postsynaptic receptors and the consequent signs of intoxication [14].

#### **3.2 Imidacloprid**

Imidacloprid [1-[(6-chloropyridin-3-yl) methyl] imidazolidin-2-ylidene] nitramide is a neonicotinoid of the chloropyridinyl class [15], which like the insecticides of the same family, acts as an agonist of nicotinic cholinergic receptors (nAChRs) of insects and mammals [16, 17]. IImidacloprid is used in agriculture for corn, cotton, soybean, potato, wheat, and some vegetable seeds, as well as for soil treatment and foliar application on crops like orange, potato, and cotton. It is also utilized in the treatment of decorative plants and residential areas, industrial vegetation and forestry management [18]. Additionally, it is used as veterinary medicine in presentations such as pipettes or collars for direct application on dogs and cats to prevent infestations by internal and external parasites [19].

#### **3.3 Carbaryl**

Carbaryl (1-naphthyl methylcarbamate) is a carbamate-based pesticide. It's a carbamate ester made up of 1-naphthol and methylcarbamic acid. On plants, this pesticide is insecticidal, acaricidal, and even growth retardant when used in plants. It is currently used to treat corn, soybean, cotton, nuts, fruit, and vegetable crops in agriculture [20]. It is mostly used on apple, nut, and soybean crops in the United States. However, it is found in more than 40 crops around the world, including asparagus, squash, and potatoes. Its non-agricultural uses include ornamental plants, lawns, grass, roads, and buildings [21]. Carbaryl acts by inhibiting acetylcholinesterase. Nevertheless, unlike organophosphates, carbamates do it reversibly [22].
