**2. The fundamentals of insecticides**

Insecticides are described as "chemicals used to control insects by killing them or preventing them from engaging in undesirable or destructive behaviors" by United States Environmental Protection Agency (EPA) [6]. Insecticides provide substantial benefits during agriculture by controlling or preventing pests that could harm to crops and food causing nutritional and economic losses. Additionally, pests could damage wooden constructions and reduce the beauty and attractiveness of landscapes. Furthermore, insects could carry various diseases such as malaria [7, 8]. Insecticides play a crucial role in producing safe and quality food at affordable prices, home and gardening as well as controlling pest-borne diseases for public health.

Insecticides can be classified in varying ways such as their chemical structure, natural or synthetic origin, application requirement or mode of action. The chemical structure is particularly important for toxicology, since insecticides could exert similar toxicological effects due to their common chemical properties. Considering the chemical structure, insecticides could be divided into five groups: (i) organochlorines, (ii) organophosphates, (iii) carbamates, (iv) pyrethrins/pyrethroids and (v) nicotine/neonicotinoids.

Organochlorines have chlorinated hydrocarbon structures with high lipophilicity and persistence in the environment. Most exert their effects by disrupting sodium/potassium imbalance and others affect γ-aminobutyric acid (GABA) receptors; eventually, they cause hyperexcitation in the nervous system. Organophosphates, as another major class of insecticides, are phosphoric acid esters that cause acetylcholine accumulation at neuromuscular junctions by irreversible acetylcholinesterase (AChE) inhibition [6, 9, 10]. The other AChE inhibitor insecticide group carbamates are carbamic acid derivatives and show their effects reversibly, unlike organophosphates [11]. Pyrethrins are isolated from the flowers of *Chrysanthemum cinerariaefolium*; and, pyrethroids are synthetic analogs of pyrethrins. Both keep open the sodium channels, cause hyperexcitation in peripheral and central nervous systems and ultimately lead to paralysis. Pyrethrins and pyrethroids have lower environmental bioaccumulation and mammalian toxicity [12, 13]. Nicotine and neonicotinoids, as a newer class of insecticides widely used all over the world, have selectively neurotoxic effects on nicotinic acetylcholine receptor (nAChRs) [14].

High levels of exposure to several insecticides due to lack of legislations, regulations and education with ignorant behaviors may cause serious consequences on the human health and environment. Many studies showed that the misuse or overuse of insecticides lead to harmful effects in various systems such as nervous, respiratory and reproductive. The rest of this chapter gives details of the effects of selected insecticides on the female and male reproductive systems.

**239**

**Figure 1.**

*Reproductive Toxicity of Insecticides*

axis are shown in **Figure 1**.

**3.1 Hormonal system disruption**

tion of metabolic pathways [15–17].

*DOI: http://dx.doi.org/10.5772/intechopen.92890*

**3. Toxicity of insecticides on reproductive system**

Toxic effects of insecticides on male and female reproductive system and HPG

Insecticides could be characterized as "endocrine disrupters" due to their adverse effects on reproductive hormone pathway [15]. The half-life of endocrine-

Pyrethroids, synthetic esters of pyrethrins, widely used worldwide are important endocrine-disrupting chemicals. In animal studies, contradictory results were obtained about the effects of pyrethroids on HPG axis. It has been shown that permethrin, fenvalerate and cypermethrin exposure decreased serum testosterone levels and increased follicle stimulating hormone (FSH) and luteinizing hormone (LH) levels. Lower levels of testosterone constitute negative feedback in HPG axis resulting in increased levels of FSH and LH. However, in another study, delthame-

Elbetieha et al. [19] demonstrated that cypermethrin exposure decreased the serum testosterone, FSH and LH levels in male rats. On the other hand, different studies reported that pyrethroids have no effects on hypothalamus functions and

thrin exposure caused increased levels of testosterone, FSH and LH [18].

*Schematic representation of insecticides on male and female reproductive system via HPG axis (32).*

disrupting insecticides changes from hours to months in the environment. Insecticides may have toxic effects on synthesis, secretion, transport, binding to target receptors, intracellular transmission and elimination processes of reproductive hormones. In addition, insecticides alter hormone-receptor binding via chancing receptor affinity or agonist/antagonist effects, since, they mimic hormones. Thus, many of insecticides have estrogenic, androgenic or anti-estrogenic and antiandrogenic effects. Furthermore, insecticides could bind several types of receptors such as membrane, nuclear, orphan and neurotransmitter receptors. Endocrinedisrupting insecticides also exert toxic effects via inducing cell death in reproductive system cells playing a role from hormone synthesis to germ cell axis. Different studies confirmed that insecticides irreversibly affect hypothalamic-pituitary axis due to their mimicking properties of hormones or undesired inhibition or activa*Animal Reproduction in Veterinary Medicine*

**2. The fundamentals of insecticides**

diseases for public health.

(v) nicotine/neonicotinoids.

receptor (nAChRs) [14].

nists [5].

disruption.

cycle failures, decreased pregnancy rates, altered germ cell quality, reduced sperm motility as well as structural damage of testes or ovaries [4]. Furthermore, insecticides have important impacts on HPG axis and that qualifies them as endocrine disrupters. Endocrine-disrupting insecticides alter hormone synthesis or impair hormonal metabolic pathway by acting as hormonal receptor agonist or antago-

This chapter describes the reproductive system toxicity of commonly used insecticides based on each male and female; furthermore, it focuses on endocrine

Insecticides are described as "chemicals used to control insects by killing them or preventing them from engaging in undesirable or destructive behaviors" by United States Environmental Protection Agency (EPA) [6]. Insecticides provide substantial benefits during agriculture by controlling or preventing pests that could harm to crops and food causing nutritional and economic losses.

Additionally, pests could damage wooden constructions and reduce the beauty and attractiveness of landscapes. Furthermore, insects could carry various diseases such as malaria [7, 8]. Insecticides play a crucial role in producing safe and quality food at affordable prices, home and gardening as well as controlling pest-borne

Insecticides can be classified in varying ways such as their chemical structure, natural or synthetic origin, application requirement or mode of action. The chemical structure is particularly important for toxicology, since insecticides could exert similar toxicological effects due to their common chemical properties. Considering the chemical structure, insecticides could be divided into five groups: (i) organochlorines, (ii) organophosphates, (iii) carbamates, (iv) pyrethrins/pyrethroids and

Organochlorines have chlorinated hydrocarbon structures with high lipophilicity and persistence in the environment. Most exert their effects by disrupting sodium/potassium imbalance and others affect γ-aminobutyric acid (GABA) receptors; eventually, they cause hyperexcitation in the nervous system. Organophosphates, as another major class of insecticides, are phosphoric acid esters that cause acetylcholine accumulation at neuromuscular junctions by irreversible acetylcholinesterase (AChE) inhibition [6, 9, 10]. The other AChE inhibitor insecticide group carbamates are carbamic acid derivatives and show their effects reversibly, unlike organophosphates [11]. Pyrethrins are isolated from the flowers of *Chrysanthemum cinerariaefolium*; and, pyrethroids are synthetic analogs of pyrethrins. Both keep open the sodium channels, cause hyperexcitation in peripheral and central nervous systems and ultimately lead to paralysis. Pyrethrins and pyrethroids have lower environmental bioaccumulation and mammalian toxicity [12, 13]. Nicotine and neonicotinoids, as a newer class of insecticides widely used all over the world, have selectively neurotoxic effects on nicotinic acetylcholine

High levels of exposure to several insecticides due to lack of legislations, regulations and education with ignorant behaviors may cause serious consequences on the human health and environment. Many studies showed that the misuse or overuse of insecticides lead to harmful effects in various systems such as nervous, respiratory and reproductive. The rest of this chapter gives details of the effects of selected

insecticides on the female and male reproductive systems.

**238**
