**4. Classification of propesticides**

Propesticides can be classified in two ways like based on the number of activation steps involved and based on the type of pest to control [11]. Based on the number of activation steps involved propesticides are classified as single step activation and multiple step activation.

#### **4.1. Single step activation**

#### *4.1.1. Juvenogens*

• The term juvenogen is used to indicate a new class of the complex chemical compounds which generate products with juvenile hormone activity in response to certain biotic or environmental factors.

• Juvenogen esters when topically applied, the wax-like ester enters the insect body where it is enzymatically hydrolyzed by the carboxylesterase enzymes.

*4.2.3. Flouromevalenate*

prorodenticides.

**5.1. Proinsecticides**

**5.2. Rodenticides precursors**

Zn3

These are potent inhibitors of juvenile hormone production in insects.

Accordingly propesticides are classified as proinsecticides, proherbicides, profungicides and

Propesticides and Their Implications http://dx.doi.org/10.5772/intechopen.71532 111

*N*-Methylcarbamates are another major group of insecticides inhibiting AChE.Although the proinsecticidal features of OP compounds were discovered after their development, proinsecticidal carbamates were designed in Fukuto's laboratory by systematic derivatization to *N*-phosphoryl, *N*-sulfenyl, and related carbamates [14–16]. The biological and toxicological properties of these carbamates could be tailored according to particular use requirements by changing the derivatizing moiety, and thus the physicochemical properties, such as lipophilicity (log P), of the resulting product. The propesticide is activated in the insect by chemical hydrolysis by thiols or other nucleophiles. Nereistoxin is a cyclic disulfide isolated from a marine annelid [17, 18]. It served as the lead compound for the development of the proinsecticides cartap and thiocyclam, both converted into dithiolane acting at the nicotinic acetylcholine receptor of insects. The precocenes, such as precocene 2, on the other hand, were isolated from *Ageratum* sp. plants and found to inhibit the terminal (oxidative) step of JH biosynthesis in the corpora allata, causing precocious development of the insect larva. These anti-juvenile hormones, also called proallatotoxins, are "suicide inhibitors" because the cytochrome P450 catalyzed oxidation of the chromene generates epoxide that reacts with neighboring nucleophiles of the enzyme protein, causing massive cellular damage. Diafenthiuron is a thiourea insecticide inhibiting mitochondrial ATPase and acts via its carbodiimide metabolite [19]. The phenylpyrazole fipronil contains a sulfoxide group that can undergo cytochrome P450-catalyzed oxidation in insects to yield a more potent sulfone metabolite. These are meant for controlling insect pest [20]. Some of the proinsecticides along

with their active metabolite and activation processes are given in the **Table 1**.

**Propesticides Active metabolite Activation process**

Scilliroside Scillirosidin Hydrolysis Bromethalin — *N*-Dimethylation

P<sup>2</sup> PH<sup>3</sup> Hydrolysis/acidolysis

Fluoroacetic acid and fluoroacetamide are "lethal precursors" to 2-fluorocitrate. Bitter scilliroside, from the red squill, can be hydrolyzed by glycosidases *in vivo* to scillirosidin, its

Flouroacetic acid or flouroacetamide Flourocitric acid Condensation with oxaloacetate/hydrolysis and

condensation with oxaloacetate

**5. Based on the type of pest to control**

• About two orders of magnitude faster hydrolysis of the juvenogen substrate has been found in the larvae of *Dysdercus*. Here juvenogen has much higher juvenile hormone activity than the hydrolysis alcohol product itself.

### *4.1.2. Procarbamates and proformamidines*

These are derivatives of toxic methyl carbamates insecticides which can be activated to active toxophore either by enzymatic or nonenzymatic. There are also other two possible mechanism of activation of these groups of compounds. These are:


#### *4.1.3. Photoactivated compounds*


#### **4.2. Multistep activation**

Propesticides requiring more than one metabolic process for activation are known as prepropestides. These are:

#### *4.2.1. Flourocitrate precursors*


#### *4.2.2. Cycloprate*

This is activated by two stage of activation process. First is hydrolysis of the cycloprate to free acid followed by formation of carnitine ester [12, 13]. Thus it inhibits the activity of carnitine in transport of fatty acids. Here, the carnitine is an amino acids commonly occurring in the liver and in skeletal muscles that function in the transport of fatty acids across mitochondrial membrane.

#### *4.2.3. Flouromevalenate*

• Juvenogen esters when topically applied, the wax-like ester enters the insect body where it

• About two orders of magnitude faster hydrolysis of the juvenogen substrate has been found in the larvae of *Dysdercus*. Here juvenogen has much higher juvenile hormone activ-

These are derivatives of toxic methyl carbamates insecticides which can be activated to active toxophore either by enzymatic or nonenzymatic. There are also other two possible mecha-

• Propheromones, xanthene dyes and natural photosensitizers are some types of compounds

• Xanthene dyes like erythrisin, fluorescin act as phototoxic agents against bacteria and

• Natural photosensitizers like terthienyl and polyacetylines, DNA-damaging agents like

Propesticides requiring more than one metabolic process for activation are known as prepro-

**ii.** One of the first poisons for which the biochemical mode of action was precisely described. **iii.** Nissol and Fluemethyl are two commercial product used as acaricides are of relatively

This is activated by two stage of activation process. First is hydrolysis of the cycloprate to free acid followed by formation of carnitine ester [12, 13]. Thus it inhibits the activity of carnitine in transport of fatty acids. Here, the carnitine is an amino acids commonly occurring in the liver and in skeletal muscles that function in the transport of fatty acids across mitochondrial

• Thiol induced thiolysis to form a mixed disulfide and toxic methyl carbamate.

dictamine, harmaline are some compounds which act as insecticides.

**i.** These occur as the toxic principle in legume genera.

is enzymatically hydrolyzed by the carboxylesterase enzymes.

ity than the hydrolysis alcohol product itself.

nism of activation of these groups of compounds. These are:

*4.1.2. Procarbamates and proformamidines*

110 Insecticides - Agriculture and Toxicology

• Acid catalyst hydrolysis of the N-S bond

those functions by photoactivation.

*4.1.3. Photoactivated compounds*

**4.2. Multistep activation**

*4.2.1. Flourocitrate precursors*

lower mammalian toxicity.

pestides. These are:

*4.2.2. Cycloprate*

membrane.

insects.

These are potent inhibitors of juvenile hormone production in insects.
