Inhibitors of chitin synthesis

Three series of compounds with this type of mode of action have been found, exemplified by polyoxin B, diflubenzuron, and buprofezin. Difluben-zuron belongs to the group called benzoylureas. 

The Pesticide Manual (Tomlin, 2000) describes 10 insecticidal benzoylureas. 

The two herbicides cichlobenil and diuron were built together in order to create a superherbicide but instead became the starting point for new insecticides 

Buprofezin is a specific poison for Homoptera, but the mode of action is not known. It is included in this chapter because it probably interferes with molting or chitin synthesis in some way It inhibits embryogenesis and progeny formation of some insects at very low concentrations (see Ishaaya, 1992). Cyromazil was first marketed in 1980 and is an insect growth regulator. Insect larvae, particularly fly larvae, develop cuticular lesions before they eventually die. 

Characteristically, their mammalian and fish toxicity are very low, and they have rather high acceptable daily intake (ADI) values. Tripathi et al. (2002) have made an extensive review on the chitin synthesis-inhibiting insecticides, including 156 references. 

In their search for new urea-type herbicides, the research workers of the Philips Duphar Co. established as an unexpected side-effect the insecticidal action of 

The preparation of this type of compound is illustrated by the synthesis of PH 60-38, in which 2,6-dichlorobenzamide (111), used also in the synthesis of the herbicide dichlobenil, reacts with p-chlorophenylisocyanate. 

Several processes are known for the preparation of 2,6-dichlorobenzamide(111). The most important process start from cyclohexanol and proceed according to the following reaction route (Anonym, 1967). 

Post et al. (1974) found disturbances in the endocuticular structure of insects treated with these derivatives. A characteristic symptom of the effect is the abortion of moult. These authors as well as Deul et al. (1978) concluded from their experiments involving the incorporation of labelled glucose in treated larvae, that 

Ishaaya and Casida (1974) investigated the insect cuticle chitin, as well as chitinase and phenoloxidase activity in housefly larvae treated with diflubenzuron, and observed a marked increase in activity of both enzymes. They concluded that 

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Summarizing, diflubenzuron features mentioned in the introduction of this paper can be completed as follows The new insecticide has favourable environmental properties because it is non-persistent in soils and it has a low biological magnification. It is stable on plants and in insects, hence it has a long residual activity. It represents the best choice from the series of the benzoylphenyl ureas. It is a reversible inhibitor of chitin synthesis in insects, probably by blocking chitin synthetase. 

For understandable reasons, Trouvelot lost his interest in entomology, but became a clever astronomist. Materials used to fight back gypsy moth include the chemical pesticide Dimilin , an inhibitor of chitin synthesis. The biological pesticides, Bacillus thuringiensis, or naturally occurring gypsy moth virus is also quite useful. 

Inhibitors of acetolactate synthase Inhibitors of chitin synthesis... 

Fig. 26.1.2. Structure of peptidyl nucleoside antibiotic inhibitors of chitin synthesis.

An early representative to the benzoylphenyl ureas includes difiubenzuron, discovered by Philips-Duphar B.V. as an inhibitor of chitin synthesis, and commercialized in 1977 for control of lepidopteran and coleopteran pests in fruit, cotton. 

Post LC, De Jong BJ, Vincent WR. l-(2,6-Disubstituted benzoyl)-3-phenylurea insecticides. Inhibitors of chitin synthesis. Pestic. Biochem. Physiol. 1974, 4(4), 473 83. 

El-Gazzar, L.M., R.S. Patterson, and P.G. Koehler. 1988. Activity of chitin synthesis inhibitors on the cat flea, Ctenocephalides felis Bouche. Jour. Agricul. Entomol. 5 117-120. 

The Future of Chitin Synthesis Inhibitors for Crop Protection... 

Demark JJ, Bennett GW. Ovicidal activity of chitin synthesis inhibitors when fed to adult German cockroaches (Dictyoptera Blattellidae). 

Rojas MG, Morales-Ramos JA. Bait matrix for delivery of chitin synthesis inhibitors to the formosan subterranean termite (Isoptera Rhinotermitidae). J. Econ. Entomol. 2001, 94, 506-510. 

Ho, C.M., T.R. Hsu, J.Y. Wu, and C.H. Wang. 1987. Effect of dimilin, a chitin synthesis inhibitor, on the growth and development of larvae of Aedes albopictus Skuse. Chinese Jour. Entomol. 7 131-141. 

Marx, J.L. 1977. Chitin synthesis inhibitors new class of insecticides. Science 197 1170-1172. 

Chitin Synthesis Inhibitors. These are insect growth regulators that prevent the formation of the insect chitinous exoskeleton and thus produce a critical biochemical lesion during hatching, ecdysis, or pupation (44). These complex biochemical and physiological processes are unique to arthropods therefore, the benzoyl phenyl ureas are highly specific insecticides (44). 

Insects exposed to diflubenzuron and related compounds are unable to form normal cuticle (skin) because their ability to synthesize it is lost. Thus, the cuticle becomes thin and brittle, and is unable to support the insect or to withstand molting, a process requiring the shedding of the old cuticle, as in metamorphosis. Diflubenzuron and other chitin synthesis inhibitors have extremely low mammalian toxicity and are used against termites. 

I. Hammann, W. Sirrenberg, Laboratory evaluation of SIR 8514, a new chitin synthesis inhibitor of the benzoylated urea class, Pflanzenschutz-Nachr. 33 (1) (1980) 1-34. 

Chitin synthesis inhibitor and so interferes with the formation of insect cuticle... 

Buprofezin / A, / S (Cyclic urea) ) N NC(CH,j)3 N 0 CH(CHj)2 Probable chitin synthesis and prostaglandin inhibitor. Hormone disturbing effect, leading to suppression of ecdysis... 

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