Date: 3/30/99

Time: 8:30

Type: Symposium

Number: 114

New chemistries: Modes of action

M. Treacy and *P. Rensner, American Cyanamid, Princeton, NJ 08540
Contact e-mail: treacym@pt.cyanamid.com

The increasing incidence of single- and multiple-resistance to organophosphates, carbamates and pyrethroids by populations of pestiferous insect and mite species, along with the continual aim to develop pest control agents which present even lower risks to human health, wildlife and environmental resources, has led to a virtual revolution in chemical discovery and design by the private sector over the last 15 years. This research effort has recently flourished with offerings of numerous commercial pesticides with distinct molecular structure and pharmacology. Emphasis given to nitrogen heterocyclic chemistry has culminated in commercial development of several insecticides and acaricides exhibiting diversity in both pharmacodynamics and pharmacokinetics. For example, the "neonicotinoids", which exert their physiological lesion by binding to neuronal post-synaptic acetylcholine receptors, include the chloronicotinyl-nitroimine, imidacloprid, -cyanoimine, acetamiprid, and -nitromethylene, nitenpyram, as well as the chlorothiazole-nitroimine, thiamethoxam, and the hydrofuran-nitroimine, MTI466. Novel bioenergetic insecticides/acaricides include the aryl-substituted pyrrole, chlorfenapyr (a prodrug uncoupler of oxidative phosphorylation), and the pyridazinone, pyridaben (inhibitor of electron transport at Complex I). Two other neurotoxins derived from nitrogen heterocyclic chemistry are the phenylpyrazole, fipronil, and the indeno-oxadiazine, indoxacarb, which bind to GABA-gated chloride and voltage-sensitive sodium channels, respectively. The pyridine-azomethine, pymetrozine, has been reported to impart insecticidal activity by disrupting normal interaction between the foregut and nervous system. In addition to the molecules described above, new insecticides and acaricides have also been isolated via fermentation of actinomycetes, notably the 16-membered macrolides, abamectin and emamectin, which interfere with normal operation of GABA- and glutamate-gated chloride channels, and the 12-membered macrolide, spinosad, which has been reported to induce its primary lesion at acetylcholine receptors different than those of the aformentioned "neonicotinoids". New insect growth regulators include the 20-hydroxyecdysone agonists within the diacylhydrazine chemical family, such as tebufenozide, halofenozide, methoxyfenozide and chromafenozide.

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