New Applications for Neonicotinoid Insecticides Using Imidacloprid as an Example

Abstract

Following the discovery of the insecticidal properties of the heterocyclic nitromethylenes (Soloway et al. 1979), chemists of Nihon Bayer Agrochem started in 1979 to optimize these structures. In 1985, the coupling of the chloropyridyl moiety to the N-nitro substituted imidazolidine ring system enabled the synthesis of the highly active insecticide imidacloprid (Kagabu 1999; Nauen et al. 2001; Jeschke et al. 2002). Imidacloprid is the first commercial example of the neonicotinoid (chloronicotinyl) insecticides acting agonistically on nicotinic acetylcholine receptors (Bai et al. 1991; Elbert et al. 1991; Nauen et al. 2001; Tomizawa and Casida 2003). The insect nicotinic acetylcholine receptor (nAChR) is one of the insecticidal targets which came into vogue after the introduction of the first neonicotinoid (chloronicotinyl) insecticide imidacloprid by Bayer CropScience in 1991, which was reviewed very recently (Nauen et al. 2001). Since the launch of imidacloprid (top-selling insecticide worldwide today), neonicotinoids have developed into a major class of insecticides with several other (commercialized) active ingredients having been described over the last decade and representing some 12% of the insecticide market in 1999 (Nauen and Bretschneider 2002), e.g., acetamiprid (Takahashi et al. 1992), nitenpyram (Minamida et al. 1993), thiamethoxam (Maienfisch and Sell 1992), dinotefuran (Kodaka et al. 1998), thiacloprid (Elbert et al. 2000), and clothianidin (Ohkawara et al. 2002). All neonicotinoid insecticides are effective against sucking insects such as aphids, whiteflies and planthoppers, but also beetles and some lepidopteran pests, such as leaf miners and Cydia pomonella (Elbert and Nauen 1998; Elbert et al. 2000). Although it has been on the market for more than a decade, imidacloprid has proved remarkably resilient to resistance, and only a few geographically localized cases of neonicotinoid resistance have been reported, e.g., Bemisia tabaci in southern Spain (Denholm et al. 2002; Nauen et al. 2002).