Review on Current Analytical Methods with Chromatographic and Nonchromatographic Techniques for New Generation Insecticide Neonicotinoids

Neonicotinoid insecticides are a major group and the newest group among insecticides. They permeate the entire body of a plant and show excellent effects for the control of diseases and harmful insects. The history of neonicotinoid insecticides from development to their market release dates back to the late 1800s. Nicotine (Fig. 1), an alkaloid in tobacco leaves, is an early neonicotinoid insecticide that has been used as a natural insecticide, but it is extremely toxic to mammals (LD50 = 50–60 mg/kg; Tomizawa & Casida, 2005). Therefore, studies using nicotine as a model compound have been conducted actively to develop new pesticides with highly selective toxicity. In the 1970s, Shell developed nithiazine (Fig. 1), which showed strong insecticide activity (Soloway et al., 1978, 1979), although the compound was unstable in its application and remained commercially unavailable. Subsequently, the development of nithiazine derivatives was continued based on the relation between the chemical structure of nicotine compounds and insecticide activity. Eventually, Nihon Tokushu Noyaku Seizo (currently Bayer Crop Science) developed imidacloprid (Fig. 1) (Shiokawa et al., 1994). Subsequent to imidacloprid, acetamiprid (Nippon Soda Co. Ltd.), nitenpyram (Takeda Chemical Industries, currently Sumitomo Chemical Takeda Agro Co.), thiamethoxam (Ciba, currently Syngenta), thiacloprid (Bayer Crop Science), dinotefuran (Mitsui Chemicals Inc.) and clothianidin (Takeda Chemical Industries, currently Sumitomo Chemical Takeda Agro Co.) have been released on the market (Tomlin, 2003) with the subsequent new and recent development of imidaclothiz in China (Nantong Jiangshan Agrochemical and Chemical Co. Ltd.) (Fig. 1). Neonicotinoid insecticides express insecticide activity by acting on the nicotinic acetylcholine receptor, nAChR, which is present on the postsynaptic membrane of the insect nerve. Excellent insecticide effects are expressed on hemipteran pest species including aphids, whitefly, and planthoppers by this mechanism of action. Although nAChR is present in both insects and mammals, neonicotinoid insecticides that act on them are highly selectively toxic to insects because the recognition site of insect nAChR is lipid-soluble, whereas mammalian nAChR must be ionized to a high degree. It is considered that the