Imidacloprid neonicotinoids

Imidacloprid is a widely used neonicotinoid insecticide that kills pests by targeting their central nAChRs. Levamisol is used to kill nematodes by acting on nAChRs in the worm s muscles. 

At a more subtle level, behavioral disturbances may make it more difficult for animals to find food. Pyrethroids, carbamates, OPs, and neonicotinoids can disturb the foraging activity of bees (Thompson 2003). Interestingly, effects have been shown upon the wagtail dance of bees, and this disrupts communication between individuals as to the location of nectar-bearing plants. Also, the neonicotinoid imidacloprid has been shown to adversely affect conditioned responses such as proboscis extension of honeybees (Guez et al. 2001). Nicotinoids can disturb the functioning of cholinergic synapses, which are involved in the operation of the proboscis reflex as... 

Neonicotinoids are potent broad-spectrum insecticides that exhibit contact, stomach and systemic activity. Acetamiprid, imidacloprid, nitenpyram, thiamethoxam and thiacloprid are representatives of the neonicotinoid insecticides (Figure 1). The mechanism of action is similar to that of nicotine, acting on the central nervous system causing irreversible blocking of postsynaptic nicotinic acetylcholine receptors (nAChR). Neonicotinoid insecticides are often categorized as antagonists of the... 

In general, neonicotinoids (except for nitenpyram) are metabolized slowly in plants, and remain mainly as the parent compounds. The definition of crop residues is for the acetamiprid and imidacloprid parent molecule. The definition of crop... 

HPLC determination can be carried out for most of the neonicotinoids. The average recoveries of imidacloprid in the various crops by the HPLC/PDA method were 88-94% at a fortification level of 0.25 mg and 96-99% at a fortification level of 0.05 mg kg . The overall average recovery for 30 samples was 95% with an RSD of 4.7%.12... 

The polar character of neonicotinoids makes them, in general, potentially mobile in soil. Acetamiprid and nitenpyram have short soil persistence. Imidacloprid and thi-amethoxam, however, are sufficiently persistent in soil to be used for soil treatment. The definition of soil residues for the various neonicotinoid compounds except for imidacloprid are the parent compound and it metabolites. The metabolites of acetamiprid are lM-1-2, lM-1-4 and lC-0 (Figure 6). The metabolites of nitenpyram are 2-[N-(6-chloro-3-pyridyl-methyl)-A-ethyl]amino-2-methyliminoacetic acid (CPMA) and A-(6-chloro-3-pyridylmethyl)-Ai-ethyl-A -methylformamidine] (CPMF). 

The tobacco compound nicotine has been used as an insecticide for over 200 years. It is especially effective against sucking insects, such as aphids, and has excellent contact activity. Related compounds are neonicotinoids (e.g., imidacloprid), which have similar insecticidal activity, but are less toxic to mammals. Nicotine and imidacloprid mimic the action of acetylcholine, which is the major excitatory neurotransmitter in an insect s central nervous system. The action of acetylcholine is stopped by the enzyme acetylcholinesterase, which rapidly breaks down acetylcholine. Nicotine and imidacloprid are also neuroexcitatory, but do so persistendy, since they are not affected by acetylcholinesterase. Overstimulation of the nervous system often leads to convulsions, paralysis, and death. 

Imidacloprid will be used to illustrate the fate of neonicotinoid insecticides (Figure 8.32). Imidacloprid is reduced (1) and then becomes the triazine derivative (2). It can be hydroxv-lated at the imidazole ring to become themonohydroxylated derivatives (3 and 4). Reduction of parent imidacloprid to the nitroso derivative (5) occurs in some animal species. Imidacloprid is also cleaved to become the nitroiminoimidazololidine (6). Further metabolism involves olefin formation (7), glycine conjugation (8), and others. 

In a recent study, resistance to the neonicotinoid insecticide, imidacloprid, in the brown plant hopper, Nilaparvata lugens, was found to be due to a point mutation at a conserved position in two nAChR subunits. As a result, it reduced the receptor binding of imidacloprid (Liu et al., 2005). 

Most soils have a pH ranging from 4 to 9. The degradation of pesticides such as organo-phosphates and carbamates is affected by the pH of the soil. Most organophosphates are hydrolyzed under alkaline conditions, but diazinon is unstable in acid soils. Carbamates such as carbofuran are also hydrolyzed under alkaline conditions. The persistence of neonicotinoids is primarily determined by the pH. Imidacloprid and thiamethoxam are hydrolyzed under alkaline conditions, whereas thiacloprid and acetamiprid are less stable... 

H]neonicotinoid (35) [38,39]. Along with the azido a diazirinyl group is another prevailing photogenerator [40]. Matsuda et al. designed W-[ff -(trifluoromethyl)diazirinyl benzyl]imidacloprid as a photoaffinity probe [41],... 

Imidacloprid or l-[(6-chloro-3-pyridyl methyl]-N-nitro-2-imidazol idinimine Neonicotinoid Systemic uptake by plant and further distributed through the leaves, acts through central nervous system of insects Control of sucking insects, termites, biting insects 11-16... 

Imidacloprid is a neonicotinoid insecticide that is registered for many uses, including grub and termite control, crop protection, and to control fleas and ticks on companion animals. Its insecticidal activity is attributed to nicotinic activity on post-synaptic receptors. 

The acute toxicity (i.e., lethal potency) of imidacloprid, other neonicotinoids, and related analogs in mammals is most closely related to potency at the 7 nicotinic receptor subtype, followed in order by potency at 1x4, fSx, 0(3, and aj nicotinic receptors, respectively. However, acute toxicity in mammals involves complex actions (agonist and antagonist) at multiple receptor subtypes and these actions vary greatly with minor changes in chemical structure. 

Nithiazine was the lead compound in syntheses of the first commercially successful neonicotinoids that surpassed the parent compound in both insecticidal properties and environmental stability. A 6-chloro-3-methylpyridine moiety and a pharmacophore of varying structures (Figure 2) are the two components of a neonicotinoid molecule. Insecticides of the first generation of neonicotinoids are best represented by imidacloprid (Nihon Bayer Agrochem, Japan) (Figure 2) and are also called chloronicotinyls or chloropyridyls. 

The toxicokinetics of the thianicotinyl thiamethoxam is similar to that of imidacloprid. When applied orally to rats, goats, or chickens, thiamethoxam is rapidly and almost quantitatively absorbed. Its excretion, predominantly in urine, is fast. Accumulation in tissues is negligible. Thiamethoxam itself does not bind strongly to the neonicotinoid binding site of the nicotinic acetylcholine receptor but it is reported to be converted to clothianidin, a neonicotinoid with high affinity for the insect receptors, in insects and plants (Figure 6). It is possible that this activation proceeds via formation of an N-desmethyl thiamethoxam intermediate, another... 

The neonicotinoids were mainly developed in Japan, but imidacloprid is sold by the German company Bayer AG. 

Recently, resistance to imidacloprid became a serious problem for crop protection. Comparative studies of other neonicotinoids revealed a high crossresistance to acetamiprid and thiamethoxam against imidacloprid-resistant strains [22]. However, bioassays exhibited that 4a has good activity against imidacloprid-resistant strains of brown planthopper (Table IV), showing very low cross-resistance to imidacloprid, as shown in Table V. 

The lead compound, which initiated interest in the neonicotinoids, is a nitro-methylene heterocycle, nithiazine (Figure 1) [1]. Nifhiazine, with its unique nitromethylene moiety, showed low mammalian toxicity, but its insecticidal potency and field stability were inferior to commercial organophosphates and pyrethroids. Thus, nithiazine was not of commercial use for pest control. However, the introduction of 6-choloronicotinyl and 2-nitroimino-imidazolidine moieties led to the development of the first commercial neonicotinoid imidacloprid (Figure 1)... 

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