Thiamethoxam is the first commercial neonicotinoid insecticide from the thianicotinyl subclass. It was discovered in the course of our optimisation program on neonicotinoids started in 1985. Novel variations of the nitroimino-heterocycle of imidacloprid led to 4-nitroimino-1,3,5-oxadiazinanes exhibiting high insecticidal activity. Among these, thiamethoxam (CGA 293433) was identified as the best compound and selected for worldwide development. The compound can be synthesised in only a few steps and high yield from easily accessible starting materials. Thiamethoxam acts by binding to nicotinic acetylcholine receptors. It exhibits exceptional systemic characteristics and provides excellent control of a broad range of commercially important pests, such as aphids, jassids, whiteflies, thrips, rice hoppers, Colorado potato beetle, flea beetles and wireworms, as well as some lepidopteran species. In addition, a strong preventative effect on some virus transmissions has been demonstrated. Thiamethoxam is developed both for foliar/soil applications and as a seed treatment for use in most agricultural crops all over the world. Low use rates, flexible application methods, excellent efficacy, long-lasting residual activity and favourable safety profile make this new insecticide well-suited for modern integrated pest management programmes in many cropping systems.
Biocontrol pseudomonads are most known to protect plants from fungal diseases and to increase plant yield, while intriguing aspects on insecticidal activity have been discovered only recently. Here, we demonstrate that Fit toxin producing pseudomonads, in contrast to a naturally Fit-deficient strain, exhibit potent oral activity against larvae of Spodoptera littoralis, Heliothis virescens and Plutella xylostella, all major insect pests of agricultural crops. Spraying plant leaves with suspensions containing only 1000 Pseudomonas cells per ml was sufficient to kill 70-80% of Spodoptera and Heliothis larvae. Monitoring survival kinetics and bacterial titres in parallel, we demonstrate that Pseudomonas fluorescens CHA0 and Pseudomonas chlororaphis PCL1391, two bacteria harbouring the Fit gene cluster colonize and kill insects via oral infection. Using Fit mutants of CHA0 and PCL1391, we show that production of the Fit toxin contributes substantially to oral insecticidal activity. Furthermore, the global regulator GacA is required for full insecticidal activity. Our findings demonstrate the lethal oral activity of two root-colonizing pseudomonads so far known as potent antagonists of fungal plant pathogens. This adds insecticidal activity to the existing biocontrol repertoire of these bacteria and opens new perspectives for applications in crop pest control and in research on their ecological behaviour.
Neonicotinoids represent a novel and distinct chemical class of insecticides with remarkable chemical and biological properties. In 1985, a research programme was started in this field, in which novel nitroimino heterocycles were designed, prepared and assayed for insecticidal activity. The methodology for the synthesis of 2-nitroimino-hexahydro-1,3,5-triazines, 4-nitroimino-1,3,5-oxadiazinanes and 4-nitroimino-1,3,5-thiadiazinanes is outlined. Bioassays demonstrated that 3-(6-chloropyridin-3-ylmethyl)-4-nitroimino-1,3,5-oxadiazinane exhibited better insecticidal activity than the corresponding 2-nitroimino-hexahydro-1,3,5-triazine and 4-nitroimino-1,3,5-thiadiazinane. In most tests, this compound was equally or only slightly less active than imidacloprid. A series of structural modifications on this lead structure revealed that replacement of the 6-chloro-3-pyridyl group by a 2-chloro-5-thiazolyl moiety resulted in a strong increase of activity against chewing insects, whereas the introduction of a methyl group as pharmacophore substituent increased activity against sucking pests. The combination of these two favourable modifications led to thiamethoxam (CGA 293 343). Thiamethoxam is the first commercially available second-generation neonicotinoid and belongs to the thianicotinyl sub-class. It is marketed under the trademarks Actara for foliar and soil treatment and Cruiser for seed treatment. The compound has broad-spectrum insecticidal activity and offers excellent control of a wide variety of commercially important pests in many crops. Low use rates, flexible application methods, excellent efficacy and the favourable safety profile make this new insecticide well-suited for modern integrated pest management programmes in many cropping systems.
tolerance9 and herbicide resistance8 to a variety of other herbicides.In conclusion, puriücation of a GST from susceptible black-grass revealed one polypeptide, whilst puriücation from a resistant black-grass biotype, which had approximately double the GST activity of susceptible biotypes, resulted in two polypeptides. The additional polypeptide had a slightly higher molecular mass and, although GST activity cannot be attributed to this polypeptide, it was eluted from a GSH affinity column with a peak of GST activity. A study of crude enzyme extracts of black-grass revealed that both atrazine and CTU can aþect the enzymic conjugation of GSH with the artiücial GST substrate CDNB. These observations will allow further study of herbicides' interaction with GST activity, and the role of GSTs in herbicide resistance. ACKNOWLEDGEMENTSWe thank the Home Grown Ceareals Authority, UK for funding. REFERENCES
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