N-(PYRID-3-YL)THIOUREAS AND DERIVATIVES AS ACARICIDES .2. QUANTITATIVE STRUCTURE-ACTIVITY-RELATIONSHIPS AND CHEMODYNAMIC BEHAVIOR

The biological activity of a series of N-(pyrid-3-yl)thioureas and -ca rbodiimides, analogues of the insecticide/acaricide diafenthiuron, tow ards the carmine spider mite (Tetranychus cinnabarinus Boisd.) and the two-spotted spider mite (T. urticae Koch) was analysed using QSAR met hodology. A canonical correlation analysis allowed for the establishme nt of a prediction model and the identification of outliers within tha t model. The chemodynamic behaviour of certain compounds in the two se ries, including these outliers, determined by using photochemical expe riments in the laboratory as well as in the glasshouse, was shown to b e responsible for anomalous results obtained in the biological tests. It was found from the above study that the biological activity towards both spider mite species is extremely sensitive to the kinetics of fo rmation of the carbodiimides from the corresponding thioureas and to t he photostability of the former. The results obtained with a thiourea which underwent no appreciable photochemical transformation into the c orresponding carbodiimide supported the hypothesis that the thioureas are also in-vivo propesticides of the acaricidal carbodiimides.