Thermal behaviour and biological activity of pyrethroids in smoke-generating formulations

Smoke‐generating insecticide formulations are nowadays very important for the control of Chagas' disease vectors. In this work, the thermal decomposition of different pyrethroid insecticides in smoke‐generating formulations has been studied. Their recovery from the smoke has been determined, and the effect on this of the addition of foaming agents such as cyanoguanidine (CNG) or azodicarbonamide (ADC), or antioxidant agents such as butylated hydroxytoluene (BHT) or butylated hydroxyanisole (BHA) has been assessed. In each case the best smoke‐generating formulation was established. Calorimetric studies were done to justify the behaviour of the smoke‐generating mixtures. The isomerization process for different pyrethroids was also studied, to establish the influence of the foaming agents in inhibiting isomerization to less active pyrethroids. Smoke‐generating mixtures containing β‐cypermethrin and cis‐permethrin as insecticides and CNG or ADC as foaming agents were evaluated for their insecticidal activity against nymphs I of Triatoma infestans, vector of Chagas' disease. The best effect was found with β‐cypermethrin formulated with ADC, with LT50 values lower than 5 min. © 1999 Society of Chemical Industry