Effects of Uv-light, Temperature and Storage on the Stability and Biological Effectiveness of Some Insecticides

The degradation and biological effectiveness of five insecticides, ES-Fenvalerate (Soumi Gold), pirimicarb (Afox), imidacloprid (Emax), buprofenzin (Ablloud) and methomyl (Methiolate) in their aqueous preparations and emulsifiable concentrates, on immature stages of whitefly insect Bemisia tabaci. when exposed to UV-light, two different temperatures and daylight and dark storage after exposure intervals was studied. The results indicated the degradation rates of the five tested insecticides varied according to the chemical structure, time of exposure and wavelength of UV-rays used. Of all the five insecticides, methomyl was the most affected by UV-rays. Losses of ES-Fenvalerate, pirimicarb, imidacloprid, buprofenzin and methomyl within this period were 11.30, 14.80, 29.03, 31.83 and 39 %, respectively after one hour to UV-ray exposure. A significant increase in LC50 value was obtained when ES-Fenvalerate in aqueous preparation was exposed to UV-light for 6 hr. The LC50 values and their confidence ranges in aqueous preparations and emulsifiable concentrates were 107.5 ppm (51.7–199.2) and 93.10 ppm (48.3–150.4). The residual level of Fenvalerate, pirimicarb, imidacloprid, buprofenzin and methomyl were 13.52, 17.54 ppm; 12.67, 15.87 ppm; 11.78, 16.47 ppm; 11.38, 14.73 ppm; and 11.36, 11.83 ppm for two days exposed to daylight and dark storage. Insecticides could be arranged according to LC50 values at zero-time as follow: ES-Fenvalerate, pirimicarb, imidacloprid, buprofenzin and methomyl. The corresponding values of LC50 were 3.40, 15.4, 15.6, 16.2 and 23.5 ppm for daylight storage. On the other hand, the dark storage exposure for the tested insecticides could be arranged according to LC50 values as follow: ES-Fenvalerate, imidacloprid, pirimicarb, buprofenzin and methomyl. The corresponding LC50 were 3.20, 14.8, 14.9, 15.9 and 21.3 ppm, respectively. In general, the amount recovered after a one day, 45°C exposure were 14.63, 12.84, 12.79, 12.14 and 11.76 ppm, for ES-Fenvalerate, pirimicarb, imidacloprid, buprofenzin and methomyl, respectively. While the amounts recovered after a three day 45°C exposure were 9.28, 8.34, 7.76, 7.72 and 5.83 ppm for ES-Fenvalerate, pirimicarb, imidacloprid, buprofenzin and methomyl, respectively. Efficiency against whitefly insect, B. tabaci immature stages was affected when aqueous preparations of the five tested insecticides were stored at 45°C for one and three days, compared to those stored under normal condition of 25°C for the same periods of time. Generally it could be concluded that buprofenzin n and methomyl, were more affected by UV-light, storage and temperature than ES-Fenvalerate, pirimicarb, imidacloprid.