Effect of UV-light, temperature, indoor dark and day light 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 temperature degrees and day light and dark storage after exposure intervals. The results indicated that rates of degradation of the five tested insecticides are varied according to the chemical structure, time of exposure and wavelength of UV-rays used. Methomyl was the most affected by UV-rays among of the five insecticides. Loss rate 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-rays exposure. Significant increase of LC₅₀ value was obtained when ES-Fenvalerate in aqueous preparation was exposed to UV-light for 6 hr. LC₅₀ values and their confidence ranges in aqueous preparations and emulsifiable concentrates were 107.5 ppm (51.7–199.2) and 93.10ppm (48.3–150.4). The residual level of ES-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, respectively . Insecticides could be arranged according 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, respectively. On the other hand the dark storage exposure for the tested insecticides could be arranged according 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 one day at 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 amount recovered after three days at 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 immature stages of whitefly insect, B. tabaci 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 and methomyl, were more affected by UV-light, storage and temperature than ES-Fenvalerate, pirimicarb and imidacloprid.