Colonies of honeybees are susceptible to a number of pesticides whose damage has negative economic impacts on the beekeeping industry and agriculture. This paper aims at revealing” DECIS 25EC”phytosanitary product toxicity. Experiments were carried out in an apiary of honeybees derived from Apis mellifera intermissa during May-December 2013. The insecticide acute toxicity was evaluated by topical and oral application to calculate lethal concentration. Results showed a considerable toxic effect on topical application comparing to the oral one. The LC50 and LC90 estimated at 24 hours by topical exposure on bees thorax were of 10.40ppm and 28.89ppm. At 96 hours, they were respectively 4.23ppm and 10.44ppm. Corrected mortality was considerable after (24 hours) oral exposure of the same treatment by the following concentrations of (4ppm; 10ppm; 25ppm; 50ppm; 100ppm; 200ppm), it varies between 10% and 93.33% with the concentrations of 4ppm and 200ppm respectively. A significant difference (p≤0.001) was noticed.