Selective toxicity of acetamiprid (Mospilan 20% SP) and imidacloprid (Imaxi 35% SC) neonicotinoid insecticides to Bemisia tabaci, Spodoptera littoralis and Apis mellifera was studied. Assessment of  biochemical alterations total proteins, acetylcholinesterase EC3.1.1.7(AChE) activity, cytochrome P450 monooxygenases EC1.14.14.1 (CP450)  activity and glutathione-S-transferases EC2.5.1.18 (GST) activity were recorded and discussed as biomarkers for acetamiprid and imidacloprid selective toxicity in the exposed insects .  Imidacloprid treatments caused higher reductions in the total protein levels as compared with acetamiprid treatments. The total protein were decreased by 55, 41, 31 and 14 % in A. mellifera thorax, S. littoralis 2^nd larval instar, B. tabaci adult and S. littoralis 4^th larval instar, respectively. AChE activity was increased by 29% and decreased by 50% in A. mellifera whole body in acetamiprid and imidacloprid treatments, respectively. Moreover in B. tabaci, the enzyme activity was decreased by 9% and increased by 35% respectively after acetamiprid and imidacloprid treatments. The two tested neonicotinoids elevated CP₄₅₀ activity in B. tabaci adults and S. littoralis 2^nd and 4^th laraval instars. The highest increase was obtained with imidacloprid treatment in A. mellifera thorax (165%) followed by S. littoralis 2^nd larval instar (100%), B. tabaci adults (66%). The obtained results showed that acetamiprid and imidacloprid treatments elevated GST activity respectively by 29 and 1.5 % in B. tabaci adults; 30 and 30% in S. littoralis 4^th laraval instar  ;88 and 59% in  A. mellifera  thorax  . GST activity was decreased by 18% in S. littoralis 2^nd larval exposed to acetamiprid and increased by 18% in imidacloprid treatment. Conclusively, our work suggested that the selective toxicity of the cyanoguanidine neonicotinoid acetamiprid and the nitroguanidine neonicotinoid  imidacloprid was based on their chemical structure and metabolic pathways and seemed  to be represent  a species-specific feature .This was indicated by alterations of the values of total proteins and enzymes specific activity of key enzymes in the exposed target and non target insects .