A study was conducted to determine the activity and mechanism of action of three essential oils [eugenol, -terpineol and cinnamic alcohol] and an equal part mixture [3-blend] against American cockroaches [Periplaneta americana]. To address species differences in response to treatment with the test oils, Carpenter ants [Camponotus pennsylvanicus De Geer], and German cockroaches [Blattella germanica] were included in this study. Exposed American cockroaches demonstrated hyperactivity followed by hyperextension of the legs and abdomen, then fast knockdown or quick immobilization followed by death. Ants and German cockroaches showed fast immobilization/knockdown followed by mortality. The 1:1:1mixture [3-blend] was more efficacious against all test insects. One of the most remarkable observations was the increased frequency of heart beats of American cockroaches in response to topical application of test oils. The changes in the pattern of cAMP [cyclic Adenosine Monophsphate] level were biphasic. A significant increase in the CAMP level was found in response to 1 nmole/ml of eugenol, or 3-blend or 10 nmole/ml of a-terpineol. At higher concentrations a significant decrease in cAMP level was found. In conclusion: 1- Test oils are neuro-insecticides and their insecticidal activity is species-dependent. 2- A synergistic effect of the three oils was found when they were equally mixed [3-blend], and 3- CAMP-signaling pathway mediates the insecticidal activity of eugenol, a-terpienol and the 3-blend.