Certain essential oils of plants are widely used as fragrances and flavors in the perfume and food industries. They have long been used as insect repellents. Recent investigations in several countries have confirmed that some plant essential oils not only repel insects, but have contact and fumigant insecticidal actions against vectors and agricultural pests. As part of an effort aimed at the development of reduced-risk pesticides based on plant essential oils, toxicity and sub-lethal effects of ten essential oils have been investigated using the “Tiger mosquito” Aedes albopictus and “Coconut mite” Aceria guerreronis as test vector and agricultural pest species. In this paper the biological activities of essential oils and their toxicity against mosquito and mite has been studied.