Comparative toxicity of essential oils of Litsea pungens and Litsea cubeba and blends of their major constituents against the cabbage looper, Trichoplusia ni.

Contact toxicity of essential oils of Litsea pungens Hemsl. and L. cubeba (Lour.) Pers. (Lauraceae) and of blends of their major constituents was assessed against third-instar Trichoplusia ni larvae via topical application. Both oils showed moderate activity against T. ni larvae with LD(50) values of 87.1 and 112.5 microg/larva, respectively. 1,8-Cineole from the essential oil of L. pungens and gamma-terpinene from the oil of L. cubeba accounted for much of the toxicity of the oils to T. ni larvae. The toxicity of blends of selected constituents indicated a synergistic effect among putatively active and inactive constituents, with the presence of all constituents necessary for full toxicity of the natural oils. The results show that essential oils of L. pungens and L. cubeba and some of their constituents have potential for development as botanical insecticides.