Fumigant toxicity of plant essential oils to Thrips palmi (Thysanoptera: Thripidae) and Orius strigicollis (Heteroptera: Anthocoridae)

The fumigant toxicity of 92 plant essential oils to adult Thrips palmi Karny (Thysanoptera: Thripidae) and Orius strigicollis Poppius (Heteroptera: Anthocoridae) was examined by using a vapor phase toxicity bioassay and compared with those of dichlorvos, emamectin benzoate, spinosad, and thiamethoxam, four commonly used insecticides. Responses varied according to oil type and insect species. As judged by 24-h LC50 values, pennyroyal oil (2.63 mg/liter air) was the most toxic fumigant and was 23.6-fold more toxic than dichlorvos (62.09 mg/liter air) against adult T. palmi. Potent fumigant toxicity (LC50, 11.03-19.21 mg/liter air) was observed in armoise, basil, cedarleaf, coriander, cypress, howood, hyssop, marjoram, myrtle, niaouli, rosemary, and sage (Dalmatia) oils. Neither emamectin benzoate, spinosad, nor thiamethoxam exhibited fumigant action. Against adult O. strigicollis, dichlorvos (LC50, 6.3 x 10(-6) mg/liter air) was the most toxic fumigant, whereas the LC50 values of the 13 essential oils ranged from 17.29 to 158.22 mg/liter air. O. strigicollis was 1.4-22.1 times less susceptible than T. palmi to the essential oils. The essential oils described merit further study as potential fumigants for the control of T. palmi in greenhouses.