The fumigant toxicity of 66 plant essential oils to Plutella xylostella (L.) larvae and Cotesia glomerata (L.) adults was examined using a vaporphase toxicity bioassay and compared with that of dichlorvos. Responses varied according to oil and insect species used. Based on 24 h $LD_{50}$ values, pennyroyal oil [10.77 mg/filter paper (4.25 cm diameter)] was the most toxic fumigant, followed by rosemary and sage (Dalmatin) oils (15.15 mg/paper). Potent fumigant toxicity was also produced from armoise, buchu leaf, cedarleaf, coriander, eucalyptus, howood, lavender, myrtle, niaouli, peppermint, and rosewood oils ($LD_{50}$, 21.29-27.31 mg/paper). All essential oils were less effective than dichlorvos ($LD_{50}$, 0.52 mg/paper). Against adult C. glomerata, dichlorvos ($LD_{50}$, 0.03 mg/paper) was the most toxic fumigant, whereas the $LD_{50}$ values of the 14 essential oils ranged from 1.59 to 8.51 mg/paper. Based on selective toxicity ratio (STR, P. xylostella $LD_{50}/C$ glomerata $LD_{50}$), the 14 essential oils (STR, 2.5-14.5) are more selective than dichlorvos (STR, 17.3). The essential oils tested merit further study as potential fumigants for the control of P. xylostella in greenhouses because of their selective toxicity to adult C. glomerata and their much greater activity as a fumigant.