Abstract
2-Phenylethanol was identified as a potent attractant for onion and seed-corn flies by chemical analysis of aged onion pulp, which was highly attractive for these insects in the field. After filtration, steam-distillation and extraction with ether, the attractive compounds in the aged onion pulp were found to move into the acidic and neutral fraction. Analysis of the neutral fraction by GC and GC-MS revealed the presence of iso-butyl alcohol, ethanol, ethyl acetate, iso-amyl alcohol and 2-phenylethanol, the last two compounds being the major constituents. Only 2-phenylethanol showed moderate attractancy to the onion fly in laboratory bioassay. As 2-phenylethanol alone could not explain the high attractancy of aged onion pulp, some unidentified minor constituents were considered to be important in this manifestion. Despite the moderate attractancy of 2-phenylethanol in laboratory test, this compound showed high attractancy to onion and seed-corn flies in the field. The attractancy to the onion fly was about the same as the fresh onion pulp, which had about half the attractancy of the aged onion pulp. Attractancy to the seed-corn fly, particularly to the male, was quite high. 2-Phenylethanol caught 6 and 3 times as many male and female seed-corn flies as the fresh onion pulp, respectively.
