Ester components of aggregation pheromone ofDrosophila virilis (Diptera: Drosophilidae).

The male-produced aggregation pheromone ofDrosophila virilis was found to contain five ester components, in addition to a previously identified hydrocarbon, (Z)-10-heneicosene (Z10-21). The five esters were: the methyl, ethyl, and 1-methylethyl (isopropyl) esters of 2-methyl-(E)-2-butenoic (tiglic) acid and the methyl and ethyl esters of hexanoic acid. The esters were not detected in females. Each ester was active by itself in laboratory bioassay tests, and each increased the number of flies responding toZ10-21 ca. 4-5 times. In comparisons among the five esters at 10 ng per compound, ethyl tiglate was the most active, and methyl tiglate, the least. No mixture of esters was found to be significantly more active than ethyl tiglate alone. In a doseresponse study, bioassay activity increased with dose for both ethyl tiglate andZ10-21. Newly emerged males did not have detectable levels of the esters. All five esters increased as sexual maturity was approached. Ethyl tiglate and ethyl hexanoate were the most abundant in mature males, usually over 15 ng per individual. Ratios among the esters were variable. Male flies also contained an as yet unidentified attractant(s) still more polar than the esters, which was synergistic with the esters and hydrocarbon. Food odors also synergized the synthetic compounds.