Submitted to: International Symposium on Fruit Flies of Economic Importance Stellenbosh, South Africa
Publication Type: Proceedings
Publication Acceptance Date: April 19, 2002
Publication Date: N/A
Interpretive Summary: Trapping of fruit flies is essential to monitor populations for control purposes and to assess and enforce quarantine issues. Trapping of melon flies has been less efficient than desired, largely because of limitations in the baits. This paper describes the development of a more effective lure that is likely to replace the currently used cuelure, and also discusses factors that define effectiveness in a melon fly attractant.
Technical Abstract: The melon fly, Bactrocera cucurbitae, is a world-wide pest of great economic importance, and strenuous efforts are continually being made to prevent its establishment in the continental U.S. and certain other parts of the world where it is not currently found. A limitation of current monitoring (trapping) methodology is the effectiveness of available attractants. The most attractive compounds for melon fly seem to be the naturally occurring raspberry ketone, (4-(4-hydroxyphenyl)butan-2-one) and its acetate which is commonly known as cuelure. The general consensus has been that these two compounds suffer not from lack of intrinsic attractiveness but simply are not volatile enough to be highly attractive over long distances. Because of the inherent attractiveness associated with the raspberry ketone/cuelure structures, we synthesized and evaluated a series of related compounds wherein we attempted to retain structural features essential for attractancy while maximizing volatility. One approach consisted of a series of fluorinated analogs, since it is known that in some cases, highly fluorinated compounds can be considerably more volatile than their non-fluorinated counterparts. Unfortunately, none of the fluorine-containing analogs tested were nearly as attractive as cuelure, and many possessed no measurable attractancy at all. We also prepared and tested a few compounds in which the acetate of cuelure was replaced by another group. Specifically, the formate ester and trimethylsilyl (TMS) ether of raspberry ketone were synthesized. The former had been synthesized earlier by Metcalf and coworkers, who found it to be a superior attractant but did not pursue its development, presumably because of reservations concerning its hydrolytic stability. Silyl ethers of raspberry ketone have not been previously tested. In short term tests, the TMS ether of raspberry ketone was as attractive as cuelure. This compound is very sensitive to moisture, however (it¿s rapidly hydrolyzed back to raspberry ketone), and its utility for longer term applications seems limited. On the other hand, raspberry ketone formate consistently outperformed cuelure as a melon fly attractant over periods of at least four weeks. Hydrolytic stability is better than predicted, and it is currently being evaluated under a variety of test conditions. Esters and other derivatives of raspberry ketone occupy a unique status in that their hydrolysis product, raspberry ketone itself, is an effective attractant. Thus a functional group that would aid in volatilization or release of an attractant from a matrix, and subsequently be lost due to hydrolysis by atmospheric moisture could be an element of formulation strategy.