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Pear Ester – from Discovery to Delivery for Improved Codling Moth Management

Knight, A.L., Light, D.M., Judd, G.J.R. and Witzgall, P. (2018) Pear Ester – from Discovery to Delivery for Improved Codling Moth Management, pp. In. Roles of Natural Products for Biorational Pesticides in Agriculture, (ed., John Beck), American Chemical Society,

Abstract

The chemical ecology of codling moth, Cydia pomonella (L.), has been the subject of a worldwide research effort spanning five decades. The initial focus of this work was the characterization of codling moth sexual behavior and the identification of its sex pheromone, followed by the development of effective monitoring and management programs. Subsequently, a large body of work was dedicated to deciphering the chemical messaging systems that exist between both moth sexes and their apple host. However, it was from pear that a potent kairomone, pear ester, (E,Z)-2,4-decadienoate, was discovered, and surprisingly from field studies in walnut. Pear ester over the last decade has been the basis for the development of a range of commercial products that impact larval and adult behaviors and reduce levels of fruit injury. A review of codling moth and behavioral-active apple volatiles, the discovery of pear ester, and the development of useful technologies is provided here. A recounting of this story provides some considerations for the reader. First, that single odorants from a host (e.g. E,E)-α-farnesene and pear ester) and maybe not complex volatile blends that more thoroughly characterize a host odor, are fruitful targets to develop female attractants. However, practical concerns such as chemical stability and synthesis cost will limit the implementation of any discovery. Second, it is not clear what semiochemical evoked behaviors should be targeted to develop an effective lure, i.e. suitable host for sexual rendezvous, oviposition, or as a food source. Background odors from immature fruits and undamaged foliage are generally more dilute and less complex than from ripening fruits or damaged foliage. Thus, effective chemical signals need to be more intense and apparent to lure moths. Third, it appears that adding acetic acid to host plant volatile lures is effective in drawing moths into traps, perhaps as a short-range food cue. Fourth, it was a field bioassay with a pear volatile in a walnut grove that unveiled the power of pear ester. Only later did a series of physiological and molecular studies detail the evolved interplay of pear ester and sex pheromone in the brain of codling moth. It is possible that this more basic approach will in the future allow the purposeful discovery of new attractants which can aid pest management of tortricids and other pest species. But more likely, chemists and applied insect ecologists need to continue to identify, synthesize, and test the various semiochemicals that define the lives of insects.

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