Pear ester - from discovery to delivery for improved codling moth management

Authors: Knight, Alan; Light, Douglas

Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: 5/15/2018
Publication Date: 8/28/2018
Citation: Knight, A.L., Light, D.M. 2018. Pear ester - from discovery to delivery for improved codling moth management. In: Beck, J., Rering, C.C., Duke, S.O., editors. Roles of Natural Products for Biorational Pesticides in Agriculture. Washington, D.C.: ACS Publications. p. 83-113. https://doi.org/10.1021/bk-2018-1294.ch008.
DOI: https://doi.org/10.1021/bk-2018-1294.ch008

Interpretive Summary: More than a decade of collaborative research among entomologists at the USDA, ARS, Temperate Tree Fruit and Vegetable Research Unit, Wapato, WA and the Western Regional Research Center, Albany, California helped to develop pear ester as a new lure for monitoring adult moths, as a spray to enhance insecticides targeting larvae, and within dispensers for improved mating disruption of codling moth. This chapter reviews this research and a large body of international studies that followed its discovery. Consideration of the associated literature on other host plant volatiles similarly investigated but found to be ineffective is presented to highlight several unique aspects of pear ester in the biology of codling moth. The review suggests that the serendipity of the pear ester discovery likely does not provide a blueprint for future discoveries of new host plant volatiles that can impact pest management of other tree fruit pests.

Technical Abstract: The chemical ecology of codling moth, Cydia pomonella (L.), has been the subject of a world-wide research effort resulting in hundreds of publications in peer-reviewed journals. The initial focus of this work was characterization of the sexual behavior of the moth and identification of its sex pheromone, followed by development of effective monitoring and management programs. Secondly, a large body of work has attempted to decipher the chemical messaging between both sexes and its apple host. Yet, it was from pear that a subtle yet potent kairomone, pear ester, (E,Z)-2,4-decadienoate, was discovered, and has been the basis for a range of commercial products which have synergized the effectiveness of the sex pheromone. 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, primary odorants from the host (E,E)-a-farnesene and pear ester) and maybe not the complex blends that uniquely characterize a host, 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 chemical signals should be identified 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.