|Lerch, Robert - Bob|
Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/25/2012
Publication Date: 8/1/2012
Citation: Kessey, I., Barrett, B., Lin, C., Lerch, R.N. 2012. Electroantennographic responses of the lesser chestnut weevil curculio sayi (Coleoptera: Curculionidae) to volatile organic compounds identified from chestnut reproductive plant tissue. Environmental Entomology. 41:933-940. Interpretive Summary: Work conducted at the University of Missouri, Center for Agroforestry, has focused on identifying the optimal chestnut species for commercial yield in the Midwest U. S. and on establishing chestnut trees as a viable crop for landowners looking to diversify their production. The production of chestnuts in the United States is greatly affected by the primary pest insect, the lesser chestnut weevil (Curculio sayi). This insect is highly host-specific, as it has only been observed to feed and lay eggs on the genus Castanea (chestnut and chinquapin). Although chestnut weevil adults do not affect the health of the tree, they do lay their eggs inside the nuts and the feeding larvae can destroy the vast majority of the commercial crop harvest in a given year. In the spring, chestnut weevils have been observed to feed on flowers, while in the fall, they have been noted to feed and lay eggs on the forming nuts that are housed within spiked, protective burs. Chestnuts are known to produce characteristic odors from their flowers and nuts, but the burs have not been previously investigated for odor emission. Because the chestnut weevil is the key insect pest of chestnut, they pose a potential threat to the commercial establishment of chestnut plantations and improving our understanding of how to control these pests is needed. The overall objective of this work was to sample the volatile chemical profile of chestnut tissues (i.e., flowers, nuts, and burs) from the Qing cultivar of the Chinese chestnut and to measure the weevil's response to a sub-set of the identified volatile compounds. Results showed that a total of 59 volatile compounds were emitted from the chestnut tissues. The largest amount and variety of compounds was recorded from the chestnut flowers (36 compounds), with the nuts having the fewest detected (14 compounds). Bur tissue had a surprising amount and variety of compounds (24 total), sharing many similar compounds with flowers but none with nuts. Volatile compounds in the ester and ketone chemical classes elicited the strongest responses in the weevils. This research is part of an ongoing project to determine chestnut compounds that may play a role in the attraction of the chestnut weevil. This may, in turn, lead to advancement in monitoring and control practices for this insect pest through the use of odor compounds that can repel the weevil and reduce infestations. This research will ultimately benefit landowners interested in producing chestnuts by insuring that their investment will be protected from econmically damaging chestnut weevil infestations that could undermine the establishment of this new enterprise.
Technical Abstract: The primary insect pest of the developing chestnut industry in the central United States is the lesser chestnut weevil, Curculio sayi (Gyllenhal), which is a specialist on only Castanea trees. Recent research has shown this insect is attracted to and feeds upon the reproductive tissues of the chestnut tree, including the flowers, burs and nuts. In this study, the major volatile components emanating from the chestnut’s reproductive tissues were sampled using solid phase micro extraction (SPME) and static headspace analysis. A total of 59 compounds from these tissues were separated and identified using GC-MS and authenticated reference standards. The majority of compounds identified from the bur and nut tissues were esters (60.2 and 67.4 percent, respectively). The majority of compounds identified from catkins were alcohols and benzenoids (53.2 and 19.8 percent, respectively). A subset of those compounds identified from the chestnut plant tissues was used in electroantennogram (EAG) testing to determine the insect’s electrophysiological response to host-generated volatiles. This study identifies the major components of the volatile profile from several important chestnut plant tissues, and was the first to report the volatile compounds from bur tissue. The identification of the major volatiles emanating from chestnut tissue, as well as the associated insect response, are both critical to the successful utilization of these host-plant volatiles as attractants in the development of a semiochemical-based monitoring trap for C. sayi adults.