|RAINES, GLEN - University Of Georgia
Submitted to: Phytochemistry Letters
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/30/2015
Publication Date: 11/21/2015
Citation: Potter, T.L., Olson, D.M., Ni, X., Raines, G.C. 2015. A re-examination of corn (Zea mays L.) ear volatiles. Phytochemistry Letters. 14:280-286. https://doi.org/10.1016/j.phytol.2015.10.026.
Interpretive Summary: The corn earworm is one of the most destructive corn pests worldwide. Control typically involves numerous insecticide sprays during growing seasons. Alternate tools are needed for insecticide resistance management, to reduce the potential for environmental damage associated with pesticide use, and to reduce costs. To this end a better understanding of how female adult moths are attracted to and select maturing corn ears to lay eggs is needed. Since the adults feed, mate, and lay eggs at night, it has often been hypothesized that volatiles emitted by maturing corn ears, in particular corn silk, serve as ear worm moth attractants. We used a novel technique to capture and analyze volatile chemicals emitted by corn ears in a south Georgia corn field during silk production. Thirty-six compounds were identified in collections. The three principal constituents had not been identified in prior investigations. Their structure suggests that they are formed from precursor compounds as the ears ripen. Given this they appear to good candidates for further testing to determine if they attract earworm moths.
Technical Abstract: Helicoverpa zea (Boddie) is a major insect pest of corn and other agricultural crops. In corn adult moths commonly lay eggs on silk of ripening ears. After hatching, larvae feed on silk and developing kernels. This reduces crop quality and may increase fungal infection and mycotoxin production. Substantial economic loss may result. Insecticides are commonly used to manage this pest. An improved understanding of semiochemicals that control adult behavior is needed to develop alternative control measures. In this study, overnight SPME collection of volatiles from corn ears enclosed in Teflon bags in the field at two stages of development were made. C8 to C10 aldehydes, a C8-alcohol, C6 to C9 alcohol acetates, and numerous monoterpenes, sesquiterpenes, sequiterpene alcohols, and geosmin were identified after thermal desorption and GC/MS. Structural assignments of the alcohol acetates, Z-3-hexenyl acetate, 2-heptyl acetate, 2-nonyl acetate, and 4-nonyl acetate, the monoterpenes, a- and ß-ocimene, and geosmin were made by analysis of standards that were purchased or prepared in the laboratory. All other assignments were based on published Kovat’s retention time indices (KI) and mass spectra. Pair-wise comparison of the relative amounts of each component between two groups of corn ears defined by silk weight did not identify significant differences thus it is unknown whether or not silk weight impacted volatile emission composition and rate. To our knowledge three compounds detected in SPME collections, 2-heptyl acetate, 2-nonyl acetate, and 4-nonyl acetate have not been previously reported in corn ear or silk volatiles. Their impact on the flight response of gravid earworm females was evaluated in a flight chamber. No significant response to the individual compounds or a blend of all three was observed. Thus, their impact on moth behavior remains uncertain.