Submitted to: Journal of Chemical Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/7/1998
Publication Date: N/A
Citation: Interpretive Summary: The pineapple beetle, Carpophilus humeralis, is a pest of numerous crops in many warm weather regions, including the southern United States. Research on chemical attractants which could be employed in traps to monitor or control C. humeralis may provide effective and safer alternatives to current insecticidal control of this pest. An examination of volatiles from beetles living on host material led to the identification of three new compounds that are attractive to the beetles. These compounds, 4-ethyl-2-methoxyphenol, 2,5-diisopropylpyrazine (a previously unreported natural product), and 2-phenylethanol, are produced by microorganisms associated with the habitat of the beetles. In wind tunnel bioassays, these three compounds had enhanced attraction when combined with one another and increased trap catches of C. humeralis in field trials when tested in combination with other baits. The identification of these attractive compounds could play an important role in developing traps for the control of C. humeralis. This information should be useful to chemical ecologists, entomologists, and eventually, personnel involved in the control of these destructive insects.
Technical Abstract: Volatiles collected from oranges fed upon by Carpophilus humeralis(F.)(Coleoptera: Nitidulidae) of either sex were consistently more attractive than volatiles from beetle-free oranges in wind tunnel bioassays. Three attractants were identified from this system: 4-ethyl-2-methoxyphenol (1), 2,5- diisopropylpyrazine (2) (a new natural product), and 2-phenylethanol (3). Compounds 1, 2, and 3 had only slight activity alone but were highly synergistic with each other and with propyl acetate (PA), a fruity ester that is mildly attractive to Carpophilus beetles. Compound 2 was the most active in the wind tunnel; its threshold dose was 0.5 ng when PA was present. The structural specificity for these compounds was high. Twelve phenol analogs of 1 were tested, but only one of 2-methoxyphenol was more attractive than the control. Similarly, the analogs of 2,2-isopropylpyrazine and 2,6-diisopropylpyrazine were completely inactive. In the field, a combination of 1, 2, and 3 was not attractive by itself; but it strongly synergized attraction to fermentation volatiles, Carpophilus pheromones, or both. Compounds 1, 2, and 3 apparently have a microbial origin because all three were detected when the host fruit was pineapples instead of oranges, because they could occur in the absence of beetles, and because autoclaved pineapple began to produce the compounds after inoculation from an attractive piece of fruit. The study demonstrated that host location for this generalist species can be far more complex than responding simply to the bouquet of low molecular weight volatiles normally associated with fermentation.