The semiochemistry of the common North American pest of crucifers, Murgantia histrionica (Hahn) (the harlequin bug), and two related European species, Eurydema ventrale L. and E. oleraceum L., was investigated. The metathoracic scent glands of these warningly-colored stink bugs (Pentatomidae) are smaller than the scent glands of most cryptically-colored pentatomids, and the secretions from the scent glands of Murgantia and Eurydema species include two heretofore unknown natural products: (2E,62E)-octadienedial and (2E,6E)-octadiene-l,8-diol diacetate. It also was discovered that when harlequin bug adults are squeezed, they expel a frothy fluid from the margins of the prothorax with a distinctive odor due to the presence of 2-sec-butyl-3-methoxypyrazine and 2-isopropyl-3-methoxypyrazine. The presence of alkylmethoxyprazines in the expelled fluid of harlequin bugs extends the known distribution of these compounds to include the Heteroptera, and strengthens the argument that this class of pyrazines constitute a universal warning ordor equivalent to the color red as a visual warning signal.

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