All mustards are not created equal: Optimizing trap cropping for the harlequin bug (Murgantia histrionica, Hahn) on collard

Differences among crop varieties are sometimes based on their constitutive or derived biochemical composition, generally centered on their semiochemical attributes. These attributes enable some varieties of crop plants to be more attractive to insects, and thus useful as trap crops in pest management. Many workers on cruciferous crops use trap crops to reduce the use of insecticides; for example, mustard (Brassica juncea [L.] Czern) trap crop has been proposed as a viable alternative to pesticides for control of the harlequin bug, (Murgantia histrionica, Hahn) on collard. Mustard is available in different varieties which vary in their composition and levels of glucosinolates, the sulfur-rich, N-containing compounds that are widespread among the Brassicaceae. These differences make use of crop variety/accession name imperative in trap crop recommendations. In studies using laboratory bioassays to develop a rapid method to identify suitable trap crops for the harlequin bug on collard we confirmed the reported preference of mustard by this insect; this was based on its distribution and feeding damage (necrosis) using a preference index (PI). In addition, we found interesting nuances in preference, both within the mustards and among the other plant varieties used in the study. We present initial results on the entomological, molecular and biochemical evidence which lead us to conclude that 1) laboratory assays can be used to quickly identify potential trap crops; 2) mustards are not equally attractive to harlequin bugs; 3) it is important to specify the crop variety or cultivar when making recommendations for mustard trap crop deployment.