No. 14 Article 3/June 29, 2007

Captures of Western Bean Cutworm Moths?

People have already begun to report captures of western bean cutworm moths in pheromone traps in an extensive network of traps throughout the Midwest. Marlin Rice, extension entomologist at Iowa State University, confirmed a record-early capture of a western bean cutworm moth in a pheromone trap located near Sioux City, Iowa, on June 18, and he caught one himself in a trap near Ames, Iowa, on June 20. So the western bean cutworm is yet another insect that has shown up a little earlier than usual this year.

But--the most important question is whether the moths captured in traps are western bean cutworm moths. Regardless of the noted early captures of western bean cutworm moths, we caution about jumping to conclusions. Over the weekend of June 23, several University of Illinois Extension educators reported capturing large numbers of moths . . . but no one captured western bean cutworm moths. Thus far, the moths captured have been tentatively identified as yellowstriped armyworm (Spodoptera ornithogalli) and armyworm (Pseudaletia unipuncta), and possibly other species. According to experts at Great Lakes IPM, where we obtained our pheromone lures, there is a "common isomer" in the pheromone mixture that attracts certain nontarget insects to the western bean cutworm pheromone lure. There is no indication that there is a common isomer for western bean cutworms and yellowstriped armyworms, although there is a known common isomer for the western bean cutworm and the western yellowstriped armyworm (Spodoptera praefica), a species not known to occur in Illinois. It's also possible that some species are "blunder captures" merely because they are so prevalent, which could explain captures of armyworm moths (P. unipuncta).

In "Accurate Identification of Western Bean Cutworm Moths Is Crucial," published in issue 12 of the Bulletin (June 15, 2007), we emphasized the importance of moth identification.We reiterate the significance of accurately identifying moths captured in western bean cutworm pheromone traps because we do not want to misrepresent the importance of this pest, which is relatively new in Illinois. The entomologists at Iowa State University have added identification details to their Web site to emphasize the importance of accurate identification.

If you have established a western bean cutworm pheromone trap to monitor for moths, please make certain you are proficient at identifying the moths captured. Evidence to date suggests that more than one species of moth is being captured, so please verify the species before reporting captures.--Kevin Steffey

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