Guess the Pest! Week #18 Answer: Western Bean Cutworm

Bill Cissel, Extension Agent – Integrated Pest Management;

Congratulations Bob Leiby for correctly identifying the moth as a western bean cutworm and for being selected to be entered into the end of season raffle for $100 not once but five times. Everyone else who guessed correctly will also have their name entered into the raffle. Click on the Guess the Pest logo to participate in this week’s Guess the Pest challenge!

Guess the Pest Week #18 Answer: Western Bean Cutworm
by Bill Cissel, Extension Agent, Integrated Pest Management and David Owens, Extension Entomologist

The western bean cutworm (WBC) is native to the western United States where it is considered a pest of corn and dry beans. Despite the name, they actually do not “cut” plants. Western bean cutworm are univoltine, meaning they have a single generation per year and overwinter as pre-pupa. In the spring, they pupate and adult moths emerge in early June. Female moths will lay eggs throughout July and August on both wild and cultivated plants. Field corn in the whorl stage prior to pollination is a preferred oviposition site. Eggs are typically laid on the upper leaf surface near the whorl in masses of 20-200 eggs which take approximatley 7 days to hatch. Larvae undergoe six instars before burrowing into the soil to pupate. Since the early 2000s, WBC has spread, causing economic damage as far east as NY, MI, OH, WI, and Ontario. Studies conducted in Nebraska and Iowa suggest an infestation averaging one larva per ear can cause yield losses reaching as high as 4 bu/A. Larvae bore through the side of the ear and open the ear up to mycotoxin-causing fungal colonization. Most Bt traits do not adequatley control this pest.

We first detected WBC in Delware in 2011 after capturing a few moths in a pheromone trap in New Castle Coutny. We captured 14 moths in 2012 and have not trapped for this pest since 2012 until 2018. This year, we have been monitoring 10 pheromone traps located throughout the state and have captured four moths to date. We will continue to monitor for this pest throughout the growing season but at this point, it appears that WBC populations remain low for us in Delaware. By comparison, states where western bean cutworm causes signficant injury to corn catch dozens of moths per week in a single trap.

2012 Western Bean Cutworm Trap Summary:

2013 Western Bean Cutworm Trap Summary:

Here is a link to a Fact Sheet from Purdue University with more detailed information on the identification, biology, and damage of the Western Bean Cutworm:

Fun Entomology Fact: It is not unusual to find an ear infested with multiple western bean cutworm larvae because they are not canabalistic like corn earworms.

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