Bryan Jensen, UW Extension
Chris Allen just contacted me about some suspected cereal leaf beetle damage in wheat. I’ve talked to a few more people and they also mentioned similar damage. Damage, although mostly on the flag leaf, doesn’t appear to be of economic concern.
Cereal leaf beetles are not an insect that we have a lot of experience with. At least not in recent history. Perhaps there was some economic damage when they were first introduced to the Midwest in the early 1960’s, but I suspect several predators and/or parasitoids have kept their numbers low. Matter of fact, I’m not sure I can ever recall someone having to control them in the past. However, knowing what causes the damage may be useful itself.
The adult cereal leaf beetle is approximately ¼ inch long and slender. They have a brightly colored orange head and thorax and dark bluish (almost metallic) wing covers. The larvae are yellowish to brown in color and can be slimy because they will cover their body with fecal material. This can give them a slug-like appearance. However, you will see a distinct head, no antennae and 3 sets of legs on cereal leaf beetle larvae.
Cereal leaf beetles overwinter as adults and are limited to one generation/year. Their host range includes most small grains as well as other grasses. Damage is very clear-cut and diagnostic. Both adults and larvae will feed on the same plant and leave long narrow feeding scars often with the cuticle intact. This “window paneing” may coalesce if damage is sever.
Published economic thresholds vary. To give you a perspective, Penn State suggests 1 larvae/4 tillers, North Dakota State suggest three larvae/plant and Michigan State suggests 1 larvae/flag leaf. Having different economic is not that unusual as researchers use the natural population available. All states, however, stress the importance of protecting the flag leaf from significant damage.
Photo Credit: Kansas Department of Agriculture Archive, Bugwood.org