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Darkling/Mealworm vs. Blister Beetles

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By Rick Greenwell

This is a very informative article for Dr. Lee Townsend, University of Kentucky Entomologist and I want to share it with you.

Finding beetles in alfalfa hay raises an immediate red flag. Are they blister beetles? If not, what are they and are they harmful? Darkling beetles or mealworm beetles are relatively common in stored hay and resemble the black blister beetle. These insects feed on broken kernels and fines so they are common around barns and hay storage areas.

They avoid light so they can be found under, in, or between stacked hay bales. Darkling beetles do not contain cantharidin, the toxin in blister beetles; they are not harmful.

Mealworms, the larval stage of the darkling beetle, are common in stored or spilled grain or feed, where they eat broken kernels and fines. Adults often wander breeding site and enter stacked hay so it can be hard to find the source of the infestation.

Sanitation is the key to dealing with darkling beetles but it can be difficult to find and eliminate all breeding sites of these insects. Fortunately, their development is relatively slow so it takes time for large numbers to develop. Brooms and shop vacs need to be used to clean all accessible fines.

Infestations in stored bulk feed are more difficult to address, depending on the amount that is present, how quickly it will be used, and time of year.

It may be best to feed out the supply and thoroughly clean the storage area and surroundings before re-filling it. A pyrethrin spray labeled for use in feed storage areas after clean up will help to eliminate surviving insects.

Information on blister beetles in alfalfa is available in this factsheet - www.ca.uky.edu/entomology/entfacts/ef102.asp

Root mealybugs were found on a poor stand of stunted alfalfa seeded this spring in Fleming County. The previous crop was soybean. Mealybug-iInfested plants are generally stunted and may be chlorotic, depending on the numbers of insects present.

These mealybugs are sap feeders on the roots of many legumes: alfalfa, red clover, white clover, and soybean. They also have been found on the roots of corn, Johnson grass, sorghum, curly dock, milkweed and plantain.

It is likely that the insect is widely distributed in the state and high populations will be associated with continuous legumes or undisturbed pastures. Rotation to corn or tillage are most likely control options.

The species is listed from all of our neighboring states and seems to occur over much of the eastern US.