Ask a Master Gardener

blister beetle

Blister Beetles

8/27/22

I went out to my garden to look at my tomatoes today and they were a ton of striped insects all over them. They are destroying my tomatoes. What do I do? PS

The insect you are describing is likely a blister beetle. While there are thousands of different varieties of blister beetles, the most common one in Oklahoma is the striped blister beetle although we have been getting reports of black blister beetle activity as well.

Irrespective of their color, blister beetles share some common traits. Their most identifying features include a long body, slender thorax (neck), and a larger head. Typically, they range in size from between 1/3 to 2/3 of an inch in length.

In addition, doing damage to our garden crops, blister beetles can also be a problem in baled alfalfa for livestock. While the harvesting process can kill the blister beetles, the cantharidin in their bodies remains a problem in even dead blister beetles. Unfortunately, when livestock (particularly horses) feed on baled alfalfa that contains dead blister beetles, this can cause illness or even death in the livestock.

Adult blister beetles emerge in the spring. After emerging, the adults feed, mate, and the females lay clusters of eggs in the soil. These eggs will overwinter in the soil and emerge in late spring or early summer the following year. When the eggs hatch, they search for immature solitary bees or the eggs of grasshoppers to feed upon while in their larval stage. While feeding and growing they can look like grubs. Usually there is only one generation per year of blister beetles. When you discover blister beetles on your tomatoes, it can be a bit shocking because blister beetles like to congregate. One day you may not see any of them and then the next day your plant is covered with them.

In addition to their voracious appetite as adults, the cantharidin found in their bodies can cause rather unsightly blisters in humans. Because of this, when handling blister beetles or the plants playing host to blister beetles, it’s a good idea to wear gloves and long sleeves, probably even long pants.

To control blister beetles, you can manually remove them and destroy them while wearing protective clothing. On the chemical control spectrum, you can use an organic pesticide that contains pyrethrin. These are readily available in a variety of trade names at most garden centers. You can also use neem oil but be sure to test the neem oil on part of the plant first because horticultural oils in hot weather can sometimes damage your plants. Good luck.

You can get answers to all your gardening questions by calling the Tulsa Master Gardeners Help Line at 918-746-3701, dropping by our Diagnostic Center at 4116 E. 15th Street, or by emailing us at mg@tulsamastergardeners.org Photo Clemson University - USDA Cooperative Extension Slide Series , Bugwood.org