One of the questions I have received in the last week has been about an inch-long bug on tomato plants.

Though there are several members of this family that can cause damage, the Striped and Gray Blister Beetles are the most common. These beetles also like beans, peas, potatoes, and other vegetables. The adult stage causes the damage, not the larvae. The beetles tend to move in swarms and can cause a great deal of defoliation but may not stay in one area for very long.

Blister beetles, commonly referred to as blister or oil  beetles, belong to the family Meloidae. Species vary in size and color but are easily recognized by their elongated,  narrow and cylindrical body shape. The neck is accentuated by a constriction between the back of the head and  the narrow anterior end of the thorax. Although adult blister beetles feed on vegetation, the larvae of common species (genus Epicauta) feed on grasshopper eggs.

Blister beetles pass the winter in a pseudopupa stage and then go through a final molt in the spring. After a short period of activity, the larva enters the true pupal stage with the adults emerging midsummer.

Blister beetles have long, slender bodies with a relatively large head. These insects release a caustic substance, called cantharidin, when crushed that can raise blisters on the skin.

The threestriped blister beetle, Epicauta lemniscata, contains especially high levels of cantharadin, which is toxic to horses. The ashgray blister beetle, Epicauta fabricii, often aggregates on blooming puncturevine.

Often beetles will move on in a day or two. If beetles are handpicked, be sure to wear gloves. A number of stomach insecticides, such as cyfluthrin (Bayer Vegetable & Garden Insect Spray), permethrin (Bonide Eight and Hi-Yield Lawn, Garden, Pet and Livestock Insect Control) and gammacyhalothrin (Spectracide Triazicide) are also effective for control.


— Scott Eckert is a Kansas State Research and Extension agent for Harvey County. Horticulture is his specialty. The Harvey County Extension Office can be contacted at 284-6930.