Figure 1. Striped blister beetle adult feeding on a green pepper plant.
Credit: A. Varenhorst
Striped Blister Beetles
While checking on my garden this week I noticed that some heavily defoliated plants including green peppers, radishes, okra, and green beans. I was expecting to find large grasshopper populations present due to the jagged appearance of the holes left in the leaves. However, upon closer inspection I noticed that the insects responsible were actually striped blister beetles (Figure 1). The striped blister beetle is gregarious, which means it is commonly found in large groups within a small area. In this case, my 10 feet by 20 feet garden was infested by approximately 1,000-5,000 of these rather large beetles.
In addition to my garden produce, the striped blister beetles were also visibly defoliating a few of the weeds that I hadn’t removed from the garden. Although blister beetle adults are normally not a problem, they can cause significant defoliation when large populations are present. This is especially true in home gardens, where there are a limited number of plants.
We have also received reports of very large populations of the striped blister beetles in field margins. If these large concentrated populations move into crops such as soybean or alfalfa there is the potential for isolated areas of defoliation to occur.
As their name implies, striped blister beetles have black stripes that run the length of their yellow/orange abdomens. Striped blister beetles have an orange head with two oval markings that are separated by an orange line. The thorax, which is narrower than both the head and abdomen, is grey with two black lines on it. They have black antennae and gray/black legs. All blister beetles have elytra that are soft, and generally do not cover the end of their abdomen (Figure 2). Blister beetles contain a chemical referred to as cantharidin that is capable of producing painful blisters on human skin. Cantharidin is present in blister beetle hemolymph (blood), but can be exuded through reflexive bleeding when pressure is applied to the beetle.
Figure 2. Striped blister beetle adult. Credit: A. Varenhorst
In gardens, it may be possible to remove blister beetle infestations by hand. However, gloves should be worn as blister beetles contain cantharidin and picking them up may cause the chemical to be released. Ideally, one should use disposable gloves and be cautious not to touch the gloves to unprotected skin.
For severe infestations, insecticide powder/dust or spray may be used to reduce defoliation caused by blister beetles.
Blister beetle populations are often highest in areas where grasshoppers were dense during the previous year. Larvae of blister beetles consume grasshopper eggs, so managing grasshopper populations can be a preventative measure to reduce blister beetle populations in the future.