Watch for Blister Beetles in Alfalfa

 

 

We are receiving several reports of blister beetles in South Dakota. While the larvae of these insects are considered beneficial due feeding on grasshopper eggs, the adults can cause defoliation as well as health issues for livestock. Blister beetle populations will typically follow areas that had large grasshopper populations during the previous growing season. Defoliation caused by blister beetle adults is usually minor. However, the main concern with these insects is that the adults contain a chemical known as cantharidin that is capable of producing painful blisters. Cantharidin is present in blister beetle hemolymph (blood) but can be exuded through reflexive bleeding when pressure is applied to the beetle. This chemical can prove fatal when ingested in large quantities by livestock, especially horses, due to the irritation it causes in the gastrointestinal and urinary tracts of the animals.

 

Although there are several species of blister beetles found in South Dakota, they vary in their toxicity to livestock and their ability to defoliate crops (Table 1). The three-striped blister beetle contains a higher concentration of canthardin, while the margined blister beetle is noted for having the greatest potential to cause severe defoliation.

 

 

 

 

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).