Most recently reviewed by: Pat Porter (2018)
Common Name(s): Blister beetle, other blister beetle species, striped blister beetle
Blister beetles are in the insect family Melòidae. They can be found in many different colors and several sizes and body shapes. Their most distinctive feature is the narrow thorax and wider head, a feature that separates them from the majority of other beetles. Most blister beetles have an elongate, cylindrical abdomen, but some look very different. A few species have rounded “ball-like” abdomen or short wings and a larva-form abdomen. All blister beetles, however, have the distinctive narrow “neck” which contrasts with the broader head and abdomen.
The striped blister beetle, Epicauta vittata, has the typical cylindrical body shape. Beetles are from 1/3 to 2/3 inches long. Their bodies are tan to amber colored with three dark (black) stripes on each wing cover (elytron). The two stripes in the middle of the back continue onto the throrax and often onto the head. The eyes are black or dark grey.
The hemolymph (blood) of blister beetles contains a blistering substance called cantharidin. When beetles are alarmed or disturbed, they secrete blood and cantharidin. Contact with cantharidin causes blistering and tissue damage.
Origin and Distribution
Blister beetles are native to many parts of the United States. There are some 7,500 species worldwide and about 100 species in Texas http://texashighplainsinsects.net/insect-of-the-week/2013/5/21/blister-beetles-may-24-2013 . Epicauta vittata can be found in the eastern U.S. and Canada.
Habitat & Hosts
Blister beetle adults feed on broadleaf plants, especially those in the Amaranthaceae, Asteraceae, Leguminosae and Solanaceae. Most adults feed only on flower parts, but some eat leaves as well.
In the larval stage, blister beetles prey on the immature stages of solitary bees or on the eggs of grasshoppers in the family Acrididae (short horned grasshoppers), common grasshoppers in found pastures and grasslands.
There have been cases where people living adjacent to tracts of pasture or grassland have been inundated with blister beetles, so it is not necessary to have alfalfa or other host crops present in order to have a significant blister beetle infestation.
Blister beetles spend the winter in the larval stage. They pupate in the spring, and after about 2 weeks adult blister beetles emerge in the early summer. Adults feed, mate and females begin laying clusters of eggs in the soil. The eggs hatch as tiny, mobile triungulin larvae which seek out their bee or grasshopper hosts. Upon finding hosts on which the can feed, the larvae take on an increasingly grub-like appearance, before pupation in the spring. Most blister beetle species have only one generation per year. https://texasinsects.tamu.edu/hemiptera/blister-beetle/
ManagementIf you live in the State of Texas, contact your local county agent or entomologist for management information. If you live outside of Texas, contact your local extension for management options.
Alfalfa fields should be monitored from June through September for the presence of blister beetles. Cuttings before June are at lower risk of being contaminated by blister beetles. Monitoring can be done quickly and efficiently with a sweep net.
Blooming fields are very attractive to blister beetles, so fields should be managed such that cutting occurs at early (5-10%) bloom.
Since several some species of blister beetles – particularly striped blister beetle – congregate or form clusters of many individuals in a small area of the field, areas where clusters are found can be left unharvested, or sprayed with a “spot-treatment” insecticide. Be aware of the pre-harvest intervals of insecticides used near alfalfa harvest.
Most modern hay production equipment is equipped with crimpers which crimp alfalfa stems, shortening the drying time for the hay. Crimpers can kill blister beetles and cause them to remain in the hay. Swathing hay without crimping it allows most of the blister beetles to escape the hay and not end up in baled hay. Raking hay is helpful in dislodging dead blister beetles before baling.