Blister beetle troubles

ImageBlister beetles can sometimes occur in large numbers in and around crop fields. They are attracted to blooming weeds, garden plants and crops (including alfalfa and soybean).

Blister beetles are a common feature of summertime in the region and can be both a crop pest and a home garden pest. Recently, reports have come in from several counties in SC and SW Kansas where these are being encountered in gardens and alfalfa fields.

Blister beetles are relatively large beetles (.5-1 inches) with long, sometimes brightly colored abdomens.  There are over 100 species in the region but only a few are commonly encountered.  These beetles are appropriately named; cantharidin, a substance found within the blister beetle, can cause painful blistering on exposed skin if someone is to accidentally crush or harass the beetle.   This same substance can even be deadly to cattle, especially horses, if the animals are to eat the beetles while feeding on hay.  Different species of blister beetles have differing levels of this cantharidin. Male beetles produce this toxic chemical and will transfer it to the female after mating.

Adult beetles in the garden feed on a wide variety of foliage and flowers; large numbers can easily defoliate small garden plants. Interestingly, blister beetle larvae can be beneficial in that they feed on the eggs of grasshoppers (another summertime garden nuisance).  While the adult beetles can sometimes be found on or in the home, they pose no structural hazard.  For the reason mentioned above, care should be taken when removing them from or off of the home.  There are a variety of chemical control methods for blister beetles if their numbers become a problem in the garden, however these beetles are very mobile and new individuals easily find the garden.  On the positive side, their larger size makes them easily detected in the garden; many gardeners employ simpler methods of blister beetle control, such as hand vacuuming large numbers off of plants or knocking individuals into a bucket of soapy water. 

To reduce blister beetle numbers in alfalfa fields, cut the alfalfa before it enters bloom stage and maintain a weed free field. The first cutting will general not have blister beetles, but caution should still be exercised when feeding this to horses. Treating infested alfalfa fields with a blister beetle labeled insecticide will kill the beetles, however the dead beetles left in the field are still toxic!

ImageA Margined blister beetle (Epicauta funebris), one of the more commonly encountered blister beetles.

More information on blister beetles can be found here:

http://www.asi.ksu.edu/doc5062.ashx

http://www.hfrr.ksu.edu/doc1589.ashx

http://ianrpubs.unl.edu/pages/publicationD.jsp?publicationId=628

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