Grasshoppers Attract Beetles?

 

Dark gray form of the clematis blister beetle.
Photograph courtesy of Ginny Sawyer.

I thought last year would be the end of the carnage in my yard, never to happen again. Overnight, blister beetles stripped an entire clematis vine. They also ate up an Anemone Hupehensis ‘September Charm” in the middle of a shade garden and didn't touch any other specimens. Tried diatomaceous earth which didn’t work very well so I reluctantly resorted to some chemical insect spray. I thought I had eliminated them and the plants started to recover, but the beetles came back two weeks later chewing on both the same plants. Little did I know that this attack was related to the number of grasshoppers I had the year before!

I had contacted Dr. Whitney Cranshaw, Emeritus Professor of entomology at Colorado State University and he wrote back: "I suspect the blister beetle involved is the "clematis blister beetle."  He recently wrote a sheet on this at:  https://webdoc.agsci.colostate.edu/bspm/arthropodsofcolorado/Clematisblisterbeetle.pdf

Some interesting highlights from Dr. Cranshaw's paper about the clematis blister beetle:

• Larvae develop by feeding on the eggs of grasshoppers. Adult clematis blister beetles lay their eggs during mid-late summer in soil, at sites utilized as “egg beds” for grasshoppers.
• The newly hatched blister beetle larva (known as a triungulin) is tiny, but highly active and burrows into the soil. Upon finding an egg pod it then molts to a sedentary, grub-like form that begins to feed on the eggs. There then follow a series of additional actively feeding larval stages during which a total of between 21-27 grasshopper eggs is typically consumed. When the sixth instar is reached, a dormant (diapause) larva is produced that is the overwintering stage. In spring development resumes, pupation occurs, and the adults emerge in early summer.
• Since immature stages of the clematis blister beetle feed on egg pods of grasshoppers, the numbers of adult beetles loosely track the abundance of grasshoppers in the vicinity that were laying eggs the previous summer. Adults feed on foliage of various plants, but Clematis is a very common host plant and the one on which high populations are most often seen. Most other hosts on which this insect feeds are in the Ranunculaceae, including Anemone, Delphinium (larkspur), and pasqueflower. 

Why are they called blister beetles? Because they produce a highly toxic compound called Cantharidin which can irritate the skin and produce blisters so be careful removing them. See Dr. Cranshaw's paper for more information about controlling them in your garden.

This year they're back again, although I was carefully watching my clematis vine to catch them early. Early application of spinosad did the trick. Here is one of the villains:

Epicauta cinerea Clematis Blister Beetle

Photo: Nancy Shepard