Leaf eating beetle eating Clematis leaves
The past three summers (typically mid July), I've had these beetles each the leaves on one of my clematis plants. I pick off the hundreds of bottles and put them in soapy water. However, I think this problem is systemic and wonder what I can do to prevent a reoccurrence next year.
I've attached photos of the crime scene and the battles.
Arapahoe County Colorado
These are Clematis blister beetles (Epicauta cinerea).
You can continue to pick them or knock them into a bucket of into soapy water (use gloves!).
Or, at first occurrence, spray them with an insecticide containing spinosad, pyrethrin or carbaryl (trade name Sevin). Note that carbaryl is HIGHLY toxic to honeybees, so do not spray any leaves that might also contact flowers attracting honeybees. In any case, read and follow label directions for any insecticide you choose.
Robert, thank you for your response and identifying the beetle. The soapy water is very effective but is there anything I can do to treat the soil to avoid another occurrence next year?
No. At least nothing really feasible. Blister beetle adults do not lay all their eggs in soil immediately under their host plant.
Blister beetles are pests as adults and beneficial insects as larvae (grubs). Grubs feed on grasshopper eggs in the soil; "successful" grubs that are able to feed on enough grasshopper eggs will become adults, then fly to and aggregate on their favorite host plant (clematis, alfalfa, others). You'd have to treat soil for a pretty large area (a square mile?) to have any hope of eliminating this insect before it pupates to an adult.