The leafhopper population exploded in Valley Springs this spring, June 2017. Many people were calling in, often referring to it as a ‘plague’, as the numbers were so great. Nate Spring, our service technician, reported that he was commonly seeing the leafhoppers near cottonwood trees, and that many of the houses inundated with the leafhoppers had cottonwood trees. The population died down after a couple of weeks, although Nate reported that they could still be found at the base of the cottonwoods for a few more weeks.
The species of leafhopper was identified by Dr. Alessandra Rung of CDFA, as Euscelidius variegatus, sometimes called Euscelis variegatus, which is a European exotic. It can transmit a variety of plant pathogens, so it probably feeds on a wide variety of plant types. I want to thank Dr. Lynn Kimsey for getting this identification process done.
Some internet references to Euscelidius variegatus: