I just wanted to do a little follow-up on the corn rootworm damage issue. I got a little too busy to follow my own advice. Several weeks have gone by and the beetle population increased while I wasn't paying attention. Below are two photos of ornamental sunflowers about 5-inches in diameter. The first photo is of a bloom that has been open for a about a day. The beetles don't seem to begin feasting on the sunflowers until they open up and begin producing pollen. As soon as the pollen appears, they also begin ravaging the outer ray petals -- as seen in the first photo below. This second photo is about a day later in our blistering hot, dry weather. Normally, the blooms will look great for a week or longer without the beetle damage. It is kind of interesting that a defense mechanism of these beetles is to just fold their legs up under themselves when disturbed. They simply allow their bodies to freefall to the ground. I have even played with some I find on the leaves and when you bother them, they will just begin rolling down the leaf until they fall off. You can take advantage of this habit by simply mixing up a little soapy dishwater in a small dish. Hold this dish under the blooms and they will fall right into it. I like to call this, The Dish of Death. (Heh, heh, heh.) This whole process only takes a few minutes in the garden and can be repeated as necessary. The Dish of Death IronBelly

I doubt that insect had any connection with the splits in the leaf. I'd suspect physical damage rather than pests: for example, hail striking the leaf, or wind blowing the leaf into a sharp edge of whatever is supporting the plant.

This is a little leaf-hopper commonly called a sharpshooter. It sucks the juices from plant stems. There are oodles of different species. BugGuide.net has 93 pages of them. You might be able to get a more specific ID by including such information as your location, and what kind of plants were nearby. Here is a link that might be useful: Sharpshooters on BugGuide

Guys, thank you for all your comments so far. I examine them carefully today again, it seems that their color change during their growth. They started with bright shiny red, then as they grow, they change to reddish with black or yellow lines, some of them even have a pair of small wings. I seriously doubt a water spray would do much to them, as I saw them fall onto ground to escape my fingers, then climbing back quickly. I guess I could try neem oil, but if these turn out to be some sort of beetles, would neem oil still work?