Why don't you inspect your plants in the early evening and then later towards 9PM. If you have slugs or snails they will also munch on the leaves so you should have chewed up leaves.

Well, I've lost a dahlia to a much more easily identified suspect - DH! He feels really badly about it. I had too many tubers for the space I planned, so I popped one in the ground in the yard near a Gardenia that is still small this year, and he didn't know it was there (despite the 4'tall stake right next to it). I was told after this incident that fluorescent tags should now be applied to any new plants not contained in clearly marked and bordered beds. Ha Ha. He reduced it to 4" stalks with no foliage using the weed whacker. I'm hoping that it recovers, but I'm not going to hold my breath...just thought you guys would get a laugh out of this one. He's cuter than the squirrel in the photo, so I'm going to let him live.

It could be a flea beetle if it looks like BB's have been shot though the leaves. They are little black beetles that jump like fleas and are usually found on the underside of the leaves. Sevin will control them and just about any other bug that eat on your dahlias. It will kill the bees too so you don't want to use it on blooms.

After searching to hopefully find a non lethal way to get rid of the Four Lined Plant Bug, to no avail to speak of, I did run across this newspaper advice column in the link below. The second Question and answer contributes to your problem with the four lined plant bug. A little late for this year, but plenty of time to get ready to attack them this fall. As they say prevention is the best medicine. Here is a copy of that question and answer. I hope they don't mind and if the moderators feel it best to delete it, please leave the link. "QI have a huge area that is planted with Russian sage, mums as well as a few other perennials. The problem is that almost all the plants have these tiny brown circles all over the top part of the leaves. I don't know if it's a disease or an insect. Chuck, Fair Oaks Based on what you described, you may have a fungus or you could possibly have what we call four-lined plant bugs. They are easily identified by the four black stripes running down their back. They have a range of hosts, including fruits, vegetables, flowers, herbs and cucurbits. The associated damage consists of spots that look similar to fungal disease spot and can be misidentified as such. With piercing/sucking mouthparts, the four-lined plant bug removes the plant's chlorophyll. A toxin present in their saliva is also secreted during feeding that digests the components responsible for holding the plant cells together. This feeding produces white, dark or translucent spots 1/16 to 1/8 inch in diameter on the plant's leaves, which can merge together (if there is substantial damage) forming large blotches. Entire leaves can turn brown, curl up and eventually fall off. If feeding occurs on new growth, wilting may result. The damage by four-lined plant bugs may be misidentified as fungal disease spots because of their similar appearance. When the damaged portion of the leaf falls out, a shot hole will remain that looks similar to fungal disease. Four-lined plant bugs can be troublesome to get rid of. During the fall, the banana-shaped eggs are laid in the old stems of the plant. The eggs will overwinter and hatch in late April-May just after the plant's foliage emerge. The agility of this bug contributes to the problem because when disturbed, the bug will drop to the ground or will hide and is therefore rarely seen. In order to keep damage to a minimum, begin to check plants in midspring around May-June for damage. Start to use control at the first sign of damage, since just a few bugs can cause severe damage. Insecticidal soaps and summer horticultural oils prove useful as well as acephate or malathion. It is also possible to remove a lot of the old stem in the fall, which will likely remove egg masses. Look for the eggs; they are banana-shaped and highly visible and can be easily disposed of when there are no leaves on the plant. The best way to beat a lot of damage is to be observant early on in the year because once you start to see signs of damage, you have to act quickly. Four-lined plant bugs have only one life cycle per season. The damage will usually stop sometime around the end of June, so spraying later than June for this insect is not usually necessary or effective." Spock Here is a link that might be useful: Ask Dan, The Herald in Orange County, CA