Focus on the mouthparts... This is the specimen at left in the above picture, seen at 10X higher magnification, and rotated for better crossed-eye stereo.
I did not know what these things were, when I first saw them on the leaves of my grape vine.
Some amount of photography and searching later, I now understand that these are Virginia Creeper Leafhoppers (Erythroneura ziczac). They are native to the central U.S., but have recently (last 10 years) spread to the west coast, where they are becoming a problem for both home garden and commercial grape growers.
There are two main concerns with these beasts. The first is that the adults and all nymphal stages feed voraciously by penetrating leaf cells with their exquisitely sharp mouthparts and sucking out or destroying the cell contents. If this damage is limited to 20% or less of the leaf area, then the plants can probably develop and bear normally. However, the leafhoppers reproduce quickly, two or more broods per year, and if the egg parasite wasps cannot keep up with them, the overall population can rapidly exceed the damage threshold. The second problem is that these leafhoppers have been shown in greenhouse studies to be capable of serving as vector for a plant virus, Red Blotch Disease, that seriously messes up the crop. The net effect, according to one of the sources I ran into, is that commercial practice may have to shift from threshold-based tolerance to eradication. It remains to be seen how all that will shake out.
Here is how they look in life. Notice the small cigar-shaped lumps on the leaf, left of the leafhopper. Those are eggs, laid between the leaf layers.
Finally, here is a leaf that shows the extent of the (potential) carnage to come. Yes, the cigar-shaped lumps are all eggs. Now, I'll grant that this is the most heavily infested part of this leaf, but on the other hand the leaf was chosen at random. When all these things hatch, that vine will be way over threshold. Unfortunately I found no sign of the egg-parasite wasps, just lots of apparently contented leafhoppers. Chemical treatment has begun...
Photography with Mitutoyo M Plan Apo 2X and 20X objectives in studio, MP-E 65 at 2X in field. Flash illumination in both cases: 2X Yonguo speedlights in studio, through a plastic globe diffuser; Canon 580EX II flash with softbox diffuser on positioning arm in field. Canon T1i camera (APS-C format).
--Rik
