The 2018 season will forever be etched in my memory for its epic hatch of Japanese Beetles. Hundreds of thousands of them. I sprayed every week to kill them off. By the next week, a whole new generation had emerged from the soil and moved into the vineyard.
I got quite familiar with certain vines that seemed to be of lesser interest to the beetles. There were some obvious ones, like ES 6-16-30 and T.P. 2-3-51, that the beetles were not attracted to because of their tough, corrugated leaves. But there were a few vines in the seedling blocks with thinner, uncorregated leaves that also seemed somewhat unattractive to the beetles compared to their neighbor seedlings.
One way to test the relative unattractiveness of these seedling vines was to set up a forced choice feeding environment for the beetles. I put a fixed number of beetles into a fine mesh containment bag that contained one growing shoot from a highly attractive seedling vine and one growing shoot from a neighboring, relatively unattractive vine. If the beetles wanted to eat, they could choose either seedling or both.
At the end of the trial, each of the leaves in the study was photographed for later analysis of leaf damage. I have not had time to finish the analysis of the photos, but hope to get to it this winter.
There may be some genetic basis for the unattractiveness. All four of the seedlings that showed some level of unattractiveness to Japanese Beetles are from the same cross and, genetically, one-fourth Vitis palmata. My vine of Vitis palmata grows outdoors during the summer in a big pot. The beetles do not bother it, even though it is surrounded by potted vinifera vines which are highly attractive to them.