resting diagram of
random planting of 102 poplar hybrids, in plots of 50 trees each,
representing 30 parentages. He writes, "Japanese beetle infestation was
heavy in ~1947~; as late as September 9 beetles were as numerous as 10 to
12 per leaf on the most susceptible plants. Although the insects were
feeding everywhere on the sparsely scattered weeds growing under the
hybrids, beetle feeding was found on only nine hybrids, representing
four parentages. Three of these parentages include hybrids that were
entirely free of beetle feeding during the entire infestation." Among
five hybrids of ~P. charkowiensis~ and ~P. caudina~, three were highly
susceptible, one moderately susceptible and one was non-susceptible.

Japanese beetles, when infesting rows of plants of the same variety,
usually occur unevenly on the individual plants. Some of the factors
have to do with the vigor or color of the tree. In my observation on
peach, I have repeatedly seen a sickly, yellow and half-wilted tree with
thousands of beetles in it, while other similar but healthy trees in the
same row averaged only a few hundred beetles. You can make one branch of
a tree more attractive to the insects than the rest of the branches by
partly girdling it or permitting borers or cankers to damage the base of
the branch. This observation suggests that the increased sugar content
raises the attractiveness of the leaf. It coincides with what is already
known that extracts of plants preferred by the Japanese beetle have, in
general, a higher sugar content, or more of a fruit-like odor than those
not attacked. (Metzger et al, Jour. Agric. Research, ~49~ (11): 1001-1008.
1934. Washington, D. C.)

There are other observations you can easily make yourselves. The
Japanese beetle avoids shade, except on the hottest days, and its
feeding in dense trees shows up most in the tops; its feeding on uniform
plantings tends to show up most in the edge rows. Nursery-size trees are
more extensively defoliated than larger ones. At this point we must
consider that the insect usually has to fly into a planting from the
outside, for it breeds chiefly in lawns and meadows. If the foliage mass
of the nut planting is small and the grass areas nearby are large, the
beetles are likely to do heavier damage than where the planting is very
large and grass areas negligible. A small planting in a suburban area,
beside a large golf course, cemetery or dairy farm, is going to be more
heavily at