It may be, however, that some of the chestnuts carry immunity factors. In the U. S. Department of Agriculture Circular No. 547, published in 1940, "Feeding Habits of the Japanese Beetle," by I. M. Hawley and F. W. Metzger, ~Castanea crenata~, the Japanese chestnut, is listed with beech and chestnut oak as "generally lightly injured." I understand you consider the nut of this species poor, but if resistance factors are in the genus, there can be hope of finding or developing a chestnut resistant to Japanese beetle.
We might be able to do with chestnuts what has been done with poplars. The common poplars range from the Lombardy, ~Populus nigra italica~, which is heavily damaged by the beetle, to the white, ~P. alba~, which is immune. The forest geneticist, E. J. Schreiner, has written an article, "Poplars can be bred to order," which appears on pages 153 to 157 in "Trees," the Yearbook of Agriculture for 1949, published by the U. S. Department of Agriculture. Schreiner provides an interesting 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 attacked than a large one set in a clearing in the woods.
~Control of the adult:~ The safest, most direct measure is to pick or knock the beetles off the plants, preferably in the early morning, when they are cool. They may be dropped in a pail with a little kerosene in it. Some plants can be shielded with thin nets which can be placed on them by day. We do not recommend Japanese beetle traps. These yellow traps, which are baited with geranoil and other essential oils, can draw beetles in from a considerable distance but we have found that, possibly because many beetles miss the trap, the population of beetles remains high near the trap, in spite of heavy daily catches. Although the use of one trap to the acre on a block 10 miles square would probably get results, the use of a few traps on a small nut planting is likely to be disappointing.
A MEMBER: Will birds or any kind of poultry eat them?
DR. ADAMS: Yes, poultry will eat them, as far as they can reach. Certain birds, of course, will feed on them to some extent, but birds, in summer, seem to have plenty of other things to eat, and they certainly leave plenty of beetles in plain sight uneaten. We can see that the birds are a fairly constant helpful factor, but are not to be relied upon to prevent injury occurring in a beetle outbreak.
Rotenone, which, I believe, is one of your main insecticides in nut culture, is fairly effective on Japanese beetles. It kills the beetles hit with the spray and gives protection for several days thereafter. If you apply it often enough, rotenone can take care of the plants so that they don't become disfigured by the beetles. Using cube powder, you may apply five ounces of 4% rotenone in 10 gallons of water. Of course, in many cases there is no objection to using DDT wetable powder or dusts, unless you are afraid of a mite problem arising after DDT is used. If DDT can be sprayed on the plants, it needs to be applied only about three times during a summer, or sometimes only twice. For plants that are growing very fast, the new growth, of course, has to be kept treated. You may prefer to spray once heavily over all the plants in July and then, after that, keep the beetles off by spraying or dusting the new growth, during August. For more directions see U.S.D.A. Farmers Bulletin No. 2004.
Now, there are new chemicals that will kill Japanese beetles very quickly. Parathion will kill them, but its toxicity necessitates great care in handling and, on peaches, we find it protects the plants for only a few days. Chlordane, which has a very important use in connection with these insects in the grub stage, is not recommended above ground; it is too brief in its action. Methoxychlor may be used instead of DDT. It is less effective, but much less poisonous, and should be applied more frequently.
Now, the other aspect of control is to try to reduce beetle production over the whole area so that you don't have so many beetles flying in to the plants during the summer and you don't have to spray so frequently, if at all. This is the phase to which I wish to give particular attention, after we consider the life history.