The Japanese Beetle

Date Published: 
August, 1923
Original Author: 
C. H. Hadley
Original Publication: 
AACS Proceedings of the 37th Annual Convention

Ladies and gentlemen, I feel that I owe you a little bit of apology in appearing here with what comparatively little I have to show you. I had expected to show slides, which I always figure save me a lot of work because what the slides show I do not have to tell you, but unfortunately for me, at least, my slides apparently were lost on the way and have not shown up and in the very short time allowed me for tracing the slides and finding other illustrated material to show you I was unable to find very much. At this season of the year most of the material of this type is out on the road at fairs and other similar places. However, I will try to make up for the lack of actual material by explaining as we go along.

You are particularly interested, I assume, in the question of the relation of this insect to industry which you people are representing, and I will try to confine my general remarks to that particular phase of the proposition. Before going much further I just want to pass around two mounts, one on each side, which show the insect itself in the various stages and two small samples of leaves showing the general way in which it attacks the foliage.

Now a little about this insect and how it got here, and so forth. As you surmise from the name of the insect "Japanese Beetle", it is a native of the islands of Japan and of a certain few nearby islands in that part of the world. So far as we know the insect arrived in this country prior to 1916, and probably somewhere around 1910 to 1912, as a grub or soft grub about the roots of Japanese plants probably the Iris or Azalea or a similar variety, the roots of which come in the soil. It was first found in New Jersey in the vicinity of Riverton which is about nine miles above Camden, on the Jersey shore of the Delaware River in the summer of 1916. At the time two inspectors of the New Jersey Department of Agriculture found it, not knowing what it was, but merely recognizing that it was something new to them and not a habitat found in this part of the country as far as they knew, and after a. little searching around there, being enthusiastic collectors as well as official inspectors, they tried to find as many individuals as they could to work with it. They found in the neighborhood of a dozen or so within a quarter mile radius of this same field. It happened to be along the edge of a little creek running through there where they found them. Four years after that, in 1920, one man collected in about two hours' time six quarts of the beetles. Now there are relatively 3500 beetles in a pint or 7000 in a quart so you can judge from that something of the increase in numbers of the insect since that time. The insect has spread annually, as we believe, at a definite rate from the original point of infestation, at the rate of five to ten miles per year in all directions. That we believe to be the normal actual spread of the insect in new environment. The map I have here which I will open up (does so); shows color variations which indicate the gradual spread of the insect from the original point of infestation. You will notice the different colors represent the spread year by year from the original point of infestation, which point is in the centre of the map here, and a scale of the map is an inch to a mile. You can get a good idea from that as to the rate of spread. This is the City of Philadelphia here (indicating) the Delaware River running up to Trenton, up here towards New York; this being Riverton right up here, and the original point of infestation about three miles out from the town. That represents, as well as we have any example, the comparatively steady spread of an insect in a new locality, steady and uniform, and we do not expect to be able to prevent that yearly spread, the actual spread of the insect. At the present time the infested area, or rather up to the beginning of the present season. the middle of June, the infested area covered 770 square miles, the increase being from less than one-half a square mile in 1916. So far as is known the insect does not occur any place in the world other than this infested area in New Jersey and Pennsylvania and its original home country in and near the islands of Japan; and one phase of our work, namely, quarantine enforcement is aimed to prevent as far as possible the widespread distribution of this insect.

Now a little as to the life history; you are more or less acquainted with a class of insects closely related to this Japanese Beetle, that is, the May beetles or June beetles, as they are commonly called. This Japanese insect belongs to the same general family of Mayor June beetles. If we start at the present season for instance to trace the life history throughout the year just now we are in the tail end of the beetle season. At the present time the progeny of the present beetle generation, the eggs and grub which have hatched from that, is in the ground feeding. They will remain here all winter and until next spring as a grub, increasing in size, at least increasing up to real cold weather and then hibernating for the winter and recommencing growth in the spring up until we will say about the middle of May. Then there is a transformation, still under the ground, to what we know as the pupa stage. For instance, you are acquainted with the June beetle caterpillar, the beetle in the intermediate stage that is the cocoon, it is the intermediate stage. This stage lasts apparently about two weeks. The earliest beetles commence hatching between the 10th and 15th of June. Throughout the rest of the summer then there is a continuous hatching of the beetles. But the height of the season is from the latter part of June through July and early August that completes the life history for the year. There is but one generation per year so far as we know. A single female beetle will lay on an average of 30 to 60 eggs during her laying period which extends practically through the season of the beetle flight from the latter part of June until early August.

Now, to give you an idea of the ability of this species to carry itself through and to show how it withstands adverse conditions.  It does not breed as rapidly as some other insects but it has practically 100 percent of young that come through to maturity. To illustrate that point I will cite this one example. Two or three years back we were interested in finding out how many eggs would hatch and mature, so for a number of days we collected 100 eggs a day for a period of three weeks, taking them from different places in the soil and we averaged 99 or slightly better than that in the average of each 100 eggs hatched and the grub surviving. In another test we collected 1200 eggs in one day from a number of points, brought them into the laboratory, each egg was put in a small tin an inch in diameter, in soil and kept to determine the hatching, and we were able to hatch out exactly 1200 larvae from the 1200 eggs. In other words, the insect in all stages is very resistant to adverse conditions, which explains why we have such an increase in the comparatively few years it has been here.

Now a little bit about the habits of the insect: The more injurious stage is the parent beetles. We have records of their feeding on something over 200 different species of plants. I think it is about 220 including useful and cultivated varieties as well as non-useful weed varieties. There are certain different preferences they make. They show a preference for certain weeds such as smart weed, alder and mallow.  Unfortunately, however, their preference is not strong enough to allow them or to keep them feeding on the weed varieties only and there seems to be a notable tendency, as the insect becomes better established, to leave the weed varieties for the cultivated varieties. There is only one cultivated class, ornamental, that is distinctly free of attack from the insect and that is the conifer group, arbor vitae, pines, hemlocks, all that class. We have no record of their feeding on that class of plants. Now, from your standpoint it is quite possible that the grub, or young form, will be equally, if not more seriously destructive because of the fact that they feed on the roots of plants, particularly grass. Now, they are comparatively a small grub and a few grubs in the sod we will say don't make any appreciable difference. I mean by that 100 to 150 per square yard. It sounds quite a few but from our angle it is not. Now they begin to be real serious when they run up to three to five hundred grubs to the square yard. Under these conditions you can and will get serious injury to the sod, particularly in the fall, and especially if that is followed by a hard winter there will be a good deal of dying out of the sod. Now, when they get what we call real dense, that is, over 500 to the square yard, then you are pretty sure to get serious injury. To give you an idea of how high they may go, a year ago this fall the highest infestation we found was 1035 grub in a measured square yard in the golf course at Riverton. That is a good many grubs. That figure is not simply based on one examination but an average of several in the most heavily infested places. We thought that was about the limit that could be reached but an examination already this fall, just beginning there, seems to promise a figure running up close to 1500. You can realize that that degree of infestation may be called a heavy infestation and undoubtedly will give lots of trouble.

Now, a little about the work we are doing at Riverton because we all have run into at least the quarantine phase of it at one time or another; if you have not, you will, especially in the purchase of nursery stock from this part of the country. The work is divided into certain main phases: For instance, part has to do with the study of the life history, the habits of the insect in, the new environment, the changes from year to year as it becomes better acclimated, and so forth. Another line has to do with the importation and distribution of parasites which we hope will eventually hold the insect in reasonable check. In Japan the insect is not of any economical importance itself. They have occasional outbreaks where it does some damage and they collect a lot by hand and destroy them; but I suppose in 100 years there has not been the amount of injury occasioned in Japan that there has been in the last two years in the heavily infested areas of New Jersey and Pennsylvania. There are two reasons for the apparent non-importance of the insect in Japan. One is the cultural practices of the country. There is practically no waste land; everything is intensively cultivated, so that the opportunities for the insect to breed in large numbers are very limited. The breeding places chosen are grass fields, pastures and waste lands in general, and, of course, around this part of the country there are plenty of them. The other reason for the lack of serious injury in Japan is the presence of native natural enemies of the insect; in other words, there are insects which prey upon it, which we commonly call parasites. These parasites we know to be present there in reasonable abundance. We have now three or four men in that part of the world who are studying the situation and sending us parasites as fast as they have material available. The parasite material is shipped to us and it is taken care of at the laboratory. Some times it comes at the time of year and at the stage where the parasites can be released immediately in the infested area. Other shipments come in such a way that the material must be carried over during the winter or at least during a season before the conditions are right for the material to be released. The ultimate object of holding this insect down to a point where it can no longer be a serious pest lies in the shipment of a sufficient sequence of parasite enemies to keep the number of the host down to a reasonable small limit. Eventually possibly certain of the native parasites existing here, the normal beetle related species to the Japanese beetle will also attack the Japanese beetle. But the main reliance must be placed upon the known natural enemies which must be brought over. Now, it will take quite a few years before the parasites can be brought to the point where they are practically proficient in keeping this pest under reasonable control. As to removing from the class of dangerous insects, we do not stress that point very much; it may be ten to fifty years; and nobody is in position to give an estimate. Meanwhile the insect is increasing and spreading and is causing damage and is going to do more. Therefore, other important phases of our work have to do with the development of methods to control the pest, not only from the standpoint of the destruction of the parent beetle itself but also for the destruction of the grubs in the soil.

The insect or beetle is quite resistant to the ordinary poisons such as arsenate of lead, Paris green, etc., that are commonly employed, or at least they are wise enough to know enough to let them alone. It is an open question as yet even whether beetles simply won't feed very much on arsenate of lead, for instance, or whether they will eat just enough arid know when it is well to stop. The fact remains that arsenate of lead, as a common insecticide, we have not yet been able to say will kill a large number of the beetles. It does give a certain amount of relief, but not many eases are very satisfactory in the prevention of injury to the foliage by simply driving the beetles from the sprayed trees to places where the spray is not present. That is a sort of backhanded way of getting at it and of course, if carried on continuously will, eventually devolve on the proposition of driving them from one place to another. We are working on that angle seeking to find a material which will kill a bulk of the insects which feed upon it, which is, safe to use on the foliage without resulting injury to the foliage and with which the cost of using is not excessive. From the standpoint of grub destruction we are also carrying on considerable work. It is possible to destroy the grub by using the sodium cyanide solution and spraying it or applying it to the infested soil. It will kill 90 to 95 percent of the grubs in the soil in the early fall while they are close to the surface. The drawback is the cost. The material runs from $60 to $75 per acre, not counting the cost of labor and the fact that special equipment is necessary to apply it. I believe that most of us will agree that the cost is excessive and certainly it is from the standpoint of the average farm land. We are concerned, therefore, in finding a cheaper method of treatment and we believe we have found a satisfactory material in a carbon disulphide emulsion which will be satisfactory at least the two years of experimental work dealing with this material have given very satisfactory results.

Another phase of the work is the quarantine. As I mentioned in the first place, we do not expect to be able to prevent the normal yearly spread of the insect, averaging between five and ten miles a year; in fact, if we had nothing but that to consider we would not have much to consider because it would take many years to go a long distance. But when we consider the fact that the insects can be spread in one year or even less, the actual spread will occur in one week through the shipment of infected nursery stock from one side of the country to the other and you realize why it is we lay so much stress upon the quarantine, a quarantine that simply restricts and controls the movement of nursery stock to places outside, does not absolutely prohibit but allows the movement only under conditions which will not spread the insect; in other words, shipments of the type which will not carry the insect are allowed, other shipments are not.
Now, as the time is going on, it is getting a little late, I do not want to take up any more time unless you have specific questions. I will call your attention, if interested, to the circular which has been issued or printed describing the insect, its habits, etc., of which I do not have a supply with me, but if you are interested you can get copies by simply writing us for them. This is a small circular describing the insect, its habits, and giving a colored enlargement of the beetle itself, and can be secured by addressing the Japanese Beetle Laboratory at Riverton, New Jersey, or the Department of Agriculture here at Harrisburg. Now we have gone over this rather briefly and hastily. If any of you have questions I will be very glad to answer them, if possible.

From the publication:
AACS - Proceedings of the 37th Annual Convention
Harrisburg, PA
August 20, 21, 22 and 23, 1923