Popular Science Monthly/Volume 81/November 1912/Modern Warfare Against Grasshoppers
|MODERN WARFARE AGAINST GRASSHOPPERS|
MINNESOTA EXPERIMENT STATION, STATE UNIVERSITY, MINNEAPOLIS
IN all probability there will never be in the middle west a repetition of such uneasiness and alarm as prevailed during the early seventies in the states of the upper Mississippi and Missouri valleys, on account of the so-called Rocky Mountain grasshopper, Melanoplus (Caloptenus) spretus. Entomologists living in the area bounded by the Rockies on the west and the Mississippi Valley on the east report that for many years they have been unable to collect a baker's dozen of this long-winged locust east of the western plains, which represent occasional breeding grounds of this at one time destructive species, or in the foothills of the Rockies, believed to be the source and permanent breeding grounds of the pest, although it is reported that a few individuals have recently been captured in the Rocky Mountain districts. The passing of this insect may be in slight part due to the settling up of much of the country formerly utilized by them as breeding grounds, either temporarily or permanently. But so suddenly has it disappeared, and so markedly has been the increase of an allied shorter-winged form, M. atlanis (the lesser migratory locust), closely resembling M. spretus, that a suspicion exists that the latter may have been a varietal and, we may say, a sporadic form of the first named. Farmers, however, and others in the region indicated, must rid themselves of the idea that the winged visitor from the Rockies which, years ago, laid waste their fields, is the one grasshopper to be dreaded. Indeed, they are beginning to realize that in the rapid increase of some of our common species, which we may refer to as "native" species, there exists a serious menace to successful farming. Any grasshopper or locust is injurious in proportion to its abundance, and during the last three years a marked increase of a few of our common forms, and the accompanying and yearly increasing injury to crops, constitute a "writing on the wall," as it were, well calculated to rouse citizens from a feeling of absolute security to an appreciation of the need of practical measures of control. This menace is of interest not only to farmers, but naturally also to business men in any community so afflicted, since the business prosperity of a locality depends very largely on the prosperity of the farmers.
The farmer living in a neighborhood under complete cultivation, containing but a small amount of unfilled land, has little to fear, but
|Fig. 1. Two-striped Locust or Grasshopper (Melanoplus bivittatus), Female.||Fig. 2. Two-striped Locust or Grasshopper, Young Form. Representing stage best adapted to be killed by poisonous spray.|
|Fig. 3. Lesser Migratory Locust or Grasshopper (M. atlantis), Male.||Fig. 4. Differential Locust or Grasshopper (M. differentialis), Male.|
|Fig. 5. Pellucid Locust or Grasshopper (Camnula pellucida), Male.||Fig. 6. The Red-legged Locust or Grasshopper (M. femur-rubum).|
does get some relief by the constant use of the old-time "hopper dozer," driving it back and forth over his fields while the grain is young. He may, if there is no hay crop at stake, and at some considerable risk to fences and buildings, burn over fields where myriads of young hoppers are a few days old, if such fields are burnable; and he may successfully, and with considerable profit to himself and family, protect his vegetable garden with a flock of grasshopper devouring turkeys. Yet none of the above measures is sufficient to obtain the results necessary to successfully meet existing conditions, none of them makes a sufficient impression upon the hordes of grain-devouring insects. The exigencies of the case prompted the writer to experiment with a poison spray (arsenite of soda) found successful in South Africa. Our legislature of 1910-11, influenced by the fact that these pests were on the increase, and that in 1910 the state lost almost or quite two thirds of its flax crop through the work of grasshoppers, granted a small appropriation for two years' work against this insect, under the direction of the state entomologist. With these funds available, we were enabled to employ four specialists in the field during the summer, to buy spraying outfits and spraying material, and to visit and personally help individual farmers asking aid.
The mental attitude of many of these citizens toward this work is interesting. In the first place, in the winter, an apathetic condition prevails; the lesser losses are forgotten, "Hope springs eternal," etc., but in the summer, too late for efficient work, our office is deluged with mail from the same farmers who, in the late fall and winter, expressed doubts as to the recurrence of the trouble. And then, too, we have the more or less shiftless renter who says, "No, I do not think I will do anything—hardly worth while—I move next year." We find, too, a certain class, foreigners mostly (a large portion of Minnesota farmers are Scandinavians), who feel that the state should send men to their fields at its own expense, protect their crops by the state's efforts, and, incredible as it may seem, in some instances, pay them (the farmers) 8 generous board bill at the same time. Then, too, many of the real estate men in a locality more or less afflicted, look with disfavor upon efforts naturally attended with some publicity, to instruct the farmers in methods of control, claiming it injures business.
The misconceptions regarding grasshoppers and locusts which prevail, and the consequent errors which creep into print, are amazing, the most common one possibly being confounding of one of the harvest flies, or so-called seventeen-year locust, with the true locust or grasshoppers. The seventeen-year locust or periodical cicada, which, by the way, is as yet lacking, or extremely rare in Minnesota, is a sucking insect and belongs to an entirely different order than that of locusts or grasshoppers. One can imagine, then, the feelings of an entomologist upon beholding the following newspaper comment, placed upon the front page with startling head-lines: "Within the past week several farmers have seen the genuine red-legged, seventeen-year, or Rocky Mountain locust flying high in the air." We have used the term "grasshopper" repeatedly in this article, because it is a popular
term for these insects, but scientifically erroneous, for the species particularly injurious, in that they are the most numerous, belong to the family Acrididæ, while the true grasshoppers, having long antennae, and ordinarily more or less sharply pointed heads, belong to the family Locustidæ. The common error of calling the periodical cicada and other species of cicada "locusts" adds to the popular confusion. Of the injurious Acridids found in Minnesota only four species are sufficiently numerous to warrant our classifying them at this time as a serious menace to crop growing, namely, the lesser migratory locust, Melanoplus atlanis; the two-striped locust, Melanoplus bivitattus; the
red-legged locust, M. femur-rubrum; the differential locust, M. differentialis, to which we may add, possibly, the pellucid locust, Camnula pellucida, and the short-winged locust, Stenobothris curtipennis. All of these yielded to a poison spray made by dissolving three pounds of arsenite of soda in 180 gallons of water, and adding to this solution one and one half gallons of cheap molasses. This is essentially the South African formula, though in spraying the veldt a much stronger solution was used in Africa, so strong, in fact, that vegetation was killed, a fact of little import under the conditions in the African campaign, but of the utmost importance where, as in the middle west, pastures or even grain fields have to be treated. We found that at the strength used by us no appreciable injury was evident, and although it took from 24 to 36 hours for the insects to die after partaking of the poison, a partial paralysis was the result, and no food was taken by the afflicted animal after his poisoned meal. We applied this by means of large field sprayers, the spray covering 23 lineal feet of ground at once, though the ordinary potato sprayers could also be used. Generally speaking about fifty gallons will cover an acre, and the cost per acre, exclusive of labor, is about 30c. This figure would, of course, be influenced to a greater or less extent by the location of the water supply. A tank wagon in the field would naturally lessen waste of time in this connection. The question as to the effect of this poisoned forage upon stock naturally presents itself at this point, and we have reason to say
that, as used by us, there appears to be no danger from this source. Of course, unrestricted feeding upon grass drenched with a poison spray on the part of animals, forced to use such feed, and allowed no other forage, might, and probably would, have bad results, but in ordinary practice, as applied in a grasshopper campaign in North America, such conditions would not present themselves, albeit the farmer must bear in mind that he is handling an internal poison, cumulative in effect, the partaking of which in large quantities would probably mean death to any animal.
To be more explicit, the above opinion is based upon several experiments we have tried personally at the Minnesota Experiment Station, the following, and last, constituting sufficient proof to warrant the statement. A yearling heifer was placed in an enclosed plot containing 1 of an acre, after the grass thereon had been poisoned with the arsenate of soda spray (strength given above) at the rate of sixty gallons per acre. The animal cropped freely upon this without any ill effect. This poisoning of the grass was repeated twice thereafter, and after allowing her to remain several days in the inclosure after the third spraying, she was removed, to all appearances in even better condition than at the beginning of the experiment.
It is only from an actual test like this that one is justified in making
a statement and even in this case we qualify it by reminding the farmer that carelessness with the mixture might cause a fatal accident. Nevertheless it is evident that, properly used as directed against grasshoppers, no such severe tests as above would arise.
Many will remember a legal case in a western state where a smelting company was sued by a stock owner on the ground that the latter's pasturage was poisoned by arsenic coming from the smelters and the consequent death of the stock. The interesting point of this suit was the fact that the loss did not occur until after several months' feeding on the grass claimed to be poisoned.
An obstacle met with by the farmers in a practical application of this method is the difficulty they experience in obtaining arsenate of soda in sufficient quantity, and at reasonable cost, from the country druggist at the time when it is most needed. The most effective time to spray, and also the most economical, is shortly after the "hoppers" hatch, and long before they obtain wings, and the average farmer is not far-sighted enough to lay in a supply of the poison before hand. It is to be hoped that this difficulty, the chief obstacle in connection with spraying, will be overcome.
While advising spraying, we do not lose sight of the older methods, more or less effective, that entomologists have been urging upon farmers in years past: the old time "hopper-dozer" with kerosene in the pan, late fall plowing, a flock of turkeys to protect the garden, etc. Our work, however, has resulted in throwing doubt upon the effectiveness of some of the generally accepted methods and has made it necessary to qualify statements made in all good faith from time immemorial. For example, the entomologist, when the farmer has declared that a large number of grasshoppers jump out of the hopper-dozer and are not killed, assuming an air of wisdom, has said, "No, if they only touch the kerosene they are bound to die, even if they appear to have escaped destruction at the time." Last summer's work has made it evident that this is only true of the short-winged forms, in which the oil can reach the spiracles; in others, where the wings cover these breathing openings and protect them as well as the body of the insect, they live to carry on the work of destruction. Again, farmers living in grasshopper-infested regions generally handle so much land that late fall plowing is impossible. As a rule, they begin to plow, in the latitude of Minnesota at least, in August, as soon as the crop is off the ground and the grasshoppers find no better place to deposit their eggs than in the plowed stubble.
Further, this advice is based largely upon the theory that if the "pocket" or capsule containing the eggs is turned upside down, or nearly so, the newly hatched hopper never gets out and perishes. It appears, however, that this view, accepted as a truth by each succeeding generation of entomologists, must be modified, for it is probable that the capsule, becoming soft and gelatinous by the action of the elements, or perhaps disappearing altogether by May, offers no obstacle to the imprisoned insect, and still further, we have no positive proof that the newly-hatched hopper can not ascend through many inches of the soil until the surface is reached. Laboratory experiments during the summer of 1912 indicate that the newly-hatched grasshopper may work his way through eight inches of fairly well packed soil.
Finally, it has been commonly believed, and is doubtless true of the majority of insects, that alternate freezing and thawing is fatal. But one of the field men exposed last winter about twenty young hoppers, hatched in the warmth of indoors, to alternately a freezing and thawing temperature several times, with no bad results to the insects, one only succumbing and that probably being injured in handling. These observations appear to leave open a large field for investigation along the lines of grasshopper control.
Grasshoppers have many enemies, but their numbers are so enormous that the latter cause but little apparent depletion in their ranks. Many of our song birds eat them, as well as black-birds and crows. The sparrow-hawk's crop is filled with them in the fall, and at least one variety of tern helps the farmer materially in this direction. Skunks and other predatory mammals are partial to them, and we have per- sonally observed the thirteen-lined gopher (Sphermophilus tridecem- lineatus) catching and devouring them in the cool mornings of autumn. Among insect enemies, parasitic and predaceous flies are very useful in their attack upon the eggs as well as upon the hoppers themselves. Various beetles, notably some of the meloids or "Blister Beetles," insects which are themselves destructive to crops in the adult stage, make some amends for their destructiveness by preying upon the eggs.
Farmers, seeing small mites fastened to the wings and bodies of grasshoppers, have been wont to comfort themselves with the thought that these animals were reducing the number of the pests. Inasmuch as we have seen female hoppers in the fall, laden with these possible parasites, laying eggs for the next generation, having themselves com- pleted their destructive life history, we believe too much reliance has been placed upon this phenomenon in the past and are inclined to regard their occurrence on grasshoppers as a means of dispersal of the species of mite in question, rather than a serious drain upon the vitality of the grasshopper.
It would seem, then, that the farmer must rely principally upon his own effort in this warfare, unless forsooth nature favors him by sending many cold drenching rains in May and June when the hoppers are hatching, which not only result in great mortality amongst the insects themselves, but give the crops such a stimulus that they are better enabled to withstand the inroad of these pests.