1942: Entomology

Samson R. Dutky of Moorestown, N. J., has described two micro-organisms, Bacillus popilliae and Bacillus lentimorbus which are found in the blood of larvae beetles having milky disease. A plentiful supply of these bacteria can be obtained and possibly used against future invasions of the Japanese beetle by separating the spores from dried blood and reinjecting them into healthy larvae and thus maintaining a constant increasing supply.

Dr. A. A. Nikitin, of the Tennessee Copper Company, has reported a method whereby many kinds of enemy insects can be exterminated with dusts containing talc or fine clay which is obtained from the soil in Georgia and other southeastern states. This material, he reports, can be combined with poisonous chemicals and hence reduces the cost. Even without the addition of poisonous compounds the white dust is reported to repel many kinds of insect pests.

Dr. J. C. Cross of Texas College of Arts and Industries, Kingsville, Tex., has reported a very simple method of controlling termites. He has used his own home for the experiment and has poured discarded lubricating oil into little ditches which surround the concrete piers in the foundation. He states that the oil stays in the ground for a considerable time and does not diffuse more than a few inches from the ditches. Hence the growth of shrubs six inches distant are not affected by the oil.

A new insecticide known as Thanite and derived from Southern pine has been found to be a suitable substitute for pyrethrum and rotenone in fly-killing sprays for use in homes and dairy barns. This substance is said to be effective against mosquitoes, moths, spiders, ants, mites, bedbugs and roaches. This chemical substance, known as the thiocyanoacetate of a secondary terpene alcohol was discovered by chemists of the Hercules Powder Company and bids fair promise of further increasing American independence of war-pinched imports.

Dr. J. W. Zukel of the Department of Zoology and Entomology at Iowa State College has investigated the effect of an organic compound, known as phenothiazine, upon the American cockroach. It was found that this substance was toxic to the roach by acting entirely by contact with the body surface. No toxic effects resulted when the chemical was taken into the alimentary canal.

Investigators at the University of New Hampshire report the discovery of a new fumigant for grain and flour. It is highly penetrating and extremely deadly to insects but harmless to humans. It is known as chlorinated nitro-ethane. The chemical is a clear liquid and evaporates readily upon exposure to air. The fumes penetrate rapidly into large masses of flour or grain, hence the simple method of merely placing the chemical on top of the grain in a closed car could readily be utilized for practical purposes.

Entomologists of the U. S. Department of Agriculture report on the number of insect enemies of the guayule plant which it is hoped can be utilized in relieving the rubber shortage in this country. They have found that the most destructive insect is the bark beetle which attacks the plant after harvesting. To date this beetle is only reported in Mexico but may eventually serve as a menace in the United States at a later date unless controlled. Other potential insect enemies of the guayule plant which are being studied are the root-eating white grubs, caterpillars, grasshoppers, mites, leafhoppers, and wireworms.

Investigators at Iowa State College have made a study of the life histories and reproduction habits of the American cockroach, and have shown experimentally that a female roach may raise on the average as many as one hundred sixty-three offspring during an adult lifetime of less than one year. It was also found that in some cases reproduction could occur in unmated females while in other cases some individuals continued to reproduce offspring from several months to a year following a single mating.

Dr. W. A. Dreyer of the University of Cincinnati has made some interesting studies on the life span of the common ant-hills as found in Northern Illinois. He reports the average life span for such a community is from fifteen to twenty years with definite cycles during this period when they grow, flourish, decline, and finally die.

Dr. S. D. Griffitts, of the School of Tropical Medicine at San Juan, Puerto Rico, reports that experiments have shown that ants, usually considered harmless insects, may be guilty of spreading dysentery. Dr. Griffitts has shown by experiments that ants could carry dysentery germs on their feet at least twenty-four hours after walking across material containing the germs.

The puss caterpillar, known technically as Megalopyge opercularis has been reported guilty of poisoning individuals. Dr. T. L. Lucas, of the Walter Reed General Hospital, Washington, D. C., has reported a case in a recent issue of a medical journal. The author believes other cases no doubt occur frequently but are not reported for some reason. The poison was reported serious but not fatal. This puss caterpillar is widely distributed in the Southeastern United States, and is found on elm, plum, sycamore, and oak trees as well as in orchards and on corn.

Dr. A. B. Sabin and Robert Ward of the Children's Hospital Research Foundation and the Department of Pediatrics of the University of Cincinnati College of Medicine have continued and expanded their experiments to show the possible role of insects in the epidemiology of poliomyelitis. They have distinctly shown that flies of a number of species are carriers of the virus. However, as they state, the search for a reservoir of poliomyelitis virus among lower animals should still be continued.

1941: Entomology

Drs. J. B. Reeside, Jr., and C. E. Dobbin, of the United States Geological Survey have found the comb of a wasp nest in Southwestern Utah. This comb, dating from the last Cretaceous, or about 80,000,000 years ago, gives more evidence as to the early presence of wasps into the world.

More positive evidence that flies will harbor or carry the virus of poliomyelitis for several days, has accumulated during the past year through the experimental work of a group of investigators from the Schools of Medicine at Yale University and Louisiana State University.

Drs. H. S. Telford and C. Wester of the North Dakota Agricultural Experiment Station have reported finding two species of malaria-carrying mosquitoes in North Dakota. While this is the first report of these species in the state, the investigators assert that the occurrence is not surprising since these species have been known to occur in Manitoba and the states surrounding North Dakota.

Dr. H. Kalimus of University College, London, has carried out a series of experiments on the social behavior of bees. His experiments show that bees not only defend their home hives but also viciously attack strange bees in the collection of food.

Drs. J. C. Brown and J. C. Cross of Texas College of Arts and Industries have carried out a series of experiments and tests which tends to show that 'blue bugs' or fowl ticks, Argus persicus, are at least one of the probable agents for the transmission of fowl paralysis.

A species of mosquito, Deinocerites spanius, reportedly only occurring in Panama, has made its appearance on the coast near Brownsville, Texas. This species, as far as is known, is harmless to man. However, this insect probably migrated to this new environment by plane. This serves as another example of how insects, heretofore foreign to the United States, may be transported.

Preliminary reports of the use of a new chemical poison-spray, phenothiazine, show that it is lethal to the codling moth worm but harmless to the bee. However the United States Department of Agriculture is carrying on more extensive tests before its general use in apple orchards is to be recommended.

Heretofore a type of red scale insects resistant to cyanide gas has baffled scientistics who have attempted to control this citrus pest. Recently Drs. R. Craig and N. W. Hardman of the University of California have shown that the spiracles or air tubes of these insects can be kept closed for 30 minutes which makes the cyanide gas useless for the control of this species. Nevertheless, these investigators are hopeful of finding a substance which may be used in combination with cyanide gas and which will in turn aid in the eradication of this pest. Another group of investigators from the University of California Citrus Experiment Station are attempting other control methods against the red scale insect. They have imported an insect from South China which acts as a red scale predator. However, orchard tests, over a period of years, will be necessary to check the apparent successful laboratory tests.

Dr. G. F. MacLeod of the University of California College of Agriculture reported the results of some laboratory experiments on cockroaches. He has shown that infra-red rays were lethal to adult cockroaches. However, no practical method for large scale eradication has been suggested. These infra-red rays were also tried on numerous plant pests but the plants were injured as well as the insects in this latter experiment.

Drs. W. H. Tisdale and A. L. Flenner of the Du Pont pest control laboratory at Wilmington, Delaware, have described a chemical compound derived from dithiocarbamic acid, which, when used as a spray disables the Japanese beetle. This chemical has also been found effective against certain internal parasites in animals as well as certain fungi causing plant diseases.

Drs. W. N. Sullivan and L. D. Goodhue of the United States Department of Agriculture have shown how rotenone or pyrethrum, insect spray poisons, can be more effective by being used as a fumigant. To produce 'aerosols' from these substances they must be sprayed over heated appliances. The advantages offered by these substances as fumigants are that they are harmless to animal life.

A. M. Chickering of Albion College reported having separated out 21 new species of spiders from his collections of 1934, 1936 and 1939 from several localities in Panama.

Dr. I. W. Pfeiffer of Yale University has reported that castration of females of the grasshopper Melanoplus differentialis resulted in a progressive depletion in fat values well below the normal level. Furthermore, her experiments also show that when the corpora allata of these castrated insects is also removed the effects of castration are eliminated and the yielded fat and water values return to a high level.

The mechanism by which the female larvae of the honeybee are differentiated into queens and workers is assumed to be determined by food and care received during the larval period, because it is quite generally accepted that such ecological factors as temperature and relative humidity are the same during the development of both castes. In order to gain a better understanding of caste determination a particular character has been selected by Drs. G. H. Mickey and R. M. Melampy of Louisiana University. They selected the fat body of the honeybee larva and made extensive cytological studies of the cells in this structure. In general, they found that the changes which the cells undergo during larval life are the same for both the queen and worker bees. However, the changes seemed to occur earlier in the larval life of the bees which were destined to become queens. See also BIOLOGY; CHEMISTRY; ZOOLOGY.

1940: Entomology

Malaria Mosquitoes.

That malaria mosquitoes in the Tennessee Valley spend the winter in hibernation was reported by Drs. E. H. Hinman and H. S. Hurlbut of the Tennessee Valley Authority. The specimens they found in their investigations were all adult females that had mated. Hence, they were ready to lay eggs as soon as warm weather permitted. These workers also report that the hibernating females in caves have survived as long as 69 days without food with the temperature ranging from 51.5° to 59° F.

Protection of Crops by Insects.

Moth Ravages in Orchards Abated by Wasps.

Drs. J. E. Webb, Jr., and C. H. Alden of the Georgia State Department of Entomology, have presented some interesting data on how the wasp Trichogramma minutum has aided in abating the ravages of the codling moth and fruit moth in the Georgia peach and apple orchards. They state that during the past 10 years more than 300 million of these wasps have been raised and released to range the orchards. The wasp eggs are laid within the moth eggs and the wasp larvae then destroy the moth eggs. Upon collection and examination of moth eggs, it was found that more than 50 per cent had been rendered incapable of further development by the wasp larvae.

Bean Beetle Checked by Fly.

The Mexican bean beetle, now a serious crop pest in many eastern and southeastern states, will soon have a natural enemy to keep it in check in the United States just as it is checked in Central Mexico. Drs. B. J. Landis and N. F. Howard report that encouraging results have been obtained with a fly, Paradexodes epilachnae. These flies have been reared at Columbus, Ohio, for the past ten years and some 82,000 have recently been released in 19 states to aid in keeping the bean beetle in check.

Harmful Grubs Destroyed by Greenhead Ants.

Professor H. B. Fell of the University of Edinburgh has reported on studies he has made of a number of colonies of greenhead ants found in Australia. He states that the greenhead ant is of decided value to the farmer. He observed a single colony of a few hundred individuals over an eleven hour period and found them bringing in 125 larvae of beetles, moths and flies and a smaller number of various spiders, termites and red ants. Hence an estimated 45,000 harmful grubs would be destroyed by one colony of ants per year.

Physiological Researches.

Function of Corpora Allata in the Grasshopper.

Dr. I. W. Pfeiffer of Yale University has been carrying out physiological researches for the past ten years on the grasshopper, Melanoplus differentialis. She has recently reported another series of experiments on the function of corpora allata in these insects. These structures are somewhat similar in function to endocrine structures in higher forms known as corpora lutea. It was previously shown that the production of secretion by the oviducts and development of the eggs during the yolk deposition period was controlled by corpora allata, probably through a hormonal agency. Now it has been found by a series of transplantation experiments, that male corpora allata would perform the usual female function when grafted into females but when ovaries of the female were placed into males these ovaries would not develop yolk. This shows that while both males and females possess physiologically similar corpora allata the males no doubt also possess some inhibitory agent or a deficiency of some sort is present in the male which is vital to the egg during the yolk deposition period.

Insect Head Possible Additional Source of Internal Secretion.

Dr. M. F. Day of Harvard University has made a histological study of the heads of a number of species of insects and using the charactic staining reactions, on a number of structures in the heads of these insects, he suggests additional possible sources of internal secretions from the heads of some holometabolous insects.

Wound Healing in Grasshopper.

Mr. Garth Johnson of the State University of Iowa has reported a detailed description of the process of wound healing in the grasshopper. In general the process is more or less similar to that found in vertebrates except the scar tissue in these forms seems to develop from differentiated blood cells which is then followed by an activation of adjacent epidermis.

Life Tables of the Flour Beetle.

Dr. R. Pearl of Johns Hopkins University and Drs. T. Park and J. R. Miner of Chicago and the Mayo Clinic have recently reported life tables for the flour beetle Tribolium confusum Dutal while working on their experimental studies on the duration of life. Life tables were constructed for 400 male and 400 female beetles. The mean duration for males was 177.8 and for females 198.5 days. One male had a maximum life span of 540 days and one female 435 days. The interesting thing about these life tables was their close resemblance in fundamental pattern to human life curves. In fact the resemblance is closer than that of any other organism for which life tables have as yet been computed.

Cytological Experiments.

On Male Reproductive Cells in Grasshoppers.

Drs. H. W. Beams and R. L. King of the State University of Iowa have carried out some interesting cytological experiments on the male reproductive cells in the grasshopper. Mitotic spindles in the metaphase stage were partially or completely separated from the chromosomes by ultracentrifuging. Aside from the details of the experiment the important point was the additional evidence that the mitotic spindle is a body of substantial nature and was not destroyed (liquefied) by ultracentrifuging.

Cell Number and Cell Size in the Growth of Insects.

Interesting observations on the cell number and cell size in the growth of insects have been carried out by B. N. Smallman of McGill University. In general, it was found that tissues which were destined to be histolyzed during metamorphosis tended to grow by increase in size of their cells while tissues which persist to the adult stage tended to grow by an increase in cell number.

Enzymes in Insects.

Work from a number of institutions has been continued on researches concerned with the physiological and histochemical investigation of enzymes in an attempt to more precisely find the origin or source and also the action of these enzymes in insects. Most of the work along these lines has been carried out to date on the dragonfly and the grasshopper. See also BIOLOGY; ZOOLOGY.

1939: Entomology

Important researches in the field of insect embryology, genetics and physiology have continued this year. However, the outstanding entomological work for the past year seems to be more or less in the fields of ecological and economic entomology.

Wing Speed of Insects.

In previous years workers have concerned themselves with the speed of flight of a number of insects. Scientists have heretofore reported the speeds of flying insects of various species to be between 18 to 33 miles per hour. With the aid of high speed stroboscopic and photographic technique, Dr. L. E. Chadwick, of the Harvard Biological Laboratories, has made a number of interesting studies in 1939 on the speed of wing beat of various species of insects. His preliminary studies show that wing speeds vary widely. The honey bee averages between 160 and 200 wing beats per second, the bumblebee, 240, the common housefly about 160, while the fruit fly has a speed somewhat above most of the others examined. The fruit fly has a wing speed varying from about 9,000 to 13,000 per minute under normal conditions. Dr. Chadwick has also shown that the speed of the wing beat in the fruit fly increases with a rise in temperature and furthermore, that fatigue lowers the rate. However, 2,000 to 3,000 strokes are usually managed under temperatures of 84° F. When we consider the wings of a humming bird as going about 50 beats per second, we can all the more appreciate these tremendous speeds in insects.

Migration of Butterflies.

Ornithologists and ichthyologists have been marking live birds and fish for future identification in the study of ecology for a number of years, but Dr. P. H. Smyth of Montgomery, Alabama, is one of the few scientists who has tried out this new idea on butterflies in an effort to obtain more specific information about the great cloud of flights of apparently migrating butterflies. Dr. Smyth found that the drift of migrating yellow butterflies in that region of Alabama is always toward the southeast. He hopes to determine where they come from and how far and how fast they travel by these stamped identification marks.

Factors Affecting Insect Propagation.

Dr. C. H. Curran, Associate Curator of Entomology at the American Museum of Natural History has described several interesting factors which occur during the life cycle of the tropical botfly. An interesting phase of the cycle depends on the mosquito as an accomplice. When the female botfly is ready to deposit its eggs, she haunts an area where mosquitoes are emerging from pupation. The botfly holds the recently emerged mosquito and proceeds to deposit eggs on the body of the mosquito, which then acts as a carrier for the eggs of the botfly to the warm-blooded victim of the mosquito.

Considerable speculation as to the survival of Anophelines through the dry season in Panama has been made in previous years. It is a well recognized fact that some breeding occurs during the dry season but the sudden increase in larvae and adults seven to ten days following the rainy season onset cannot be accounted for as coming from these sources. Hence, it has been felt that hibernation of eggs might be one of the factors involved in the survival of this species. Heretofore this has not been demonstrated but Doctors Stone and Reynolds of the Army Medical Research Board now have some evidence which seems to indicate this means as a possibility. They collected earth from a number of areas which had been dry for at least one month and placed these samples of earth in sterile pans and covered each with water to which hay infusion had been added. This material was then protected so that no mosquitoes from an outside source could gain access. Several days later they obtained larvae of several species from the pans. These simple experiments offer evidence which might indicate hibernation as a possibility.

Several investigators from the Bureau of Entomology and Plant Quarantine, U. S. Department of Agriculture, while making a study of factors affecting the hatching of mosquito eggs, found that only a relatively small percentage hatched when flooded with unmodified tap water. Yet these eggs were found to hatch in nature when the areas in which they were laid are flooded. These scientists then assumed that the dead vegetation was an added necessity for egg hatching. To test their assumption they added infusions of dead leaves and grass to the tap water and as the result, increased the egg hatches quantitatively. Then, in an effort to determine the nature of the egg-hatching stimulant, they added a number of amino acids and proteins to the tap water and found these chemicals capable of increasing the egg hatch.

Physiological Characteristics in Entomological Classification.

Dr. N. A. Weber of the University of North Dakota has described the sting of an ant which occurred while he was on the Barre Colorado Island in the Panama Canal Zone. Dr. Weber was also the victim of an ant sting several years previous while in British Guiana. He compares the ill effects resulting from the two incidents and it is of interest to note that, while the ants were of the same species, the virulence of the sting was considerably different. Dr. Weber cites these two incidents as examples of physiological differences which seem to be unaccompanied by obvious morphological characters. Hence, it is probable that students of insect taxonomy may sometime add numerous physiological characteristics to the many morphological characters now in use in insect classification in an effort to increase still further the entomological species known.

Insect Control.

Chemists and entomologists have continued their work in the discovery of chemicals which will destroy insects which are harmful to various plants. As an example, the Bureau of Entomology and Plant Quarantine reports several methods of combating worms which enter ears of corn. The first method is to discourage the earworm by implanting tablets of hexachlorolthane into the tip of the ear. The chemical fumes given off thus destroy the worms. The second method is to spray mineral oil on the silk of the corn so as to smother the small worms and drive the larger ones out. It is reported that the red spider, a menace to plants, can also be controlled effectively by a chemical derivative of cyclohexylamine. See also ZOOLOGY.

1938: Entomology

Important developments have marked the year 1938 in all fields of entomological research, ranging from the practical aspects of medical and economic entomology to those of the more general fields of embryology, genetics, and physiology.

Disease-bearing Insects.

After the demonstration by Walter Reed and his associates that yellow fever is carried by the Aedes aegypti, it was thought that eradication of the disease through mosquito-control measures was possible. While this method has been successful in the United States, other countries, such as Africa and South America, have continued to suffer from outbreaks of this disease. It has been shown that the chief reason for these continued outbreaks is that the yellow fever virus can be carried by insects other than the aegypti mosquito. This has been recently demonstrated by a group of Rockefeller scientists working under the Cooperative Yellow Fever Service of Brazil and the International Health Board. And scientists at Harvard and Cornell Universities have shown that one of our own widely distributed species of mosquitoes (Aedes triseriatus) is also capable of carrying the yellow-fever virus. However, there appears to be no immediate danger from this source, because the ability to carry the virus has only been demonstrated in the laboratory, and this species of mosquito is probably not a natural carrier of the disease.

Another front in mankind's war against insects also seems to give some promise of victory — that in Africa against the dreaded tsetse fly. This insect is a bearer of the deadly African sleeping sickness, and a scourge to humans as well as to livestock. The discovery of the high value of a larvicide as a tsetse-fly repellent was made by a recent American expedition to Africa. The larvicide was originally developed for the control of mosquitoes in New Jersey by Dr. J. M. Ginsburg, a biochemist from Rutgers University.

A serious insect pest in the vineyards has been found to be susceptible to the fatal lure of a pale blue light. This work was reported by J. K. Ellsworth of the University of California. The interesting fact brought out in this series of experiments is that the female grape leafhopper seems to respond more readily to the blue light than do the males. While the factors responsible for this sexual differentiation to light have not been explained, the results can still be termed a success from the economic viewpoint, in that it is the females which in turn produce the new crop of leafhoppers.

The deer botfly's speed has been widely reported as being approximately 800 miles per hour. This now seems to have been completely repudiated by the experiments of an engineer. Dr. Irving Langmuir, of the General Electric Company's research laboratories. Dr. Langmuir proved that this speed would be an impossibility on the basis of his theoretical calculations and laboratory experiments. He states that if such a high speed were attained by this insect, it would consume one and one half times its own weight in food every second in flight, which would be impossible. Furthermore, if the insect struck human flesh at 800 miles an hour, it would exert a force of 310 lb. and be a fairly efficient bullet, causing a serious wound. Such wounds have never been reported. His experiments also showed that, at a speed of 64 miles per hour, the deer botfly would be invisible. Hence. Dr. Langmuir concludes that 25 miles per hour would be a more reasonable speed for this species of insect. Also, in regard to the speed of insects in flight, a well-known New Zealand entomologist, Dr. R. J. Tillyard, observed the speed of a dragon fly over a measured course and found its speed to be 60 miles per hour. Other scientists report speeds of flying insects of various species to be between 18 and 33 miles per hour.

Experiments on Protective Coloration and Food Specificity.

Despite recent claims to the contrary, Dr. Isley of Trinity University, Waxahachie, Tex., has shown that protective coloration of insects really does protect them against their more common enemies, the birds. Dr. isley's experiments showed that 88 per cent of the various insects that contrasted with their backgrounds were found and eaten by the birds, whereas only 40 per cent of the insects were eaten by the birds when the backgrounds harmonized with the insect's own color.

Dr. Isley has also carried out another series of interesting ecological studies. He made observations on the food of some forty species of grasshoppers and found that 50 per cent were primarily grass feeders. The other 50 per cent chose their host plants from the forbs or broad-leaf flowering plants. The interesting phase of this series of observations seems to be that this food specificity is not only a physiological fact but also a morphological adaptation. Microscopic and macroscopic examination of the mandibles of these grasshoppers showed two chief patterns, and these two patterns conformed to the two general types of feeding habits of these forty species of grasshoppers.

Sense Organ Experiments — Hearing.

Interesting experiments in the study of special sense organs of insects has been continued this year. One study was made by Dr. F. L. Wells, of the Harvard Medical School. He has shown that spiders can hear at least some of the sounds audible to the human car. He tested a number of species of orb-weaving spider with the use of a tuning fork of medium pitch, holding the instrument close to them but not touching them. The spiders showed various consistent responses, ranging from slight leg movements to actual attacks upon the fork, as if it were an insect.

Studies on Insect Development.

Studies on the chromosomes of the salivary gland cells of certain insects is being continued by the school of scientists at the Carnegie Institution of Washington in an effort to more firmly establish the structural units of these small strands of nuclear material, which are so important as bearers of hereditary characteristics in all forms of life. Also in connection with these studies in cytology other studies on the determination of structural units and factors which influence developmental changes during the life of the insect are being carried out in a number of research institutions. The results of these studies on insect development serve as additional stimulation toward speculation concerning the problem of development in higher animals, and also to emphasize the importance which comparative embryology would have for a better understanding of these processes.

Cellular Experiments.

In the field of cellular physiology, the use of insects in the laboratory for determining the properties and potentialities of such substances as activators or enzymes, is being carried on more and more extensively each year.