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.