Nature’s chemical messengers

StoryImage( ‘/Images/Story//img-ibmeEzPECo.jpg’, ‘Photo by Dr. Robert A. Hedeen’, ‘A pheromone-baited trap for Japanese beetles is bulging with dead beetles, but enough escaped the device to defoliate a nearby plant.’);

The biological definition of a hormone is a chemical substance that is produced in one part of a living organism’s body and is carried by the blood stream to another part of the body, where it produces an effect. A pheromone is a chemical substance that is produced by an individual and is discharged to the environment, where it affects another individual.

The use of these chemical communicators is common among organisms, and, as a great deal is still to be learned about them, pheromone research is an active field of biological investigative work. The substances employed range from the sex attractants produced by a single cell alga named Chlamaydomonas to Chanel No. 5 and Ma Griffe and other body fragrances designed to be used, for obvious reasons, by females and males of the human species.

The basic research on pheromones and their actions began in the early ’30s with insects, but it was not until 1959 that the chemical composition of a pheromone was first determined. It is not surprising that this pheromone was isolated from an insect, and much of the research in this field has been concerned with the idea of using pheromones to outwit and control bugs of economic and medical importance.

I vividly remember my introduction to the importance of pheromones in insect control when I visited the U. S. Army’s Quartermaster Corps’ research and development laboratory at Natick, Mass. (the Quartermaster corps is charged with the development, procurement, and issuance of pesticides). Scientists at this lab had successfully isolated a sex attractant type pheromone from the female German cockroach, Blatella germanica, and a demonstration of its effectiveness had been prepared.

On a table the researchers had positioned a 6-foot cube made of clear Plexiglas that was swarming inside with thousands of this common household pest. A superficial examination revealed this teeming mass of potential disease carriers was composed of about a 50-50 ratio of male to female cockroaches.

The project director then proceeded to fill a microsyringe with a drop of fluid he said contained one millionth of a gram of female roach pheromone that had been meticulously isolated from countless female roaches. He then proceeded to inject the material into the cube through a minute safe pore at the bottom of one corner. Chaos among the roaches resulted immediately. In an instant, about half the insects made a mad descent to the corner of the cage and formed a disgusting mass, struggling to make their way as close to the pheromone as possible. I was asked to determine the sex of the roaches who were so profoundly affected by the pheromone. Though the insects were in the throes of heated passion, I could not spot a single female in the frenzied mass. Rather, the females were calmly resting on the side of the cube, apparently enjoying the reaction of the males to their pheromone.

It did not take an over-active imagination to see how sex attractant pheromones could be put to good use in insect control. Roaches are difficult to exterminate with relatively safe household pesticides. But, if an extremely powerful, concentrated insecticide could be placed in a protected area and the sex pheromone added, the male half of a roach infestation could quickly and effectively be eliminated.

Sex attractant pheromones have proved to be a bonanza in the control of certain moths and other types of insects. It has been used quite effectively against that notorious defoliator of forests, the gypsy moth. Next to the boll weevil, the pink boll worm is the second-worst enemy of cotton in certain areas of the South. Traps using a pink bollworm pheromone have been highly effective in controlling this devastating cotton insect. It should be pointed out that, as far as what has been learned to date, pheromones are specific for each type of living organism. In other words, the roach pheromone will not work on the gypsy moth and vice versa.

Fortunately (or unfortunately), the sex pheromone of the hated Japanese beetle that is attacking all types of plants in the Rock River Valley at this time has been isolated and synthesized. It is incorporated into the beetle traps we see in garden shops and are now hanging in many yards. There is no question about it, the traps destroy untold numbers of beetles, but they also attract tremendous numbers of the insects to our yards. Though many are trapped, many more avoid the intricacies of the trap and proceed to chomp away at our rose bushes and almost any other ornamental we may have.

Pheromone research with humans is still in its infancy, and they should be used with caution when one has the intention of attracting members of the opposite sex.

Dr. Robert Hedeen is a former resident of Maryland’s eastern shore and resided in the Chicago area from 1960 to 1971. He is a retired professor emeritus of biological sciences in the University of Maryland system. He has published more than 30 scientific papers, has written numerous magazine articles, and is the author of two books on the natural history of the Chesapeake Bay.

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