Sex Attraction in the House Fly, Musca Domestica L.-

Attraction tests have shown that virgin female house flies attract both virgin males and females but the degree of attraction is relatively small. A tentative hypothesis of chemical sex attraction is suggested. The attraction does not appear to be due to moisture, motion, or sound effects. INTRODUCTION The development of insect strains resistant to various insecticides has created such serious problems that entomologists have had to consider concepts of insect control that are radically different from any previously devised. Control or eradication by sterilization of pest populations is one such concept that has proved to have considerable merit (Bushland, 1960). Basic research on insect behavior has led to the development of other possibilities, such as the use of insect attractants in combination with insecticides, pathogens, or chemosterilants to increase the efficiency of a control program. Green et al. (I960), Jacobson and Beroza (1963), and Beroza and Green (1963) have reviewed the recent, advances in the field of insect attractants. Interest in sex attraction in particular has increased and considerable effort has been given to the discovery and identification of sex lures with the idea of utilizing them in the control of certain species. A discussion of insect sex pheromones is given in the paper by Karlson and Butenandt (1959). Superficial observations on the mating behavior of the house fly give little indication that chemical attraction is of great importance in the sexual activity of this species. Males often attempt to mate with other males and will do so even in an environment free of females or a female scent (Murvosh et al., 1964). However, this behavior, in itself, does not disprove the existence of a chemical "sex attractant" or copulation stimulant. This paper represents a continuation of our previous studies on house fly mating behavior and gives the results of preliminary investigations in which evidence of the existence of a house fly sex attractant was found. METHODS The sex attraction experiments were performed in a large cage-type olfactometer (chemotactometer would be a more precise term, but is still not fully descriptive, since rheotaxis, sound, and motion may also affect the behavior of the test insects). The apparatus and procedure were similar to those used by Gouck et al. (1963) for testing mosquito attractants. Briefly, the unit consisted of an 18-mesh wire cage (6 ft x 3.5 ft x 6 ft) with aluminum frames. At one end of the cage, 2 ft from the top, there were two apertures, 3 in. in diameter, spaced 10 in. apart. Two glass cylinders (3 in. x 8 in.), each containing an inverted wire cone trap, were placed on a wood frame that moved so the glass traps would slide into position over the apertures in the cage. A 16-in. fan, at the opposite end of the cage, was used to draw a current of air through the glass traps and then across the cage. In order to achieve the air stream, it was necessary to seal the whole cage tightly with large plastic sheets, except for the glass trap area and fan sections of the cage. The test was designed to determine the percentage of "responder" flies in the cage Conducted in part with funds transferred from the Medical Research and Development Command, Office of the Surgeon General, U. S. Army. Manuscript received December 14, 1963. THE OHIO JOURNAL OF SCIENCE 65(2): 68, March, 1965. No. 2 SEX ATTRACTION IN THE HOUSE FLY 69 that entered the glass traps containing the "attractor" flies. Preliminary tests showed that the entrance of responder flies in the traps was dependent upon the presence of both an air stream and attractor flies in the traps. One hundred attractor flies were exposed in each glass trap; the cage contained 400 responder flies in experiments 1 and 2 and 500 in experiments 3 to 8. Usually, each experiment was replicated 3 times, but some were replicated 5 or 6 times. Each exposure lasted an hour. After each exposure, the glass traps were replaced with others that had been decontaminated in a detergent wash, fresh water rinse, and acetone rinse, and the positions of the traps were alternated to offset the effects of a favorable position. The light falling on the traps was measured with an expOvSure meter and balanced by moving a series of gooseneck lamps. One ml of water was injected into each trap on the glass surface at the start of each test to equalize any possible moisture effects. All flies were virgin a t the time of testing. A supply of food and water was always present in the cag-e. The temperature and humidity of the test room could not be controlled. RESULTS AND DISCUSSION The results are given in table 1. Experiments 1 to 3 were designed to see whether mature virgin males were attracted to either virgin males or females;