Fate of Houseflies Killed In
By Donald E. Weidhaas, PhD, RPE and Phillip B. Morgan, PhD
(See Short Biography of Authors Below)
Three separate tests were conducted to determine the fate of house flies responding to and electrocuted in light traps (601T type supplied by Don Gilbert Industries, Inc.). The tests were run in motel rooms in which 2 light traps were placed in each end of the room and left operating for approximately 24 hours (from one morning to the next). In the three tests only 1% of the flies were not trapped either in sticky panels or the light traps.
Damage to the flies from electrocution in the light traps was seen as the separation of some legs from the body and the loss of wings or parts of wings. The majority of flies showed no damage from electrocution. Seventy-two percent of the flies showed no loss of legs; 60% of the flies showed no damage to the wings. When flies showed loss of legs, the legs were found whole and intact in the tray of the light trap or within 6" of the light trap. The legs lost included pro-, mesa-, and metathoraxic legs. Most of the affected flies lost only one leg, but some lost 2, 3, or all 6 legs. When flies showed effects on the wings, damage to the wings varied from >10% loss of wing surface to the loss of the whole wing. Wings or parts of wings as well as legs were found in the trays of the traps or within 6" away from the traps.
No contamination of body parts of flies were found more than 6 inches away from the traps. White sticky panels placed in 15 locations in the room and examined by eye, handlens, and microscope showed no fly body parts or evidence of contamination away from the trap.
Since it has been reported that small microscopic particles have been detected in electrocution of flies, it may be possible that some of the missing wing parts are a source of these particles because they are singed in the process of electrocution. In practice the small amount of wing material involved would seem to be inconsequential.
OBJECTIVE OF THE STUDY
Houseflies attracted to the light traps equipped with electrocuting grids are killed by contact with the grids. Such contact produces a surge of electricity through the body as the fly makes simultaneous contact with the parallel grids. A literature search produced no specific citations which described the effect of such a surge of electricity through the fly body while it was stunned and killed. Therefore a study was initiated to evaluate the fate of flies exposed to electrocuting light traps, particularly to determine the fate of the fly body and its parts after stunning and killing by electrocution. The traps used in this study were model 601T supplied by Don Gilbert Industries, Inc. According to the manufacturer when a fly hits the grid of this trap it produces approximately 4500 v at 9.2 MA.
PLAN AND PROCEDURES
The plan of work and experimentation was simple. Adult houseflies of both sexes and 1 to 6-days-old were released into the motel rooms. The number of flies per room was only estimated from the number of flies thought to be in the cage before they were released. The exact number per room was determined after each test was completed by counting the dead and any surviving live flies. Since each room was closed until the final count none of the flies could have escaped.
Three replications of the test were planned; each consisting of one motel room as a control containing no electrocuting light trap and one room as the test room with 2 electrocuting light traps. After the first test it was obvious that the control room added no significant information to the test so it was discontinued.
The test room was a standard motel room (approximately 11 ft. by 22 ft.) with two double beds on each side of a night stand on one wall and a long desk type table and a TV set on the wall opposite the bed. One of the narrow walls had a large window next to the entrance door with the heater-air conditioner under the window. At the opposite end of the room from the window there was a cabinet, sink and mirror. The toilet and bathtub and shower were in a separate small room. The door to the bathroom remained closed so that the bathroom was not part of the test area. A short video tape of the room and the position of the cages was taken.
Two electrocuting light traps (model 601T) supplied by Don Gilbert Industries, Inc. were placed in the test room. One was placed in front of the window on the entrance wall of the room; the other was placed in front of the sink at the opposite end of the room. Beneath and around each trap a clean white sheet was placed for later examination. White cardboard panels with sticky top surfaces (obtained from Olson Products, Inc.) were positioned in various places in the room. Two large sticky panels ( 9" x 11") were placed 1 foot in front of each light trap on the white sheet. Three small sticky panels (3" x 5") were also placed on the sheet in front of each trap and from 1 to 2 feet from the trap. Another 8 small sticky panels were positioned around the room: 3 on each of the two beds and 1 each on the TV, the night stand and the desk. The purpose of the sheets and the sticky panels was to provide samples of surfaces which could be examined by eye, handlens or microscope for evidence of any fly body parts that could have left the trap area upon their electrocution.
In the morning between 9 and 11 AM the rooms were prepared, the light traps turned on and then approximately 400 adult flies released into the room. The rooms were locked until the same time the following morning when they were examined.
The examination involved counting any live flies that may have survived, counting all dead flies, examining the sheet and sticky panels, and collecting the sticky panels for later examination.
As mentioned above the test was repeated 3 times during October and November, 1992. In the final test a second room was used as a control. In the second and third tests only one test room was used.
In the first test the room used as a control was setup the same as the test room, but had no electrocuting light traps. The 2 sheets, 4 large sticky panels, and 15 small sticky panels were placed in the same locations as those in the test room. On the morning following the release of flies into the room there were still 87 live flies in the room surviving without access to food or water. The large and small sticky panels had trapped 237 of the flies. Of the 345 flies released, 75% had been trapped in the sticky surface of the panels placed throughout the room; while 25% had survived both the hazard of the sticky surface and the lack of food and water. Examination of the sticky panels and the sheets by eye and handlens showed no evidence of contamination by fly parts except, of course, for the whole intact flies stuck in the adhesive.
In the first test only 1 (.2% of the total of 438 flies released into the room) live fly was found in the test room the morning following their release. Interestingly, of the 437 dead flies found, 394 (90%) were caught in the electrocuting light traps and 43 (9.8%) on the sticky panels. Eye and handlens examination of the sheets and sticky panels showed no evidence of contamination from electrocuted flies outside of the immediate area of the traps.
Examination of the traps and their trays showed fly legs and wings detached lying in the tray. Data on the damage recorded in the flies electrocuted in the trap is summarized later.
In the second test 411 flies and in the third test 486 flies were released into the test room. A summary of the number and percent of live and dead flies and where they were found is included in the following table.:
It is interesting to note that in Test 2 and 3 the percent of flies found trapped on sticky paper was higher and percent of flies found in the light traps was lower than in Test 1. During Test 1 the heavy drape over the window was left open; while in the other 2 tests it was closed. The effect of outside light on the movement of flies to the window and the trap is obvious. Wherever the flies were trapped the effectiveness of the light traps was very high. When the drape was closed, the movement of flies to the window was slower allowing more flies to be caught on the sticky panels in their movement around the room.
The main purpose of the study was not the effectiveness of the traps, but the fate of the flies attracted to the traps and electrocuted. Examination of all of the sticky panels by eye, handlens or microscope failed to show the presence of fly parts or pieces. Since the sticky panels were placed throughout the room to within 1 foot of the traps we conclude that no fly parts or pieces were scattered from the traps as they were subjected to electrocution in the trap. The flies responding to the trap were not exploded into pieces.
In the 3 tests 1,070 flies (294 in test 1; 303 in test 2; and 373 in test 3) responded to the traps and were electrocuted. They were found mostly in the trays that were part of the traps. A few flies (8 were found under the tray, but in the trap). A few flies were found on the sheets within 2 feet of the front of the trap (cover photo). The photo below shows the flies and parts in the tray.
The 1,070 flies were subjected to handlens examination and samples of them to microscopic examination. The trays were also examined. In the trays there were some whole intact fly legs, wings and parts of wings that had become separated from the body of the flies. Separate, but intact wings or parts and intact legs were found only in the tray of the trap or within 6 inches of the front of the trap.
Flies from Test 1 were examined to determine the type of damage that could be identified in the flies responding to the trap. In all flies the head, thorax and abdomen were still attached. Whole legs were found lying in the tray; approximately 75 - 100. These legs were intact and had become separated at their membranous body connection. Individual wings were found on the tray floor. Most of the flies were intact with all body parts intact and appeared normal, except that some wings showed evidence of being singed.
The damage to the fly bodies in terms of missing legs and wing damage was quantified in tests 2 and 3. The results are summarized in Tables 1 and 2. Each fly attracted to and electrocuted in the light trap was examined under handlens. The number of legs missing was noted and recorded as the number of pro-, mesa- or metathoraxic legs missing. As noted above the legs that were missing were separated at the membrane connecting the leg to the body. Legs fell into the tray and were intact as whole legs. Results in Table 1 summarize the results of flies from the 2 different traps and 2 different tests. Trap 1 was the one placed inside the room near the sink. Trap 2 was the one placed in front of the window. In spite of the fact that a heavy drape was drawn, the trap near the window caught more flies than the one not by the window. Seventy-two percent of the flies had no legs missing. Of the 28% of the flies missing legs, none had lost 3,4 or 5 legs. More flies were missing 1 leg than 2 legs. Six flies had lost all six legs. Since the legs were found intact in the cage trays or on the sheets within inches of the traps, the fact that some 28% of the flies lost 1 or more legs which were whole would not constitute a contamination problem. Forty three percent of the flies showed some damage to their wings. Table 2 summarizes the results of examining flies for wing damage from Test 2 and Test 3. Examination of a sample of flies from sticky panels in the test room which had not been electrocuted showed that 13% (6 of 46) showed 10% or less wing damage. Thirteen percent of the electrocuted flies (table 2) showed 10% or less damage to their wings. Thirty percent of the flies showed more than 10% wing damage which is attributed to electrocution. The damage was visible by the absence of part of the wing. As mentioned above a few complete wings were found in the cage trays; smaller parts of wings could also be seen. It is also possible that some of the delicate wing membrane was burned sufficiently to cause small microscopic particles to form.
The limited amount of damage to the wings would suggest that contamination from such an occurrence would be minimal.
Qualitative examination of flies trapped on sticky panels (not subject to electrocution) and flies from the light trap (electrocuted) under the microscope showed no damage to the flies, their body parts or the many hairs of the body of the fly other than the effect described above, i.e. the loss of legs, wings or parts of wings.
Table 1. Summary of the loss of legs from houseflies after electrocution in light traps.
Table 2. Summary of the loss of legs from houseflies after electrocution in light traps.
Donald E. Weidhaas, PhD, RPE
Retired head of the U.S.D.A. Insects Affecting Man and Animals Research Laboratory (Gainesville, Florida); B.S. Chemistry, University of Massachusetts, 1951; Ph.D., Entomology, Cornell University, 1955. 29 years experience in the biology and control of insects with a specialty in research and medical/veterinary entomology with the U.S.D.A. Experience includes research management and collaboration with industry, state, and national organizations. Author of over 140 technical publications. Consultant to national and international organizations.
Served for 30 years as a Research Entomologist at the U.S.D.A. Insects Affecting Man and Animals Research Laboratory (Gainesville, Florida); A.B.Zoology, Fort Hays Kansas State College, 1950; M.S. and PhD in Entomology, Kansas State University, 1957 and 1960 respectively. Developed new concepts and techniques for utilizing biological control to control filth breeding flies at poultry, beef, swine, dairy, and equine installations. As an expert in biological control, advised private organizations, state and federal agencies, as well as, foreign governments on the use of biological control to suppress houseflies, stable flies, and other filth breeding flies at agricultural installations. Authored and co-authored 74 scientific publications on biological control, chemosterilants, insecticides, genetics, insect growth regulators, and gamma radiation. Last we heard, he was managing farming interests in northwest Kansas.