Summary of Findings
Vero Beach Trials
August 10th to 14th 1998
October 7th to 15th 1998
1. Introduction
Prior research under a Cooperative Research and Development Agreement (CRADA) between the United States Department of Agriculture, Agricultural Research Service (USDA ARS) and BioSensory, Inc. succeeded in demonstrating that computer models can accurately predict how many mosquitoes and biting midges will respond to a given combination of biological attractants. Combinations of the three most powerful attractants: Carbon dioxide (CO2), octenol, and infrared radiation (heat) were studied extensively. When attractant combinations that produced the most efficient lure were identified, researchers turned their attention to the development of electrocuting girds to surround the lure.
This research is directed at identifying electrocuting grid configurations and materials capable of hygienically destroying mosquitoes and biting midges. Hygienic electrocution requires the destruction of the insect with its exoskeleton intact, unlike backyard "bug zappers" that explode the exoskeleton, spraying fragments into the air nearby. In addition, there are a number of technical challenges associated with the electrocution of mosquitoes, and especially biting midges, which have a maximum wingspan of 1.5 mm.
The results of the trials and conclusions drawn are presented such that they do not disclose patentable features of the Dragonfly's electrocuting grid.
2. Method
Location
The study took place at the University of Florida Medical Entomology Laboratory at Vero Beach Florida. The laboratory is a 103-acre wilderness preserve for research on disease vectors.
Figure 1: University of Florida Medical Entomology Laboratory
Personnel
A USDA ARS technician preformed the fieldwork for the August 1998 trials under the supervision of Dr. Daniel Kline. Dr. Kline is a USDA ARS researcher at the Center for Medical, Agricultural and Veterinary Entomology at Gainesville, Florida. The technician was unavailable for the October, 1998 fieldwork, which was preformed by a student and an Indian River Mosquito Control worker. Dr. Richard Darsie, author of Mosquitoes of North America, assisted with on-the-spot identification of species in the field during the October trials.
Experimental Control
A CDC trap was run each night as a control. The CDC trap releases 200 ml/min CO2, which is equal to the respiration of a 90-kg (200-pound) person.
Figure 2: CDC Trap and CO2 Bottle
The CDC trap is made up of a battery powered fan protected by a "pizza lid" to shield collections from rain. The fan exhausts into the plastic jar beneath the CDC trap, which contains a pesticide strip. Flexible tubes carry CO2 from the bottle to the CDC trap where it is discharged
3. August, 1998 Trials
The experimental design was a 2x4 Latin Square. A Dragonfly having an 'S' Type electrocuting grid and the control, a CDC trap, were rotated among each of four locations having electrical outlets. The locations are equally spaced along the trail between the Vehicle Port and the Boathouse (Figure 1). Analysis of collections by station in previous research revealed greater mosquito populations at the two locations nearer the Vehicle Port, and greater biting midge populations at the two locations nearer the Boat House.
Trials were repeated twice. The Dragonfly and CDC trap were run for 13 hours during each trial, beginning at 6:00 PM and ending at 7:00 AM the following morning. Tape was affixed to the Dragonfly (Figure 3) to reduce the number of specimens blown away by sea breezes and carried away by ants.
Figure 3: Dragonfly Setup
The Dragonfly has adhesive tape around the base to prevent dead insects from blowing away with sea breezes.
Dragonfly collections were removed in the following manner. The Dragonfly was placed on a table covered by glossy white posterboard. First, the tape was removed from the Dragonfly. Insects on the tape were counted and recorded, but no attempt was made to remove them from the tape. Second, insects in the Dragonfly collection tray were placed on the posterboard and counted. Third, a #10 artists brush was used to remove insects from the Dragonfly electrocuting grid and internal surfaces. Insects removed from the Dragonfly fell to the posterboard and were counted. Insects were placed in pre-labeled petri dishes and frozen.
CDC collections were captured in a plastic jar containing a strip of insecticide. The jar attaches beneath the trap's battery powered fan (Figure 2).
Specimens were sent to Dr. Kline in Gainesville who verified the count and identified the collection by species. The predominant species were Aedes taeniorhynchus, the Black Saltmarsh mosquito, which accounted for 53% of collections, and Culex nigrapalpus, an encephalitis vector, which accounted for 22% of collections.
4. October, 1998 Trials
The experimental design was a 4x4 Latin Square using three Dragonfly traps having different electrocuting grids: Type 'S', Type 'P', Type 'C', and the control, a CDC trap. Each trap was rotated through each of the four locations along the trail from the Vehicle Port to the Boathouse (Figure 1). One set of trials was completed.
The predominant species were Culex nigrapalpus, which accounted for 82% of collections, and Deinocerites cancer, which accounted for 11% of collections.
All other methods were identical to those used in the August trials.
5. Results
Figure 4: August Mosquito Collections
Although the Dragonfly uses ¼ the CO2 of the CDC trap (50 ml/min vs. 200 ml/min), it was expected to match the CDC trap's performance. While the 'S' Type electrocuting grid performed as expected in 3 trials, its collections were less than the CDC trap in 5 trials.
Figure 5: August Biting Midge Collections
Against biting midges, the 'S' Type electrocuting grid outperformed the CDC trap in 7 of 8 trials. In locations where biting midge populations were plentiful, 'S' Type grid collections were 15 to 68 times larger than CDC trap collections.
Because mosquitoes have a wingspan 4 to 6 times larger than a biting midge, it was hypothesized that the fine pitch of the 'S' Type electrocuting grid may deter endophilic species of mosquitoes from attempting to fly through it. Two alternative electrocuting grid configurations were proposed to improve performance.
The 'P' Type was configured such that it provided an unobstructed view of the Dragonfly's thermal lure, but intercepted the insect's circular flight paths around the thermal lure. The 'C' Type was a dual purpose design, intended to be equally effective against mosquitoes and biting midges. Trials of the alternative electrocuting configurations took place in October when, although mosquito and biting midge populations were lower, they were still adequate for comparative tests.
Figure 6: October Mosquito Collections
The 'P' Type grid was superior to the 'S' Type and 'C' Type grids in 3 of 4 trials. Moreover, the 'P' Type grid's performance was essentially equivalent to the CDC trap, with average collections of 298 and 304 mosquitoes, respectively.
Figure 7: October Biting Midge Collections
Each electrocuting grid outperformed the CDC trap in all trials, with the 'C' Type having larger collections than either the 'S' or 'P' Types.
6. Conclusions
Mosquitoes and biting midges collected included both nuisance species and public health pests.
Culex nigrapalpus, a St Louis encephalitis vector,
Aedes taeniorhynchus, the Black Salt Marsh mosquito
Aedes albopictus, the Asian Tiger mosquito,
Culicoides furens, a biting midge.
The Dragonfly 'P' Type electrocuting grid is more effective against mosquitoes than the other two configurations. Its effectiveness appears to be associated with three characteristics:
Larger pitch between electrodes,
Unobstructed view of Dragonfly thermal lure,
Grids arranged to intercept insects circling thermal lure
The fine pitch of the electrodes in the 'C' Type grid was effective against biting midges, but reduced collections of mosquitoes. Refinements to the design of the 'P' Type electrocuting grid will enhance its performance, but additional tests will be required to determine if it can be as effective against biting midges as the 'C' Type.
Hygienic destruction of mosquitoes and biting midges was achieved, and remaining technical obstacles associated with grid design were overcome. Additional field tests of the final design are required to verify its performance characteristics. The Dragonfly's efficiency (biting insects per volume of CO2 released) is such that, when programmed to discharge 300 ml/min to 500 ml/min CO2, it can achieve collection levels demonstrated to create a barrier against biting midges.
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