The First Field Tests of Recorded Mosquito Sounds used for Mosquito Destruction 1,2 (1949)

Summary and ConclusionsIt seems reasonable to draw the following conclusions from the Cuba experiment and its background; 1. Female calls of wild-caught anophelines obtained from a cattle trap such as A. albimanus can be recorded, and a re-recorded test record obtained of sufficiently good quality to be effective for sound-baiting a trap to catch males of the same species. 2. The calls which seem of lowest pitch as judged by the human ear are seemingly the most effective for calling the males. 3. The female calls used are not sine-wave in shape but are quite complex, and are not audible ordinarily to the unaided human ear. 4. A test record of female sounds as described in (1) will cause males of the same species to fly in the direction of the loudspeaker. An electric screen (high-voltage-charged) can be placed forward of the loudspeaker for the purpose of killing the mosquitoes that fly toward it. The characteristics of the power supply chosen for the screen can be of such nature as to cause practically no damage or distortion in the killing process that may interfere with the accurate identification of the species and sex of the mosquitoes killed. 5. The mosquitoes so electrocuted are predominantly males (90 per cent) of the species for which the female call is recorded and played. 6. The playing of such a record will also attract frogs, chameleons, bats, dragon flies and other forms of life that prey upon the mosquitoes for food. Certain will be attracted and killed (tree frogs, chameleons); others (bats, dragon flies) will dart around but will not be killed as they do not touch the electric screen. 7. Neither the light flashes produced by the electric discharges, nor the ozone produced seem to have any affect in attracting or repelling the subject mosquitoes. 8. The peak flight time of Anopheles albimanus occurred substantially at the same time during each evening of the test (7:15 PM local Cuban time). 9. The numbers of mosquitoes trapped during a peak period of ten minutes exceeded the number of mosquitoes taken from a cattle trap in a week or more. 10. The numbers of mosquitoes trapped each night varied over a fairly wide range from night to night. 11. The playing of such records seemingly will not induce flight activity in male mosquitoes at times when they are not normally active, but will, during periods of normal activity, alter their flight course so that such insects can be killed in a trap. 12. The sound level used in reproducing the records for a sound-baited trap may be quite high compared with the sound level that the mosquito normally utilizes in nature, but it may not be indiscriminately high as there appears to be an upper threshold beyond which a repellant action may take place. Under very quiet natural conditions, the sound level at this upper threshold is such that the sounds can be heard by an unaided human ear some one-fourth of a mile away. It may prove impracticable to use sounds above this threshold for repellant purposes as their unpleasant nature is objectionable. 13. Peak flight time occurred about 20 minutes after official sunset time. At this time the light level measured on a Weston Master II Exposure Meter was about 0.2 candle per sq. ft. 14. Automatic electrical counting of the electric screen discharges is practicable and whenever possible should be used in the collection of counting data in future field experiments. The electrical count should be compared with the count of mosquitoes found on the sheet in the trap. 15. Sound recording techniques may make possible a valuable quantitative sound-activity index for measuring the sound activity of a particular species of mosquito. Such indices may be derived statistically from the curves automatically traced by an instrument such as an Esterline-Angus continuous-writing DC milliameter energized from a suitable electronic rectifier and filter integrating sound level with time. The electronic rectifier and filter mentioned is energized from the output of the sound recording equipment (capable of recording single insects) that is set to operate continuously over 24 hours or other specified intervals. This method can measure quantitatively regardless of species and sex. 16. Playback of the sound recordings of female mosquitoes to males of the same species under natural conditions (such as in a swamp) can provide a valuable quantitative activity index based on flight. This flight activity index may be compared with the sound activity index of item 15 for statistical correlation. Playback of the sound recordings of one sex to another may be made in the laboratory to measure the sound response to obtain a sound response index, another potentially useful activity index. 17. Electrical insect-killing methods seem selective, and an arrangement that is effective for one kind of insect, say a fly, may not be satisfactory for another kind of insect, say, a mosquito or a beetle. Important factors are: a. Peak voltage b. Energy released per discharge c. Nature of the current with regard to frequency and waveform 1. Line frequency alternating current (60 cycles per second or other) 2. The discharge from a capacitor previously charged to a high voltage (The discharge rate may be quite important). 3. The discharge of an ultra high frequency generator (functioning at say, 50 megacycles per second). 4. Other (e.g. a "spike" generator—such as is used in radar). For mosquitoes where a minimum of distortion is desired due to electrocution, the simplest arrangement using line frequency alternating current is satisfactory although it may be definitely lethal for accidental contact of human beings or farm animals or the like. 18. It is possible that the heavily haired male antennae act as a receptor mechanism for sound emitted by the female. 19. The sounds are substantially species specific, Aedes will not respond to Anopheles or vice versa.