| Abstrakt: |
Some 40 or more years ago, there was evidence of interest among scientists in the sounds of mosquitoes. Despite very crude acoustical apparatus, significant conclusions had been reached by the early investigators. Although very little was done in the next three decades despite the growth in the field of acoustics, interest has recently been renewed because of the world-wide need to check the spread of mosquito-borne tropical diseases. Recent experiments have confirmed many early findings and have provided valuable new data. Mosquito sounds are distinctive; gross differences occur that are readily detected both by listening and by wave analysis. All fundamental sounds occur in the center of the sonic range (200-1000 e.p.s.); all are rich in harmonics. All sounds are warble-modulated, some at a single low rate in the order of 5 c.p.s., others at a double rate with the same lower rate and a higher rate in the order 5 times the lower. In some tones, some harmonics are completely interrupted while the fundamental remains undisturbed. Warble amplitudes are quite large; 20 percent is not unusual. The fundamental pitch often drifts; in one case, for example, there was a 25 percent increase in as little as 0.05 sec. Male sounds seem higher pitched than female; sound spectrograms show this to be due more to the difference in harmonic emphasis than to the difference in fundamental pitch. Generally speaking, mosquitoes do not generate or respond to sine-wave tones. Mosquito sounds are low in energy level; the total sound power output of a female Anopheles albimanus whose sound was used to bait a mosquito-killing trap in Cuba was in the order of 10-13 watt. With this low power level it is difficult to obtain recordings with the high signal-to-noise ratios customary in high quality commercial recording because of the relatively high noise levels. Despite this handicap, it has been possible to reduce the noise due to microphonics, hum induction, vibration, and airborne and other disturbances to the point where recordings with 40-db signal-to-noise ratio are made frequently. [ABSTRACT FROM AUTHOR] |
