females. In the present study, the 12-min time-recording bite attempts started when the first bite occurred. The comparison between the mean values for the first 3-min cycle (repellers turned off) and the subsequent cycle, when they were turned on, showed a significant increase from 20% to 50% of the bite rates caused by the intermediate frequencies (from 9.6 kHz to 18.2 kHz). The repellers causing an increase were: MCONT (t= -5.9; df = 35; P < 0.05), KAWOA (t= -6.5; df = 35; P < 0.05), SOFT 1 (t= -3.2; df = 35; P < 0.05), SOFT 2 (t= -6.4; Depsipeptide
df = 35; P < 0.05), and SOFT 3 (t= -6.7; df = 35; P < 0.05). For the other three repellers there was a lower and non-significant (P > 0.05) bite rate increase: 7.7% for the SOFT 4 (t= -1.1; df = 35; P > 0.05), 8.3% for the SOFT 5 (t= -1.8; df = 35; P > 0.05), and 11.5% for the device MGUAR (t= -1.2; df = 35; P > 0.05) (Table 2). Comparing the second cycle (repellers turned on) with the third cycle (repellers turned off), a significant decrease in bite rate was found for some intermediate frequencies (from 11.8 kHz to 17.0 kHz). A significant decrease ranging from 15.9% to 25.1% has occurred in the test with the repellers: KAWOA (t= 4.5; df = 35; P < 0.05), SOFT 1 (t= 2.8; df = 35; P < 0.05), and SOFT 2 (t= 5.3;
df 35; P < 0.05). A non-significant and lower bite rate decrease, ranging from 1.3% to 12.4% was found for the other five repellers, namely MGUAR (t= -1.3; df = 35; P > 0.05), MCONT (t= 1.2; df = 35; P > 0.05), SOFT 3 (t= 0.9; df = 35; P > 0.05), SOFT 4 (t= -0.9; df = 35; P > 0.05), and SOFT 5 (t=-0.5; df = 35; P > 0.05) (Table 2). Comparing the third 3-min cycle (repellers turned off) and the subsequent cycle, in which they were turned on, the results showed a significant difference only in the bite rate of the mosquitoes exposed to the KAWOA device, resulting
in an increase of 33.7% (t= -5.8; df = 35; p < 0.05) (Table 2). In the present work, only the sound of the repellers was used as a variable. Although Clements (1999) pointed out that female mosquitoes are not believed to respond to acoustic stimuli, the vibration of antennal hairs of Aedes aegypti female provides evidence that they perceive sounds (G?pfert et al. 1999). According to Morton and Offenhauser Jr. 1949), mosquito wing beat sounds are composed of a well-defined fundamental frequency together with overtone. In some spectrograms, as many as 15 distinctive frequency bands may be recognized. All the presently evaluated frequencies are much higher than those considered as being audible to mosquitoes, but at least four frequencies match the harmonics of Ae. aegypti wing beat vibration; MCONT, SOFT 4, and SOFT 5, matching the female frequency (assumed to be 400 Hz) and SOFT 1, matching the male frequency (assumed to be 600 Hz). G?pfert et al.