Objective To evaluate the larvicidal effect of ultrasonic waves against Aedes albopictus larvae at various exposure parameters (distance and time), and to preliminarily investigate the effects of different containers (water volume and depth) and ultrasonic devices on the larvicidal efficacy, so as to provide experimental evidence for the application of ultrasound-based mosquito control technology.

Methods Under controlled laboratory conditions, two commercially available ultrasonic devices 40 kHz/300 W and (50±5) kHz/70 W were used to systematically examine the effects of exposure distance (20, 40, 60, 80, and 100 cm), exposure duration (1, 3, 6, 15 and 60 min), larval instar (Ⅰ‒Ⅱ and Ⅲ‒Ⅳ）, and container type on the immediate mortality of Aedes albopictus larvae collected from urban areas of Shanghai. Statistical analysis of the mortality rates of larvae among different experimental groups was performed using the chi-square test.

Results Ultrasonic exposure exerted a detectable larvicidal effect against Aedes albopictus larvae of all instars. For early-instar larvae, exposure time significantly affected mortality at all tested distances (20, 40, 60, 80 and 100 cm), with χ² values ranging from 25.57 to 32.74 ( all P<0.001). No significant distance effect was observed in the first and second instar larvae after short-term exposure (1 and 3 min; P>0.05). However, a distance-dependent effect emerged from 6 min onward (P<0.05). During short-term exposure (1 min and 3 min) at close range (20 cm and 40 cm), the immediate mortality of the third and fourth instar larvae was higher than that of the first and second instar larvae. Conversely, during prolonged exposure (15 min and 60 min), the first and second instar larvae exhibited significantly higher mortality than that of the third and fourth instar larvae. These results indicated that larval mortality was jointly influenced by exposure duration and distance. Preliminary experiments indicated that larvicidal efficacy in shallow water was lower than that in deep water. No significant difference in larvicidal effect was observed between the two ultrasonic devices with different frequencies and power outputs.

Conclusion Under laboratory conditions, ultrasound can effectively kill Aedes albopictus larvae, and the larvicidal effect is jointly influenced by larval instar, exposure distance, and aquatic environment. Compact ultrasonic devices show potential for field application in biological mosquito control.