Effects of an in-built ultrasonic device on Anopheles gambiae s.l mosquitoes in an indoor environment

Mosquitoes are major vectors of malaria and lymphatic filariasis in Nigeria. Several initiatives aimed at reducing the burden of these diseases yield little or no results. In order to make the ultimate goal of reduction or elimination of these diseases a success, there is an urgent need for alternative approaches to control mosquitoes. One of these approaches is the use of ultrasonic device for the control of Anopheles gambiae. The effectiveness of in-built ultrasonic device fixed in Air- Conditioner to expel and/or knock-down An. gambiae s.l mosquitoes was evaluated. The rate at which an ultrasonic device in an Air Conditioner (AC) expelled and knocked down Anopheles gambiae s.l mosquitoes was assessed in a Peet Grady (PG) chamber at the Institute for Advanced Medical Research and Training (IAMRAT), College of Medicine, University of Ibadan, Nigeria. Mosquitoes were bred in the IAMRAT insectary under standard rearing conditions. Three to five days old adults were used for the test. An Air Conditioner (AC) with an inbuilt Ultrasonic Device (AC-UD) was mounted on the wall of the test chamber while the control chamber was without the (AC-UD). In order to determine the expel rate due to the ultrasonic device, 50 sucrose fed female mosquitoes were introduced into the test chamber with ACUD. The rates at which the mosquitoes migrated to the adjacent chamber without AC-UD were recorded hourly for six hours and at 24 hours. In a separate experiment, the knockdown rate was determined by introducing 50-sucrose fed female mosquitoes into a test chamber with AC-UD and the windows properly locked. Knock down was recorded hourly for the first six hours, and subsequently at 24 hours post exposure by counting the number of mosquitoes on the ground. The tests were carried out on the basis of switching “ON” and “OFF” of the AC’s fan and ultrasonic device to indicate the associated effects of the variables of interest. For the knockdown tests, the final mortality at 24 hours recorded was 60.7%, 15.3% and 17.3% for experiments “fan ON + ultrasonic ON”, “fan ON + ultrasonic OFF”, and “fan OFF + ultrasonic ON” respectively. The final mortality recorded for the control at 24 hours was 4.7%. For the expel tests, the experiment “fan ON + ultrasonic ON” had the highest proportion of mosquitoes expelled (62.7%) after 24 hours, while mosquitoes not expelled were knocked down (28.0%). This was followed by “fan OFF + ultrasonic ON” with expel of 26.0% and only 14% knockdown. For “fan ON + ultrasonic OFF” the expelled mosquitoes was 13.3% with only 1.3% knockdown after 24 hours. The expel rate for the control was 1.3% after 24 hours while 2.0% was knocked down after 24 hours. The combination of the ultrasonic device and fan on was relatively more effective in knocking down and/or expelling Anopheles gambiae. This suggests that the ultrasonic device in combination with the fan implanted in the AC is effective for personal protection against mosquitoes.