Everyone who ever went out of bed at night to swat mosquitoes knows: this is a difficult task. Scientists of Wageningen University & Research used high-speed cameras and a mechanical swatter to study the escape performance of two mosquito species: the malaria mosquito and yellow fever mosquito. Among more than ten thousand attacks, only eight per cent led to a collision between the mosquito and the swatter.
The high escape performance was surprising to the researchers, but even more surprising was that the night-active malaria mosquito escaped more successfully in pitch darkness than in day-light. ‘We think that mosquitoes use visual clues to detect incoming attacks’, says researcher Antoine Cribellier of the Experimental Zoology chairgroup. ‘But in the complete dark, these visual clues are, of course, not present. It is possible that the airflow of the attacker simply sweeps the animal, but that would be the same during day and night’.
Unpredictable flight path
The answer to this surprising result came when Cribellier analysed the flight behaviour of mosquitoes prior to the attack. Malaria mosquitoes continuously exhibit an unpredictable flight path when flying in the dark. This variable and erratic flight behaviour prevents the predator or host such as a human from accurately predicting the flying mosquito’s position.
While the night-active malaria mosquito relies on its unpredictable flight behaviour, the day-active yellow fever mosquito shows, as expected, an increased escape performance during day-light. Simply put, it is easier to detect danger in bright light, and thus, escape manoeuvres in day-light are quicker. Jeroen Spitzen of the Laboratorium of Entomology: ‘This shows that both species have adjusted their flight behaviour to maximise their escape performance in their natural blood-feeding light conditions when the defensive actions by their hosts are most frequent.’
Vectors of deadly human diseases
This research published in Current Biology also has important practical implications. Both studied mosquito species have a strong preference for human hosts and are major vectors of several deadly human diseases, such as malaria, yellow fever, Zika and dengue. Therefore, the results of this research can be used to optimise existing or develop new mosquito trapping systems.
‘Not only the outcome of this research is remarkable’, says Florian Muijres, ‘the technique used to study the escape performance is spectacular as well’. The researchers used five high-speed cameras to track flying mosquitoes in real-time. Based on the real-time position and velocity of the mosquito, the mechanical swatter was automatically triggered to simulate the attack of a human hand. This high-tech method was crucial for discovering how day- and night-active mosquitoes avoid being swatted when trying to bite you.