3D video tracking analysis reveals that mosquitoes pass more successfully through holes of a permethrin-treated than an untreated net

Abstract

Abstract In addition to killing, mosquito nets treated with permethrin have been claimed to repel mosquitoes, reducing their success in passing through a holed net. We have tested this hypothesis by tracking mosquitoes in a modified World Health Organization tunnel test. In the original assay, mosquitoes are released at one end of the tunnel and have to pass through a holed piece of net to reach the bait at the other end while mortality and feeding rates are recorded upon exposure. Since the original test does not reveal how mosquitoes move within the tunnel, we combined the assay with a 3D infrared video camera system. We tracked susceptible and permethrin-resistant Anopheles gambiae s.s. as they moved in the tunnel and interacted with an untreated or a permethrin-treated net. Surprisingly, while permethrin increased the mortality and reduced the blood-feeding rates, twice as many mosquitoes passed through the holes of the permethrin-treated net. The 3D flight trajectories reveal that upon exposure to a permethrin-treated net, both insecticide susceptible and resistant An. gambiae s.s. show an increased contact-disengagement or ‘excitation’, thereby augmenting their chance of getting through the holes in the net. The study underlines the complexity of behavioural mode of actions of insecticides.