Impacts of dual active-ingredient bed nets on the behavioural responses of pyrethroid resistant Anopheles gambiae determined by room-scale infrared video tracking

Abstract

Background The success of insecticide treated bed nets (ITNs) for malaria vector control in Africa relies on the behaviour of various species of Anopheles. Previous research has described mosquito behavioural alterations resulting from widespread ITN coverage, which could result in a decrease in net efficacy. Here, behaviours were compared including timings of net contact, willingness to refeed and longevity post-exposure to two next-generation nets, PermaNet® 3.0 (P3 net) and Interceptor® G2 (IG2 net) in comparison with a standard pyrethroid-only net (Olyset Net™ (OL net)) and an untreated net. Methods Susceptible and resistant Anopheles gambiae mosquitoes were exposed to the nets with a human volunteer host in a room-scale assay. Mosquito movements were tracked for 2 h using an infrared video system, collecting flight trajectory, spatial position and net contact data. Post-assay, mosquitoes were monitored for a range of sublethal insecticide effects. Results Mosquito net contact was focused predominantly on the roof for all four bed nets. A steep decay in activity was observed for both susceptible strains when P3 net and OL net were present and with IG2 net for one of the two susceptible strains. Total mosquito activity was higher around untreated nets than ITNs. There was no difference in total activity, the number, or duration, of net contact, between any mosquito strain, with similar behaviours recorded in susceptible and resistant strains at all ITNs. OL net, P3 net and IG2 net all killed over 90% of susceptible mosquitoes 24 h after exposure, but this effect was not seen with resistant mosquitoes where mortality ranged from 16 to 72%. All treated nets reduced the willingness of resistant strains to re-feed when offered blood 1-h post-exposure, with a more pronounced effect seen with P3 net and OL net than IG2 net. Conclusion These are the first results to provide an in-depth description of the behaviour of susceptible and resistant Anopheles gambiae strains around next-generation bed nets using a room-scale tracking system to capture multiple behaviours. These results indicate that there is no major difference in behavioural responses between mosquito strains of differing pyrethroid susceptibility when exposed to these new ITNs under the experimental conditions used.

3D video tracking analysis reveals that mosquitoes pass more likely through holes in permethrin-treated than in untreated nets

“…A recent room-scale infrared video tracking study in An. gambiae s.l., testing the same net as here, also failed to find a repellent effect 51 . Similarly, when using video tracking analysis of An.…”

Insecticides Resistance Profiles of Anopheles Mosquito From Rural and Peri-Urban Communities of Gombe State, North East, Nigeria

“…from Ghana in the presence of pyrethroid resistant after LLINs mass distribution campaign. However, recent studies revealed less performance of deltamethrin-PBO net in Tanzania and Benin when compared with chorofenapyr Nets (Gleave et al, 2023). Although, non-PBO net provide protection against malaria vector; Pyrethroid-PBO performed better in enhancing less parasite prevalence via reduction in mosquito blood feeding rate and increase high mosquito mortality.…”

Insecticidal roof barriers mounted on untreated bed nets can be as effective against Anopheles gambiae as regular insecticide-treated bed nets

“…Sufficient knowledge of the entomological mode of action of ITNs already exists to enable us to identify the location of regions of the net where a number of important vector mosquito species are most likely to arrive 19 – 21 and where the insecticide is best positioned to maximise contact with mosquitoes 11 , the areas most vulnerable to physical damage that would benefit from tougher net fibre, and areas that are rarely visited by mosquitoes. Recent research suggests that most bed nets, including the new bi-treated nets, have similar entomological modes of action 22 . Can this range of knowledge not be used to design better bed nets, durable ITNs that are optimised to kill mosquitoes and prevent malaria transmission in rural Africa, rather than simply the cheapest designed products that tick the boxes required to complete a WHO form?…”