Multi-insecticide resistant malaria vectors in the field remain susceptible to malathion, despite the presence of Ace1 point mutations

Abstract

Insecticide resistance in Anopheles mosquitoes is seriously threatening the success of insecticide-based malaria vector control. Surveillance of insecticide resistance in mosquito populations and identifying the underlying mechanisms enables optimisation of vector control strategies. Here, we investigated the molecular mechanisms of insecticide resistance in three Anopheles coluzzii field populations from southern Côte d’Ivoire, including Agboville, Dabou and Tiassalé. All three populations were resistant to bendiocarb, deltamethrin and DDT, but not or only very weakly resistant to malathion. The absence of malathion resistance is an unexpected result because we found the acetylcholinesterase mutation Ace1-G280S at high frequencies, which would typically confer cross-resistance to carbamates and organophosphates, including malathion. Notably, Tiassalé was the most susceptible population to malathion while being the most resistant one to the pyrethroid deltamethrin. The resistance ratio to deltamethrin between Tiassalé and the laboratory reference colony was 1,800 fold. By sequencing the transcriptome of individual mosquitoes, we found numerous cytochrome P450-dependent monooxygenases – including CYP6M2, CYP6P2, CYP6P3, CYP6P4 and CYP6P5 – overexpressed in all three field populations. This could be an indication for negative cross-resistance caused by overexpression of pyrethroid-detoxifying cytochrome P450s that may activate pro-insecticides, thereby increasing malathion susceptibility. In addition to the P450s, we found several overexpressed carboxylesterases, glutathione S-transferases and other candidates putatively involved in insecticide resistance.

Species composition and insecticide resistance in malaria vectors in Ellibou, southern Côte d’Ivoire and first finding of Anopheles arabiensis in Côte d’Ivoire

“…All qPCR reactions, including the species identification, target-site and metabolic resistance assays, were performed on a Bio-Rad CFX 96 real-time PCR machine (Bio-Rad; Hercules, CA, USA). In each reaction, 1 µl of the nucleic acids extract from individual mosquitoes was added to the one-step reverse transcription qPCR (RT-qPCR) master mix supplied by Fast Track Diagnostics (Esch-sur-Alzette, Luxembourg) together with the primers and probes at the concentrations described by Wipf et al [30] to reach a total reaction volume of 10 µl. The following thermal cycle conditions were used for all assays: 50 °C for 15 min, 95 °C for 3 min, followed by 40 amplification cycles of 95 °C for 3 s and 60 °C for 30 s. The purified nucleic acids were subjected to two complementary TaqMan qPCR assays to identify the 141 specimens to species level within the An.…”

“…The following thermal cycle conditions were used for all assays: 50 °C for 15 min, 95 °C for 3 min, followed by 40 amplification cycles of 95 °C for 3 s and 60 °C for 30 s. The purified nucleic acids were subjected to two complementary TaqMan qPCR assays to identify the 141 specimens to species level within the An. gambiae complex with previously described adaptations to the original protocols put forth by Wipf et al [30].…”

Small-scale field evaluation of PermaNet® Dual (a long-lasting net coated with a mixture of chlorfenapyr and deltamethrin) against pyrethroid-resistant Anopheles gambiae mosquitoes from Tiassalé, Côte d’Ivoire

“…Several studies have shown a wide spread resistance in local Anopheles to most of the insecticide classes currently used in malaria vector control (e.g. pyrethroids, DDT and carbamates) [5][6][7][8]. The existence of multiple mechanisms of resistance in the main vector, Anopheles gambiae sensu lato (s.l.)…”

First detection of resistance to deltamethrin in Spanish populations of the Mediterranean fruit fly, Ceratitis capitata

“…On the contrary, deltamethrin-resistant strains were susceptible to spinosad by ingestion and the spinosadresistant strain JW-100 s was susceptible to deltamethrin, indicating that spinosad is a good candidate for spray, when needed, in fields where bait stations with deltamethrin are deployed. Interestingly, negative cross-resistance between pyrethroid resistance mediated by P450 and organophosphates has been reported in mosquitoes (Wipf et al 2022). However, the only organophosphate approved for Medfly control in citrus crops in Spain is phosmet, whose use is very limited.…”