No abstract

Constant assessment of insecticide resistance levels is mandatory to implement adequate malaria control tools, but little information is available on the annual dynamics of resistance. We, therefore, monitored variations in resistance in Anopheles gambiae s.l. over four seasons during 2 years in two localities of Yaoundé: urban Etoa-Meki and peri-urban Nkolondom. Mosquitoes were collected seasonally at larval stage and reared to adults for insecticide susceptibility tests and molecular analysis of resistance mechanisms. Anopheles coluzzii was found in Etoa-Meki and An. gambiae in Nkolondom. Low mortalities to pyrethroids were observed (permethrin <10%, deltamethrin <21%), and resistance extended to 5Â and 10Â diagnostic doses, revealing a marked increase compared to previous studies. A seasonal variation in resistance was observed with the highest levels within dry seasons in Etoa-Meki and rainy seasons in Nkolondom. The 1014F kdr allele shows a high frequency (0.9), associated with overexpression of metabolic genes (Cyp6M2, Cyp6P4, Cyp9K1, Cyp6Z1, and Cyp6Z2) varying significantly seasonally. This study reveals an escalation in resistance to pyrethroids in Yaoundé's malaria vectors with seasonal variations. An adequate choice of the implementation period of punctual vector control actions according to the resistance profile will help to potentiate the desired effect and thus improve its efficiency.

The impact of mirid true bugs on cocoa production is widely assessed for Sahlbergella singularis and Distantiella theobroma species in the cocoa growing area in Africa. No study has been focused on the impact of another common mirid species in cocoa farming, such as Helopeltis sp., on the cocoa productivity. Thus, the main objective of this work was to assess the effect of Helopeltis sp. attacks on cocoa productivity of ten genotypes. Observations were made on infested fruits (cherelles, immature and mature fruits) under a randomized experimental field design. A control assay was also used in our investigations. The overall results revealed that only fruits infected by mirids aborted: 80.0% for cherelles and 0.4% for immature fruits. The numbers of aborted fruits were statistically comparable between cocoa genotypes and their rates varied from 60 to 96%. In contrast, ANOVA showed that the feeding lethal punctures of Helopeltis sp. were significantly (p<5%) different between fruits of the tested cocoa genotypes; the mean values ranged from 41.5±5.5 to 76.0±4.6 and were classified in three homogenous groups, with a significant sensitivity of clone/hybrids T79/501, UPA143 x SNK64 and T79/501 x SNK413 compared with clone SNK16. The proposal of including Helopeltis sp. as one of the most important pest in cacaoculture is discussed.

Background Cameroon is considering the implementation of indoor residual spraying (IRS) as a complementary measure to control malaria in the context of high pyrethroid resistance in major malaria vectors. Non-pyrethroid insecticide classes such as organophosphates and carbamates may be utilized in IRS due to widespread pyrethroid resistance. However, the success of this strategy depends on good knowledge of the resistance status of malaria vectors to carbamates and organophosphates. Here, we assessed the susceptibility profile of Anopheles gambiae sensu lato with respect to carbamates and organophosphate and the distribution of the molecular mechanism underlying resistance to these insecticides. Methods Anopheles gambiae s.l. mosquitoes were collected from nine settings across the country and bio-assayed with bendiocarb, propoxur and pirimiphos-methyl. The Ace-1 target-site G119S mutation was genotyped using a TaqMan assay. To investigate the polymorphism in the Ace-1 gene, a region of 924 base pairs in a sequence of the gene was amplified from both live and dead females of An. gambiae exposed to bendiocarb. Results Pirimiphos-methyl induced full mortality in An. gambiae s.l. from all study sites, whereas for carbamates, resistance was observed in four localities, with the lowest mortality rate recorded in Mangoum (17.78 ± 5.02% for bendiocarb and 18.61 ± 3.86% for propoxur) in the southern part of Cameroon. Anopheles coluzzii was found to be the predominant species in the northern tropical part of the country where it is sympatric with Anopheles arabiensis. In the localities situated in southern equatorial regions, this species was predominant in urban settings, while An. gambiae was the most abundant species in rural areas. The G119S Ace-1 target-site mutation was detected only in An. gambiae and only in the sites located in southern Cameroon. Phylogenetic analyses showed a clustering according to the phenotype. Conclusion The occurrence of the Ace-1 target-site substitution G119S in An. gambiae s.l. populations highlights the challenge associated with the impending deployment of IRS in Cameroon using carbamates or organophosphates. It is therefore important to think about a resistance management plan including the use of other insecticide classes such as neonicotinoids or pyrrole to guarantee the implementation of IRS in Cameroon. Graphical Abstract