Despite the highest global burden of malaria, information on bionomics and insecticide resistance status of malaria vectors is grossly lacking in the densely populated Sahelo-Sudanian region of Nigeria. To support evidence-based vector control we characterised transmission and resistance profiles ofAnopheles coluzziipopulations from three sites in northern Nigeria. High sporozoite infection (~19.51%) was found in theAn.coluzziipopulations. A high pyrethroid resistance was observed with only 1% mortality against deltamethrin, a high LD₅₀(96.57 µg/ml), and a high LT₅₀(170.27 min, resistance ratio of ~51 compared with the fully susceptible Ngoussou colony). Moderate carbamate resistance was observed. Synergist bioassays significantly recovered deltamethrin susceptibility implicating CYP450s (mortality = 85%, χ² = 134.04, p < 0.0001) and esterases (mortality = 56%, χ² = 47.31, p < 0.0001). Reduced bed net efficacy was also observed, with mortalities on exposure to the roof of PermaNet3.0 (PBO + deltamethrin) more than 22 times compared to the side panel (deltamethrin). TaqMan genotyping revealed a high frequency of 1014Fkdrmutation (82%) with significant difference in genotype distribution associated with permethrin resistance [OR = 4.69 (CI:1.53–14.35, χ² = 8.22 p = 0.004]. Sequencing of exons 18–21 of the VGSC led to detection of two additional nonsynonymous mutations, Ile10148Asn and Ser1156Gly. These findings highlight the threats posed by the highly resistantAn.coluzziito malaria control in Nigeria.

To support evidence-based control measures, two Nigerian Aedes populations (BUK and Pantami) were characterised. Larval bioassay using temephos and deltamethrin revealed a significant increase in deltamethrin resistance, with LC₅₀ of 0.018mg/L (resistance ratio compared to New Orleans, RR = 2.250) in 2018 increasing ~6-fold, by 2019 (LC₅₀ = 0.100mg/L, RR = 12.5), and ~11-fold in 2020 (LC₅₀ = 0.198mg/L, RR = 24.750). For the median deltamethrin concentration (0.05mg/L), a gradual decrease in mortality was observed, from 50.6% in 2018, to 44.9% in 2019, and 34.2% in 2020. Extremely high DDT resistance was observed, with <3% mortalities and LT₅₀s of 352.87 min, 369.19 min and 406.94 min in 2018, 2019 and 2020, respectively. Significant temporal increase in resistance was observed towards ƛ-cyhalothrin (a type II pyrethroid) over three years. Synergist bioassays with diethylmaleate and piperonylbutoxide significantly recovered DDT and ƛ-cyhalothrin susceptibility respectively, implicating glutathione S-transferases and CYP450s. Cone bioassays revealed increased resistance to the PermaNet^® 3.0, side panels (mortalities of 94% in 2018, 66.4% in 2019, and 73.6% in 2020), while full susceptibility was obtained with the roof of PermaNet^® 3.0. The F1534C kdr mutation occurred in low frequency, with significant correlation between heterozygote genotypes and DDT resistance. This temporal increase in resistance is a major challenge for control of this vector of public health importance.

Suspicion of failure in the effectiveness of artemisinin-based combination therapies (currently the first-line treatment of malaria, worldwide) is leading to the unofficial use of alternative antimalarials, including chloroquine and sulfadoxine/pyrimethamine, across northern Nigeria. To facilitate evidence-based resistance management, antimalarial resistance mutations were investigated in Plasmodium falciparum multidrug resistance-1 (pfmdr1) and chloroquine resistance transporter (pfcrt), in isolates from Kano, northwestern Nigeria. Out of the 88 samples genotyped for pfmdr1 N86Y mutation using PCR/restriction fragment length polymorphism, one sample contained the 86Y mutation (86Y_frequency = 1.14%). The analysis of 610 bp fragments of pfmdr1 from 16 isolates revealed two polymorphic sites and low haplotype diversity (H_d = 0.492), with only 86 Y mutations in one isolate, and 184 F replacements in five isolates (184F_frequency = 31.25%). The analysis of 267 bp fragments of pfcrt isolates revealed high polymorphism (H_d = 0.719), with six haplotypes and seven non-synonymous polymorphic sites. Eleven isolates (61.11%) were chloroquine-resistant, CQR (C₇₂V₇₃I₇₄E₇₅T₇₆ haplotype), two of which had an additional mutation, D⁵⁷E. An additional sequence was CQR, but of the C₇₂V₇₃M₇₄E₇₅T₇₆ haplotype, while the rest of the sequences (33.33%) were chloroquine susceptible (C₇₂V₇₃M₇₄N₇₅K₇₆ haplotype). The findings of these well characterized resistance markers should be considered when designing resistance management strategies in the northwestern Nigeria.

Malaria control relies on first-line treatments that use artemisinin-combination therapies (ACT). Unfortunately, mutations in the plasmodium falciparum kelch13 gene result in delayed parasite clearance. Research on what is causing ACT failure is non-existent in northwestern Nigeria. Thus, the presence of mutations in kelch13 in P. falciparum isolates from Kano, Nigeria was investigated in this study. Microscopic examination of 154 blood samples obtained from patients revealed a high prevalence of P. falciparum infection (114 positive individuals, slide positivity rate = 74.03%). The 114 patients were administered Cartef^® (ACT) and out of the 50 patients that returned for the 14-day follow up, 11 were positive for P. falciparum (slide positivity rate = 22%). On day 0, 80 samples out of 114 and 11 samples on day 14 (91 out of 125 microscopy-positive samples) were positive with Plasmodium according to the PCR of cytochrome oxidase I, which corresponds to 72.8%. A fragment of the kelch13 gene encompassing the propeller domains was sequenced in 49 samples, alongside samples of the susceptible strain pf_3D7. Low polymorphism was observed, suggesting a lack of selection on this gene, and only six mutations (Glu⁴³³Gly, Phe⁴³⁴Ile, Phe⁴³⁴Ser, Ile⁶⁸⁴Asn, Ile⁶⁸⁴Thr and Glu⁶⁸⁸Lys) were found. The epidemiologic impact of these mutations and their potential role in ACT resistance needs to be investigated further.

In 2016, northern Nigeria experienced a devastating infestation by the tomato leaf miner, leading to soaring in prices of tomatoes across the country. Unfortunately, information on the resistance status of this pest is lacking in northern Nigeria, hampering appropriate control measures. Here, we identified to species level and, using bioassays, characterised insecticide susceptibility profile of a field population of a tomato leaf miner from northern Nigeria. Highest resistance was observed with λ-cyhalothrin (a Type II pyrethroid) with a low mortality (18.52% at 56 h) and LD₅₀ of 7461.474 ppm. Resistance was also established toward propoxur and chlorpyrifos-methyl with average mortalities each of 56% and LD_50s of 1023.51 ppm and 106.351 ppm, respectively. Highest susceptibility was observed from abamectin with mortality of 86% and LD₅₀ of 0.034 ppm. Pre-exposure to the synergist piperonylbutoxide significantly recovered λ–cyhalothrin susceptibility ((mortality~90%, χ² = 98.35, p < 0.0001) and LD₅₀ = 0.92 ppm) implicating P450 monoxygenases. No significant changes were observed on pre-exposure to diethyl maleate and triphenylphosphate-inhibitors of glutathione S-transferases and carboxylesterases, respectively. Sequencing of domain II of the voltage-gated sodium channel established 1014F kdr mutation 100% fixed in both λ-cyhalothrin-alive and dead larvae. These findings highlight the challenges for control of this invasive agricultural pest in northern Nigeria.

The Nigerian Government is scaling up the distribution of insecticide-treated bed nets for malaria control, but the lack of surveillance data, especially in the Sudan/Sahel region of the country, may hinder targeting priority populations. Here, the vectorial role and insecticide resistance profile of a population of a major malaria vector Anopheles funestus sensu stricto from Sahel of Nigeria was characterised. An. funestus s.s. was the only vector found, with a high human blood index (100%) and a biting rate of 5.3/person/night. High Plasmodium falciparum infection was discovered (sporozoite rate = 54.55%). The population is resistant to permethrin (mortality = 48.30%, LT₅₀ = 65.76 min), deltamethrin, DDT (dichlorodiphenyltrichloroethane) and bendiocarb, with mortalities of 29.44%, 56.34% and 54.05%, respectively. Cone-bioassays established loss of efficacy of the pyrethroid-only long-lasting insecticidal nets (LLINs); but 100% recovery of susceptibility was obtained for piperonylbutoxide (PBO)-containing PermaNet^®3.0. Synergist bioassays with PBO and diethyl maleate recovered susceptibility, implicating CYP450s (permethrin mortality = 78.73%, χ² = 22.33, P < 0.0001) and GSTs (DDT mortality = 81.44%, χ² = 19.12, P < 0.0001). A high frequency of 119F GSTe2 mutation (0.84) was observed (OR = 16, χ² = 3.40, P = 0.05), suggesting the preeminent role of metabolic resistance. These findings highlight challenges associated with deployment of LLINs and indoor residual spraying (IRS) in Nigeria.