Identification and Larvicidal Efficacy of Mosquito-Repelling Plants Used in Malaria Vector Control in South-East Benin

After identifying issues posed by some synthetic insecticides, the scientific community is now looking for other natural products with insecticidal and/or insect repellent characteristics. This study aimed to identify the plants of the Beninese flora known for their insecticidal and/or insect repellent effects and the indigenous techniques of their use and to evaluate the combined efficacy of extracts of a few on mosquito larvae for the control of malaria vectors in the South-East of Benin. A survey was conducted and the insecticidal effects of three combinations made from Azadirachta indica, Cymbopogon nardus and Hyptis suaveolens oils on Anopheles gambiae larvae were studied. The data were analyzed using R software, and Chi-square test was used to compare death rates. Twelve (12) plant species were identified. The combinations of C. nardus and H. suaveolens oils induced the highest mortality rates (90 ± 4.15% and 68 ± 9.14% with stages 2 and 3 larvae, respectively). The application of extracts from these plants to control the malaria vectors population would reduce the use of chemical pesticides, hence the need to promote and enhance the formulations of biopesticides based on plant extracts. Keywords:    Plant species, biopesticides, mosquito-repelling plants, vectors. &nbsp

Pre-intervention characteristics of the mosquito species in Benin in preparation for a randomized controlled trial assessing the efficacy of dual active-ingredient long-lasting insecticidal nets for controlling insecticide-resistant malaria vectors.

BACKGROUND: This study provides detailed characteristics of vector populations in preparation for a three-arm cluster randomized controlled trial (RCT) aiming to compare the community impact of dual active-ingredient (AI) long-lasting insecticidal nets (LLINs) that combine two novel insecticide classes-chlorfenapyr or pyriproxifen-with alpha-cypermethrin to improve the prevention of malaria transmitted by insecticide-resistant vectors compared to standard pyrethroid LLINs. METHODS: The study was carried out in 60 villages across Cove, Zangnanando and Ouinhi districts, southern Benin. Mosquito collections were performed using human landing catches (HLCs). After morphological identification, a sub-sample of Anopheles gambiae s.l. were dissected for parity, analyzed by PCR for species and presence of L1014F kdr mutation and by ELISA-CSP to identify Plasmodium falciparum sporozoite infection. WHO susceptibility tube tests were performed by exposing adult An. gambiae s.l., collected as larvae from each district, to 0.05% alphacypermethrin, 0.75% permethrin, 0.1% bendiocarb and 0.25% pirimiphos-methyl. Synergist assays were also conducted with exposure first to 4% PBO followed by alpha-cypermethrin. RESULTS: An. gambiae s.l. (n = 10807) was the main malaria vector complex found followed by Anopheles funestus s.l. (n = 397) and Anopheles nili (n = 82). An. gambiae s.l. was comprised of An. coluzzii (53.9%) and An. gambiae s.s. (46.1%), both displaying a frequency of the L1014F kdr mutation >80%. Although more than 80% of people slept under standard LLIN, human biting rate (HBR) in An. gambiae s.l. was higher indoors [26.5 bite/person/night (95% CI: 25.2-27.9)] than outdoors [18.5 b/p/n (95% CI: 17.4-19.6)], as were the trends for sporozoite rate (SR) [2.9% (95% CI: 1.7-4.8) vs 1.8% (95% CI: 0.6-3.8)] and entomological inoculation rate (EIR) [21.6 infected bites/person/month (95% CI: 20.4-22.8) vs 5.4 (95% CI: 4.8-6.0)]. Parous rate was 81.6% (95%CI: 75.4-88.4). An. gambiae s.l. was resistant to alpha-cypermethrin and permethrin but, fully susceptible to bendiocarb and pirimiphos-methyl. PBO pre-exposure followed by alpha-cypermethrin treatment induced a higher 24 hours mortality compared to alphacypermethrin alone but not exceeding 40%. CONCLUSIONS: Despite a high usage of standard pyrethroid LLINs, the study area is characterized by intense malaria transmission. The main vectors An. coluzzii and An. gambiae s.s. were both highly resistant to pyrethroids and displayed multiple resistance mechanisms, L1014F kdr mutation and mixed function oxidases. These conditions of the study area make it an appropriate site to conduct the trial that aims to assess the effect of novel dual-AI LLINs on malaria transmitted by insecticide-resistant vectors

Additional file 1 of First report of natural infection of Anopheles gambiae s.s. and Anopheles coluzzii by Wolbachia and Microsporidia in Benin: a cross-sectional study

Additional file 1: Table S1. Mosquito species composition (PSC data). Table S2. Infection prevalence with Wolbachia Anga and Microsporidia MB per molecular species (An. gambiae s.s. and An. coluzzii) in each study commune (HLC + PSC data). Table S3. SR per molecular species, in each study commune (HLC + PSC data)