title: Methanolic extract of Agerantum conyzoides exhibited toxicity and growth disruption activities against Anopheles gambiae sensu stricto and Anopheles arabiensis larvae.
abstract: BACKGROUND
  Vector control remains the mainstay to effective malaria management. The negative implications following persistent application of synthetic insecticides geared towards regulation of mosquito populations have necessitated prospection for ecofriendly effective chemistries. Plant-derived compounds have the potential to control malaria-transmitting mosquito populations. Previously, Agerantum conyzoides extracts have demonstrated toxicity effects on disease-transmitting mosquitoes. However, their efficacy in controlling Afrotropical malaria vectors remains unclear. Herein, the toxicity and growth disruption activities of crude methanolic leaf extract of A. conyzoides on Anopheles gambiae sensu stricto and An. arabiensis larvae were assessed.
  
  
  METHODS
  Late third (L3) instars of An. gambiae s.s and An. arabiensis larvae were challenged with increasing doses of crude methanolic extract of A. conyzoides. The larval mortality rates were recorded every 24 h and the LC50values determined at their associated 95% confidence levels. ANOVA followed by Post-hoc Student-Newman-Keuls (SNK) test was used to compare results between treatment and control groups. Phytochemical profiling of the extract was performed using standard chemical procedures.
  
  
  RESULTS
  Treatment of larvae with the methanolic extract depicted dose-dependent effects with highest mortality percentages of ≥ 69% observed when exposed with 250 ppm and 500 ppm for 48 h while growth disruption effects were induced by sublethal doses of between 50-100 ppm for both species. Relative to experimental controls, the extract significantly reduced larval survival in both mosquito species (ANOVA, F(8,126)= 43.16776, P < 0.001). The LC50values of the extract against An. gambiae s.s ranged between 84.71-232.70 ppm (95% CI 81.17-239.20), while against An. arabiensis the values ranged between 133.46-406.35 ppm (95% CI 131.51-411.25). The development of the juvenile stages was arrested at pupal-larval intermediates and adult emergence. The presence of alkaloids, aglycone flavonoids, triterpenoids, tannins and coumarins can partly be associated with the observed effects.
  
  
  CONCLUSIONS
  The extract displayed considerable larvicidal activity and inhibited emergence of adult mosquitoes relative to experimental controls, a phenomenon probably associated with induced developmental hormone imbalance. Optimization of the bioactive compounds could open pathways into vector control programmes for improved mosquito control and reduced malaria transmission rates.
authors.affiliation: Department of Biochemistry, Jomo Kenyatta University of Agriculture and Technology, P.O. Box 62000-00200, Nairobi, Kenya. Jackson_mbithi@yahoo.com.
authors.forename: Jackson Mbithi
authors.initials: JM
authors.lastname: Muema
authors.affiliation: Department of Medicine, Kisii University, P.O. Box 408-40200, Kisii, Kenya.
authors.forename: Sospeter Ngoci
authors.initials: SN
authors.lastname: Njeru
authors.affiliation: École Supérieure d'Agricultures Institute, 55, Rue Rabelais, B.P 30748 49007, Angers Loire, France.
authors.forename: Céline
authors.initials: C
authors.lastname: Colombier
authors.affiliation: International Centre of Insect Physiology and Ecology, P.O. Box 30772-00100, Nairobi, Kenya.
authors.forename: Rose Muthoni
authors.initials: RM
authors.lastname: Marubu
mesh_terms: D000818:Animals; D000852:Anopheles / Q000187:drug effects* / Q000254:growth & development; D019659:Asteraceae / Q000737:chemistry*; D007306:Insecticides; D007814:Larva / Q000187:drug effects / Q000254:growth & development
chemical_list: D007306:Insecticides
keywords: Agerantum conyzoides; Anopheles arabiensis; Anopheles gambiae s.s; Growth disruption; Larvicidal activity; Malaria; Vector control