Larvicidal Activity of Two Cymbopogon Species Leaf Extracts and Essential Oils against Anopheles gambiae Gilles (Diptera: Culicidae)

Abstract

Aims: The present investigation aimed to assess the toxic effect of hexane, acetone and methanol extracts of Cymbopogon citratus and Cymbopogon giganteus against 3rd and 4th instar of Anopheles gambiae larvae under laboratory conditions. Place and Duration of Study: Plant products were extracted from November 2017 to February 2018 in the Chemistry laboratory, while the larvicidal tests were conducted from April to June 2018 in the laboratory of Applied Zoology of the Faculty of Science, University of Ngaoundere, Cameroon. Methodology: Twenty five (25) 3rd and 4th instars of An. gambiae were subjected to methanol, acetone and methanol plant extracts of the two plants at doses of 1000, 500, 250 and 125 mg/L each while their essential oils were tested at concentrations of 200, 100, 50 and 25 mg/L. Dichlovos tested at the recommended dose of 1000 mg/L was performed as positive control while 1mL of tween-80 in 99 mL of natural breeding site water was used as negative control. Larval mortality was recorded after 24 h post treatment for plant extracts and after 1, 6, 12, 18 and 24 h post-exposure for plant essential oils. Results: At the highest concentration of 1000 mg/L, C. citratus extract caused 100% mortality of mosquito larvae while 84, 81 and 88% mortality of larvae were recorded with hexane, acetone and methanol leaf extract of C. giganteus, respectively. C. citratus (LC50=58.32 mg/L) and C. giganteus (LC50=372.36 mg/L) hexane extracts were more potent than acetone and methanol extracts of the plants. C. citratus extracts were the most effective against larvae compared to C. giganteus extracts. Essential oil of C. citratus (LC50=27.98 mg/L after 1h) was also the most toxic on mosquito larvae compared to C. giganteus (LC50=180.07 mg/L after 1h) essential oil. Conclusion: C. citratus plant and specially its hexane extract and essential oil could be taken into consideration as a new source of botanical insecticide and may be used in the mosquito control programs for An. gambiae larvae elimination in their breeding sites.