Effects of oil extracts of Cyperus papyrus L. and Typha latifolia L. on survival of larvae of the malaria mosquito, Anopheles arabiensis patton

Abstract

Around Lake Tana, larvae of the malaria mosquito Anopheles arabiensis Patton were rare to be found in lakeshore breeding habitats with Cyperus papyrus L. and could only be recovered with low probability from breeding habitats with Typha latifolia L. This study aimed to investigate oil contents of the grasses and effect of natural oils extracted from rhizome and aerial parts of these grasses on the survival of An. arabiensis mosquito larvae under laboratory conditions. Samples of C. papyrus and T. latifolia were collected from different mosquito breeding habitats along the shoreline of Lake Tana, northwest Ethiopia. Natural oils from rhizome and aerial parts of these grass species were extracted with n-hexane using Soxhlet extractor apparatus and their contents were quantified. Different doses of the oil extracts were dissolved in ethanol and were tested to determine their toxicity to laboratory reared 4th stage larvae of An. arabiensis. The rhizome of Cyperus papyrus has significantly higher oil content (2.09 ± 0.23) than that of T. latifolia (1.455 ± 0.011) (P<0.05). The toxicity of the oil extracts from both T. latifolia and C. papyrus grasses increased in a dose dependent manner to cause significant larval mortality on An. arabiensis. Accordingly, the present study confirmed that the rhizome of C. papyrus has substantial amount of natural oils that makes this grass species as a candidate to reduce populations of An. arabiensis in the area. The effect of natural oils from these grass species in regulating mosquito populations in potential breeding habitats need to be further evaluated. The ecological significance of the high amount of natural oil production by rhizome of C. papyrus in breeding habitats needs to be studied.