Evaluations of larvicidal activity of medicinal plant extracts to Aedes aegypti (Diptera: Culicidae) and other effects on a non target fish

摘要

A preliminary study was conducted to investigate the effects of the extracts of 112 medicinal plant species, collected from the southern part of Thailand, on Aedes aegypti. Studies on larvicidal properties of plant extracts against the fourth instar larvae revealed that extracts of 14 species showed evidence of larvicidal activity. Eight out of the 14 plant species showed 100% mosquito larvae mortality. The LC_(50) values were less than 100 mu g/mL (4.1 mu g/ mL—89.4 mu g/mL). Six plant species werecomparatively more effective against the fourth instar larvae at very low concentrations. These extracts demonstrated no or very low toxicity to guppy fish (Poecilia reticulata), which was selected to represent most common non-target organism found in habitats of Ae. aegypti, at concentrations active to mosquito larvae. Three medicinal plants with promising larvicidal activity, having LC_(50) and LC_(90) values being 4.1 and 16.4 mu g/mL for Mammea siamensis, 20.2 and 34.7 mu g/mL for Anethum graveolens and 67.4 and 110.3 mu g/mL for Annona muricata, respectively, were used to study the impact of the extracts on the life cycle of Ae. aegypti. These plants affected pupal and adult mortality 'and also affected the reproductive potential of surviving adults by reducing the number of eggs laid and the percentage of egg hatchability. When each larval stage was treated with successive extracts at the LC_(50) value, the first instar larvae were found to be very susceptible to A. muricata and the second instar larvae were found to be susceptible to A. graveolens, while the third and fourth instar larvae were found to be susceptible to M. siamensis. These extracts delayed larval development and inhibited adult emergence and had no adverse effects on P. reticulata at LC_(50) and LC_(90) values, except for the M. siamensis extract at its LC_(50) value.