Larvicidal activity of extracts from Lippia kituiensis, Lippia javanica, Phytolacca dodecandra, Pittosphorum viridiflorum and Synadenium compactum against Rhipicephalus appendiculatus

Abstract

Rhipicephalus appendiculatus is a tick that transmit East Coast Fever to livestock. Use of synthetic acaricides for tick control, is limited by high costs, resistance, presence of chemical residues in animal products and environmental pollution. The use of plant-based products as a control strategy is regarded safe, and is widespread among pastoralists in Kenya and other parts of Africa. This study aimed at screening extracts of selected plants against Rhipicephalus appendiculatus larvae. These plants were Phytolacca dodecandra, Synadenium compactum, Pittosphorum viridiflorum, Lippia kituiensis and Lippia javanica. Methanol extraction were done on the selected plants and the resultant methanol crude extracts subjected to preliminary bioassay screening against R. appendiculatus larvae using contact toxicity. Sequential extractions were done on bioactive methanol extracts using water, hexane and ethyl acetate. The resultant extracts were subjected to bioassay against the larvae. From the start of the experiment, mortality data was obtained at 6, 12, 24 and 48 hrs. LC50 and LC90 in mg/ml were determined for each extract using SPSS. Methanol extracts of L. kituiensis, P. viridiflorum, and P. dodecandra had LC50 of 21.3 (18.1-24.5), 30.5 (25.7- 35.1) and 39.1 (31.1-46.9) while LC90 were 38.6 (32.5-51.6), 63.1 (52.7-83.9), 84.6 (67.7-124.2) at 48 hrs respectively. Hexane extract of L. kituiensis had LC50 of 12.6 (11.0-14.1), 10.6 (9.0-12.0), 6.7 (5.2-7.9), and 4.8 (2.2-5.9) and LC90 of 19.5 (17.0-24.4), 17.4 (15.0-22.0), 10.8 (9.1-14.3) and 7.7 (6.3-13.0) at 6, 12, 24 and 48 hrs respectively. At 48 hrs, hexane extract of P. viridiflorum had LC50 of 22.5 (18.3-26.6) and LC90 of 45.5 (36.9-66.8) while aqueous extract of P. dodecandra had LC50 of 17.3 (15.2-19.4) and LC90 of 26.8 (23.3-34.4). Hydro-distillation of fresh leaves of L. kituiensis and L. javanica resulted in essential oil production, which was also subjected to the larvae and LC50 and LC90 in mg/ml determined. The LC50 were 3.3 (3.1-3.3), 3.2 (3.1-3.3), 3.1 (3.0-3.2) and 3.1 (3.0-3.2) for L. kituiensis oil and 3.1 (3.0-3.2), 3.1 (3.0-3.2), 3.0 (2.9-3.1), 2.9 (2.8-3.1) for L. javanica oil at 6, 12, 24 and 48 hrs respectively. LC90 were 4.1 (3.9-4.4), 4.0 (3.8-4.3), 3.9 (3.8-4.2), 3.9(3.7-4.1) for L. kituiensis oil and 3.9 (3.7-4.2), 3.9 (3.7-4.2), 3.8 (3.6-4.1), 3.7 (3.6-4.0) for L. javanica at 6, 12, 24 and 48 hrs respectively. Cytotoxicity analysis using vero cells were done on extracts that showed bioactivity against the larvae and none of the extracts was cytotoxic hence were considered safe for practical use. Due to potency observed in the selected plants against the larvae, they could be used as lead compounds for the development of plant based acaricides.