Evaluation of acaricidal activity of methanolic and aqueous extracts of Ricinus communis against Rhipicephalus decoloratus ticks

Abstract

Ticks and tick-borne diseases in cattle keeping communities is one of the leading economic constraints to productivity. Significant losses are incurred by farmers through control of ticks and treatment of tick-borne diseases (TBDs). The 2019 report of the presidential Technical advisory committee on TTBDs showed that Uganda loses over 1.1 billion USD due to this TTBDs menace. Farmers mainly rely on the use of acaricides for tick control, however, due to failure of some of the acaricides on the market as evidenced by numerous research works in the country, it is prudent that supportive alternatives of TTBDs control are explored. In this study, the in-vitro Adult Immersion Test (AIT) assays to evaluate the acaricidal activity of Ricinus communis leaf extracts on Rhipicephalus decoloratus ticks were conducted. Both the plant and tick samples were collected from Kyegegwa district. Aqueous and methanolic extracts of Ricinus communis were prepared using cold maceration method. The collected ticks were sorted to only select viable engorged ticks for the AIT assay. AIT assays were conducted for the aqueous and methanolic extracts at concentrations of 2.5%, 5%, and 10%. Two commercially available acaricides (Organophosphate (OP) and an Amitraz) were included alongside the assays for comparative purposes. Observation for tick mortality was done at intervals of 36hrs, 72hrs, 7days and 14days. At 36hrs the methanolic extract had caused 0%, 8.3%, 16.7% tick mortalities in the 2.5%, 5%, 10% concentrations respectively while the aqueous extract had caused no tick mortalities at all concentrations. At 7days, the methanolic extract had caused 8.3%, 33.3%, 41.7% tick mortalities in the 2.5%, 5%, 10% concentrations respectively while the aqueous extract had only caused 8.3% mortality in 10% concentration. No mortalities were recorded in the OP and Amitraz at 36hrs and 7days. The oviposition inhibition (OI) at day7 was highest in the 10% methanolic extract showing 58.3%. The Amitraz and organophosphate caused 0% and 100% oviposition inhibition respectively. These results thus show that the methanolic extract of Ricinus communis can be used as an alternative tick control measure if subjected to further investigation. The lack of mortality in the Amitraz and organophosphate groups could mean a possible resistance by the tested tick population to these two compounds.