Phytochemical composition and in-vitro acaricidal activity of crude fruit extracts of solanum incanum against rhiphicephalus appendiculatus from cattle

Abstract

Ticks, particularly R. appendiculatus which pose significant challenges to cattle production in Uganda are mainly managed using conventional acaricides but these have limitations among which is tick resistance which forces farmers to opt for medicinal plant alternatives such as Solanum incanum (S. incanum). However, studies which validate the acaricidal activity of S. incanum in Uganda hardly exist. The major aim of this study was to determine the qualitative phytochemical composition and in-vitro acaricide activity of aqueous and 95% ethanolic extracts of S. incanum fruit against R. appendiculatus ticks. Solanum incanum is a hardy perennial shrub native to Africa known for its medicinal and pesticide properties. Plant samples (S. incanum fruit) were collected from Mpigi district Uganda, dried and processed to obtain aqueous and 95% ethanolic extracts. The methods used were cold maceration for ethanolic extraction and decoction for aqueous extraction. Standard methods were use to determine qualitative phytochemical composition. Ticks were collected from naturally infested cattle in Mpigi district, Uganda, identified morphologically and larvae were reared under controlled laboratory environment. The in-vitro larval immersion test was conducted at various concentrations (6.25,12.5,25,50,100mg/ml) and time to kill 100% tick larvae for both extracts observed for. Data were analyzed with Excel and SPSS to calculate effective concentration (EC₅₀) values and compute time to kill mean±SD, respectively. The aqueous extracts (9.8%) of S. incanum fruit had a higher percentage extraction yield compared to the ethanolic extract (8.2%). Saponins were highly concentrated in aqueous extracts and appeared as traces in ethanolic extracts. Tannins, alkaloids, flavonoids, courmarins and steroid glycosides appeared as traces in both extracts. The time to kill 100% tick larvae which was taken by the positive control Amitraz (24± 0.0 hours) was comparable to that of 100 mg/ml aqueous extract of S. incanum fruit, whereas the 95% ethanolic extract (100mg/ml) took more time (48± 1.2 hours). There was no significant difference between the 100mg/ml S. incanum aqueous (P=0.800) and the positive control (Amitraz). Effective concentration (EC₅₀) values were lower for aqueous extract (44.15 mg/mL) of S. incanum fruit compared to the 95% ethanolic extract (280.18 mg/mL). Given the shorter time to kill tick larvae which was comparable to the positive control Amitraz and the low EC50 exhibited by the aqueous S. incanum fruit extracts. This validates farmers claims and practices since farmers usually use water to make ethnoveterinary preparations. This calls for further studies using actual animals to validate and standardize the aqueous S. incanum fruit extract preparations.