Efficacy of Essential Oils from Ocimum kenyense as a Biopesticide against Aphis gosypii, Thrips tabaci and Bemisia tabaci.

Abstract

Natural sources of biopesticides such as plants and microorganisms are widely employed for pest management globally. Over the last five decades, the use of biopesticides has been explored as a safer alternative to synthetic pesticides. This study determined the repellence and contact toxicity of essential oils from Ocimum kenyense plant against Thrips tabaci, Bemisia tabaci, and Aphis gosypii. The essential oils (Eos) were extracted from dry leaves by hydrodistillation using the Clevenger apparatus for 8 hours. The composition of essential oils was qualitatively and quantitatively analysed using GC-MS, while ATR-FTIR was used to determine the functional groups. The major compound ion in the Eos was 1,8-Cionele while the major phytochemical identified was Eucalyptol Bioassay of the crude extracts were carried out on T. tabaci, B. tabaci, and A. gosypii. Contact toxicity and repellency tests against mixed-sex adult pests were carried out on T. tabaci, B. tabaci, and A. gosypii. In contact toxicity, five different concentrations were prepared and each was replicated five times. Acetone was used as a negative control, while permethrin, a commercial chemical pesticide was used as a positive control. The LD50 of the essential oils was determined by Probit analysis SPSS version 26.0. The response to the treatments was observed after 24 hours by using a blunt object probing and the pests that did not respond were counted as dead. It was found that essential oils from O. kenyense had the lowest LD50 of 0.127 µL against A. gosypii. This implies that O. kenyense can be used as a contact toxicant against A. gosypii. Repellency tests were carried out at four different concentrations. N, N-Diethyltoluamide (DEET) repellent from a commercial mosquito repellent was used to compare the effectiveness of the essential oils against commercial repellents. The repellency test responses were observed after 1 hour and the data was used to determine the correlation between different levels of concentration of Eos and percentage repellency of Eos of O. kenyense leaves carried out at α=0.05. There was a high correlation of 1.000 between the increase in concentration of Eos and repellency against A. gosypii, T. tabaci and B. tabaci. The results were statistically significant and (P<0.05, α=0.05). Therefore, essential oils from O. kenyense can be used as a contact toxicant biopesticide against A. gosypii and a repellent biopesticide against A. gosypii, T. tabaci and B. tabaci.