Insecticidal activities of volatile oils of lime fruit peels and African black pepper seeds on adult kola weevil and their chemical compositions

Balanogastris kolae reduces the quality of stored kolanuts; yet, plants with insecticidal properties could be used to manage this insect pest. The objective of this study was to evaluate the efficacy of plant oils against B. kolae, a storage pest of kolanuts. The Citrus aurantifolia fruit peel and Piper guineense seed volatile oils obtained via hydro-distillation of the dried, pulverised samples were tested. Their chemical composition was determined using Gas Chromatography-Mass Spectrometry (GC-MS) analysis. Adult mortality was generally low (0.0%) across treatments and exposure times, though not significant (P > 0.05) in the fumigant tests The highest mortality (47.5%) was recorded at 24 hours in 1.0% P. guineense, while the mortality was 13.1% occurred at 12 hours in the 15.0% C. aurantifolia concentration. In contact toxicity tests, none of the weevils treated with 10.0% C. aurantifolia survived after 24 hours of exposure. The highest mortality (85.0%) was obtained from the 10.0 and 15.0% P. guineense volatile oil after 96 hours. Citrus aurantifolia elicited contact toxicity against the weevil more than P. guineense across all concentrations. The GC-MS analysis gave 33 compounds in C. aurantifolia and 43 in P. guineense volatile oil samples. The prominent compounds were limonene (3.222%), linalyl isobutyrate (2.484%), gamma-caryophyllene (1.197%) and Patchoulene (6.529%). Therefore, C. aurantifolia fruit peel and P. guineense seed volatile oils are efficacios in controlling Balanogastris kolae insect pest infestation on kolanuts, though C. aurantifolia fruit peel oil is the best as it compares closely with the synthetic pesticide (2,2-dimethyl dichlorovinyl phosphate (DDVP)).