Evaluation of the chemical composition and bioactivity of essential oils from Cinnamomum camphora (L.) J.Presl. (Lauraceae), Piper nigrum L. (Piperaceae) and Stemona japonica (Miq.) (Stemonaceae) against Oryzaephilus surinamensis (Linnaeus, 1758) (Coleoptera: Silvanidae)

Oryzaephilus surinamensis is a serious insect pest of many stored products. Repellency and fumigation tests were performed to manage it. Essential oils (EO) from three plants – Cinnamomum camphora, Piper nigrum and Stemona japonica – were tested on Oryzaephilus surinamensis in the laboratory. Repellency was tested on filter paper in Petri dishes at a concentration of 31.4 μg/cm2, and 20 adults (10 days old) were observed for repellency behaviour 12, 24, 48 and 96 hours after the bioassay without any food. Cinnamomum camphora EO was the strongest repellent (83.75 ± 1.83%), followed by the Piper nigrum and Stemona japonica EOs. The eggs were obtained by maintaining 20 individuals (males and females) for 24 h in a 100 mL glass jar containing 5 g of diet feed. To evaluate the effect of EO on the development of larvae and adults, a filter paper disc impregnated with 0.1 mL of EO was placed on the inner side of the lid of the jar containing the eggs and diet feed. After 40 days, the number of adults and larvae in the jar was counted. All three EOs exhibited bioactivity against the development of larvae and adults. A relatively low number of larvae and adults was recorded in Cinnamomum camphora, followed by Stemona japonica and Piper nigrum. Gas chromatography/mass spectrometry was used to identify the major compounds in the EOs. Further studies are recommended to evaluate their bioactivity against different insect pests in stored seeds