Repellent Effects of Five Monoterpenoid Odours Against Two Stored Product Insect Pests

Five monoterpenoids, (R)-linalool. 1,8-cineole. (S)-2-heptyl acetate, (S)-2-heptanol, and citral, which are natural components of the essential oils of Afratnomum melegueta (K. Schum) and Zingiber officinale (Roscoe), were tested at the ratios in which they occur naturally against Tribolium castaneutn (Herbst.), and Rhyzopertha dominica (Fab.) in a 4-way olfactometer. The results showed the repellent properties of the compounds as both beetles spent less time in the olfactometer arm containing the test stimuli. Linalool and (S)-2-heptanol were stronger repellent compounds than the others. With linalool, T. castaneum significantly preferred the control arms (spending 2.78 ± 0.22 min in them) compared to the test arms (1.22 ± 0.22 rnin.). For R. dominica the times spent were 2.87 ± 0.26 min in the control anTISand 0.89 ± 0.28 min in the test arm. With (S)-2-heptanol, T. castaneum spent 1.23 ± 0.27 min in the test arm compared to 2.83 ± 0.23 min in the control arms. R. dominica spent 1.61 ± 0.24 min in the test arm and 2.69 ± 0.23 min in the control arms. For the number of entries or visits made. R. dominica made significantly fewer visits to linalool-treated arm (P= 0.018) and (S)-2-heptanol treated arm (P=0.038) compared to the control arms. These compounds could be suitable as repellents or fumigants against stored product pests in a small-scale farmer level.