Repellency and toxicity of essential oils from the leaves and bark of Laurelia sempervirens and Drimys winteri against Tribolium castaneum

We report here on the repellent activity, as well as contact and fumigant toxicity, of four essential oils extracted from the leaves and bark of Laurelia sempervirens and Drimys winteri against an important stored-product insect pest: the red flour beetle, Tribolium castaneum. The four oils tested had a very strong repellent activity towards T. castaneum when tested in a filter paper arena test. After 4 h exposure >90% repellency was achieved with L. sempervirens oils at low concentrations of 0.032 μl/cm2, while for D. winteri oils concentrations of 3–10 times higher were needed to achieve this activity. Oils of both, L. sempervirens and D. winteri, were found to be toxic towards T. castaneum when applied topically or by fumigation. LD50 values by topical application of L. sempervirens oils were from 39 to 44 μg/mg insect; for D. winteri oils these were from 75 to 85 μg/mg insect. By fumigation, LC50 values for L. sempervirens oils were 1.6–1.7 μl/l air, while these were 9.0–10.5 μl/l air for D. winteri oils. In addition, with L. sempervirens oils 50% of the tested beetles were killed at 100 <μl/l air within 3.0–4.4 h, while with D. winteri oils the LT50 values were 6.1–7.4 h. The results obtained are discussed in relation to the main constituents of the oil extracts. In conclusion, the essential oils from the leaves and bark of L. sempervirens may be explored as a potential natural insecticide for stored-product insect pests because of their high repellency and insecticidal activities.