Fatty acid composition and biological activity of four olive oils from Kabylia (Algeria) against Rhyzopertha dominica (Coleoptera: Bostrychidae) infesting wheat seeds

Abstract

The use of conventional insecticides is one of the most widely used methods of controlling pests of stored grains. But the presence of toxic residues in treated commodities and the emergence of insect resistant strains are becoming a growing concern. Olive oil is well known throughout the world for its benefits to human health, but little known for its biological activity against insect pests.The aim of this work is to study the fatty acid composition and the insecticidal activity of oils according to origin of plantation, against one of the main insect pests of stored grain Rhyzopertha dominica (Coleoptera: Bostrychidae). The olive oils were obtained using an oleodoser from olives of the 'Chemlal' variety harvested in 4 olive groves in Kabylia (Algeria) and the analysis of the fatty acid composition was carried out by gas chromatography. The main fatty acids found are oleic, palmitic and linoleic acids. Biological tests conducted under laboratory conditions, at a temperature of 30±1°C and a relative humidity of 70 ± 5 %, revealed that the 4 olive oils, applied on soft wheat grains, showed a contact toxicity against R. dominica. The toxicity of the oils varied as a function of the dose and the duration of treatments. After 24 h of exposure, all oils tested at the highest dose (0.4 mL/25 g) were found to be highly toxic to adults of R. dominica, with mortality rates ranging from 72.5 to 95 %. The toxicity of the 4 oils based on the LD50 (mL/25 g) values for 24 h mortality is established as follows: Maatkas (213), Bachloul (232), Tadmait (234) and M'Chedellah (263). The number of the F1 offspring decreases as the dose of oil is increased to reach zero with the highest dose, for all treatments. All oils tested completely preserve soft wheat seeds from R. dominica attacks using the same highest dose. On the other hand, results also revealed that treatments with olive oil do not affect the germination capacity of soft wheat seeds.