Relation between the composition of four essential oils from Algerian plants and theirinsecticidal activity against Sitophilus oryzae (L.) (Coleoptera: Curculionidae)and Tribolium confusum Jacquelin Du Val (Coleoptera: Tenebrionidae)

Abstract: Several essential oils (EOs) from Mediterranean plants are known to present asignificant biological activity on insect pests. The insecticidal activity of essential oils extractedby hydro-distillation from four aromatic plants from Algeria: spearmint (Mentha viridis), thyme(Thymus vulgaris), rosemary (Rosmarinus officinalis), and eucalyptus (Eucalyptus globulus), wastested either from contact test exposure (dose range: 0.05-0.4μl/cm2) or vapour phase exposure (single high dose: 0.582μl/cm3) against Sitophilus oryzae and Tribolium confusum. Therespective methodology of the two bioassays was the impregnated filter paper disk bioassay in aPetri dish and the closed chamber exposure. The chemical composition of the essential oils wasestablished by GC/MS analysis. Qualitative and quantitative analysis of the four EOs revealedthat their major chemical compounds were mainly monoterpenes. eucalyptus EO contained83.3% of three substances simultaneously eluted: limonene, 1,8-cineole and p-cymene; rosemaryEO contained 15.3% α-pinene and 14.2% camphor; thyme EO contained 43.2% thymol and34.4% carvacrol; spearmint contained 24.3% carvone, 8.3% 1,8-cineole and 8.1% limonene. Incontact toxicity test, the four EOs exhibited more or less a similar level of toxicity on both insectspecies. At the highest concentration (0.4μl/cm²), all the four EOs had similar average activityagainst S. oryzae with more than 88% mortality observed after 6 d exposure. For T. confusum,thyme, spearmint and rosemary EOs induced more than 95% mortality meanwhile eucalyptus EOcaused significantly less mortality observed at 72.6%. Among the four tested EOs, rosemary andmint EO showed the highest inhalation efficiency. The mortality rate reached 100% after 24hexposure time, either on S. oryzae or T. confusum. The analysis of the relationship betweeninsecticidal activity level on the two target insects and qualitative composition of the differentessential oils showed that the presence of oxygenated monoterpenes was linked to higherinsecticidal activity. To expect a future development of botanicals as a tool for integratedmanagement of pest in stored products new studies will be focused on identified pure bioactivecompounds.