Abstract

A trial was conducted to assess the fumigant toxicity of the essential oils from Rosmarinus officinalis L., Salvia officinalis L., Lavandula angustifolia Mill. and Mentha balsamea Willd. against the adults of Sitophilus granarius(L.). The relationships between the time after treatment (1, 2, and 3 days), temperature (20, 25, 30, 35, and 40°C), concentration of essential oils (2.4 and 7.4 ml/L air) and mortality were investigated. In the experiment, the efficacy of the essential oils at 40°C was 95%, whereas their efficacy was considerably lower at lower temperatures (from 12 to 36%). Throughout the experiment, the essential oil of rosemary proved to be the most effective fumigant, causing more than 60% mortality of the granary weevil adults. When applying the essential oil of rosemary, more than 50% mortality in the adults of granary weevil was attained at 35°C (89%) and 40°C (99%). A satisfactory efficacy of the other essential oils, common lavender (90%), peppermint (97%) and common sage (94%), was attained only at the highest temperature. The activities of the essential oils were better at higher concentrations (36%) than at lower concentrations (32%). When assessing the effect of the concentration on the adult mortality, we achieved more than 50% efficacy only with rosemary (2.4 ml/L of air, 58%; 7.4 ml/L of air, 63%). The data for the other essential oils ranged between 19% (peppermint, 2.4 ml/L of air) and 34% (common sage, 7.4 ml/L of air). The calculated values for the LC₅₀ and LC₉₀ showed that only rosemary produced satisfactory fumigant activity on the adult granary weevils, especially in relation to the temperature. However, the positive efficacy identified in our laboratory experiments needs to be validated under conditions similar to those of the applied conditions, that is, warehouses.

Key words: Essential oils, granary weevil, stored-grain pest, fumigant toxicity.