Seasonal variations in chemical composition and fumigant activity of five Eucalyptus essential oils against three moth pests of stored dates in Tunisia

The present work investigates seasonal variation in chemical composition of essential oils isolated from leaves of five Eucalyptus species (Namely: Eucalyptus camaldulensis, Eucalyptus astringens, Eucalyptus leucoxylon, Eucalyptus lehmannii and Eucalyptus rudis) and assesses their fumigant activity against three stored-date moth pests: Ephestia kuehniella. Ephestia cautella and Ectomyelois ceratoniae. GC and GC-MS analyses showed that chemical composition varied with Eucalyptus species and seasons. The five essential oils contained 1,8-cineole, alpha-pinene, and alpha-terpineol as major common compounds. Of the other major constituents, beta-pinene and p-cymene were only present in E. rudis essential oil. In addition, o-cymene was specific only to E. camaldulensis and E. rudis essential oils. Oil yields were the highest and generally richer in toxic compounds during the summer season. Results demonstrated that fumigant toxicity varied with season, insect species, essential oil concentration and exposure time. E. camaldulensis essential oil was more toxic against E. cautella and E. kuehniella. LC50 values were respectively 11.07 and 26.73 mu l/l air while LT50 values were 13.49 and 30.46 h. However, for E. ceratoniae, E. rudis essential oil was more effective, with LC50 and LT50 values of 31.4 mu l/l air and 36.1 h respectively. For all pest species, fumigant activity was strongest for the summer season oils. E. cautella was the most sensitive species. (C) 2011 Elsevier Ltd. All rights reserved.