Chemical composition and bioactivity of essential oil from Eucalyptus occidentalis leaves against two stored product pests

Attempts have been made in recent years to reduce the use of synthetic pesticides and seek alternative and innovative methods for pest control. We conducted a study on the chemical composition ofEucalyptus occidentalisessential oil and investigated the fumigant, contact and repellent effects againstTribolium castaneum(Herbst) (Col: Tenebrionidae) andRhyzopertha dominica(F.) (Col: Bostrichidae). The major components were τ-cadinol (17.20), 1,8-cineol (15.5%), α-cadinol (14%) and α-pinene (9.21%). The contact toxicity experiment showed that the oil was more toxic toR. dominica(LD50value 0.82 μL/cm) than toT. castaneum(LD50value 0.99 μL/cm) and showed the same fumigant toxicity for both insects according to the 95% confidence limit of LC50. The repellency againstT. castaneumwas more than forR. dominicaand increased from 14 to 75% forR. dominicaand 22 to 78% forT. castaneumafter 2 h. These results suggest thatE. occidentalisessential oil is a potential candidate for use as a natural repellent and insecticide for stored-product insect pests.

Effect of genetic relatedness among parents on gain in salt tolerance in progeny of crosses of Eucalyptus occidentalis

Genetic diversity of a Eucalyptus occidentalis breeding population screened for salt and waterlogging tolerance was examined using eight microsatellite loci. Mating using an immature style ‘one stop pollination’ method between parents was carried out to produce progeny for testing under 500 mM salt waterlogging. The effect of parental genetic distance on seed production and early seedling survival was examined and inheritance of salt/or waterlogging tolerance was assessed by testing performance of progeny in comparison to parents. Diversity was moderate among the nine provenances and the families, and most of the diversity was distributed within rather than between families. Genetic relationships showed no structure in relation to provenance indicating any adaptation to saline environments has not affected genetic similarity. Breeding for salt and water tolerance may be achieved without decline in genetic diversity. There was a significant correlation between capsule production and parental genetic distance and a positive trend between increasing parental genetic distance and increasing number of germinated seeds/capsule, and seedling survival at 2 weeks and 9 months. These trends indicate expression of inbreeding depression in crosses between genetically similar parents. Heritability values, under 500 mM salt-waterlogging treatment, indicated that height had moderate heritability (h2 = 0.5). Crosses with the widest parental genetic distance produced progeny with considerable height increase above parents and this trend was evident even with moderate genetic distance indicating crossing at this level of differentiation may achieve optimum breeding gain.