Effects of spurge flax (Daphne gnidium L., Thymelaeaceae) extracts on the development and mortality of the elm leaf beetle (Coleoptera: Chrysomelidae)

Spurge flax (Daphne gnidium L., Thymelaeaceae) is an evergreen shrub typical of the Mediterranean flora. It has been traditionally used for centuries in Spain as a control agent of invertebrate pests of crops and cattle. Previuos bioassays performed in our laboratory demonstrated that leaves and ethanolic extracts of D. gnidium showed antifeedant activity on pest species belonging to the orders Heteroptera, Isoptera, Lepidoptera and Coleoptera. The elm leaf beetle, Galerucella luteola Müller (Coleoptera, Chrysomelidae), in Spain represents one of the most important pests of elms (Ulmus spp.) in both river bank forests and urban areas, being responsible for partial or total defoliation of the tree tops. In order to study the effects of spurge flax on G. luteola, different doses of an ethanolic extract of D. gnidium were added to the natural diet (elm leaves) of young larvae. During the development, weight changes, phase durations and mortality rates of each stage were recorded. Results showed that the addition of spurge flax extract to the diet of G. luteola induced: a) a significant increase in the duration of the larval period; b) greater mortality rates for all stages; c) weight reduction of individuals of all stages, including imagoes.