Growth inhibitory activity of Daphne gnidium L. (Thymelaeaceae) extracts on the elm leaf beetle (Coleoptera, Chrysomelidae)

An investigation has been performed on the activity of spurge flax (Daphne gnidium L., Thymelaeaceae), a typical component of the Mediterranean vegetation, on the development of the elm leaf beetle (Xanthogaleruca luteola Muller; Col., Chrysomelidae), one of the most serious defoliators of urban forests. Different concentrations of ethanolic extracts of D. gnidium leaves were added to the natural diet (elm leaf discs) of X. luteola, starting with L2 larvae, and the effects induced on the vitality, growth and phase duration of the different stages have been evaluated. A significant reduction of larval survival and adult emergence, together with an increased length of the larval period, heavy reduction of weight gain and appearance of malformations in emerged imagines were observed in presence of spurge flax extracts. These findings agree to ascribe to D. gnidium leaf extracts a growth inhibitory activity and allowed identifying what should be the optimal concentration to be applied on elm leaves to prevent heavy damages by X. luteola.