The Search for Effective Biological Control Agents in Europe: History and Lessons from Leafy Spurge (Euphorbia esula L.) and Cypress Spurge (Euphorbia cyparissias L.)

During field surveys made in Europe nearly 40 specialized insect species were found and considered as potential biological control agents of leafy spurge and cypress spurge ( Euphorbia esula and Euphorbia cyparissias ). More insect species were found on the most common and the geographically most widespread spurge species and on those occurring in a wide range of habitat types. The insect families most frequently associated with perennial spurges in Europe are the chrysomelids, sesiids, cecidomyids, and anthomyiids. Although the areas surveyed include only the most western parts of the leafy spurge and cypress spurge distribution in the Palearctic, all food niches and habitats of the target weeds were found to be occupied by herbivorous insects. The history of the search for biological control agents of leafy and cypress spurges in Europe is briefly reviewed. The selection of candidate agents during the past 30 years is discussed, and the 22 insect species which have been screened so far are briefly considered. It is concluded that suitable agents were found outside optimal survey areas with regard to ecoclimatic and host-plant matching.