Biology and host specificity of Spurgia capitigena (Bremi) (Dipt., Cecidomyiidae), for the biological control of Euphorbia esula L. in North America

Spurgia capitigena (Bremi) was evaluated as a potential biological control agent of leafy spurge, Euphorbia esula L. (species complex) in North Americ a. To ascertain the host specificity of this gall midge, tests were conduct ed in the field at Cavaillon, France, and at laboratories located in Rome, Italy and Bozeman, Montana, USA, in 1994 and 1995. Twenty-nine plant specie s, including eight native: North American euphorbias and biotypes of E. esu la, were evaluated. In the laboratory, the gall-midge was able to induce ga lls on seven species of spurges (all belonging to the subgenus Esula) and t he three accessions of leafy spurge. In field tests, S. capitigena infested only E. esula. The biology and host specificity of S. capitigena from Fran ce appears to be similar to that observed for Spurgia esulae Gagne from Ita ly (= Bayeria capitigena Bremi). In France, this gall-midge was commonly ob served from early May until October in habitats of very heavy and moist soi ls located along water channels, roadsides and in fruit orchards. Galls wer e induced on meristematic tissues, and thereby prevented flowering.