The biology and host specificity ofOxicesta geographicaF. from Romania, Hungary, and Southwestern Russia were studied to evaluate the potential of this moth as a new biological control agent of leafy spurge,Euphorbia esulaL., “complex” in North America. This oligophagous, multivoltine tent caterpillar is common on perennial spurges in southeastern Europe and Asia Minor and prefers dry, open sites. Results of no-choice feeding tests with first instars on 93 plant species and biotypes, distributed in 33 families, show thatO. geographicacompleted its life cycle mainly on plants ofEuphorbia, subgenusEsula, and occasionally fed and developed on species in other subgenera of the genus. Studies of late instars did not show any important extensions of the host range.