Host range testing of Tamarixia dryi (Hymenoptera: Eulophidae) sourced from South Africa for classical biological control of Trioza erytreae (Hemiptera: Psyllidae) in Europe

Abstract

The African citrus psyllid, Trioza erytreae, vectors citrus greening or huanglongbing (HLB) disease. The psyllid has been reported from mainland Europe, where it is rapidly spreading from the northwest to the southwest of the Iberian Peninsula. In order to reduce its spread and population levels, a classical biological control program with the parasitoid Tamarixia dryi is under development in Spain. We evaluated the host specificity of T. dryi using 11 non-target psyllid (NTP) species, including five species of the genus Trioza. The psyllids were selected based on phylogenetic and ecological criteria. Tamarixia dryi exhibited a high host specificity. Females did not parasitize any of the 11 NTPs tested, except for one nymph of a gall-forming Trioza species closely related to Trioza montanetana. Tamarixia dryi only laid one egg on a nymph when it was removed from the gall on Convolvulus canariensis and exposed directly to the parasitoid. However, the immature parasitoid died before emerging. We further confirmed that T. dryi did not parasitize a representative triozid species, Trioza laurisilvae, of the endemic Canarian fauna after long time exposure. Our results demonstrate that T. dryi is a highly specific parasitoid and its introduction, release and establishment in Europe within the classical biological control program of T. erytreae should not affect other psyllid species. Therefore, no significant environmental impact is expected.