DNA barcoding of endophagous immature stages elucidates the host-plant affinities of insects associated with the invasive Senecio madagascariensis in its native range in South Africa

Senecio madagascariensis Poiret (Asteraceae), an invasive herb from southern Africa that inflicts high economic losses in several countries worldwide, is currently a target for biological control in Australia and Hawaii. Several candidate insect agents were identified from the weed's native range in South Africa. Confirmation of narrow host ranges, prior to agent importations into quarantine, is important for Australia given its rich native Senecio flora. In particular, surveys for candidate agents on closely related non-target plants in the native range can differentiate between host specific and unsuitable agents at an early stage. This study focused on endophagous insects from families that were deployed in biocontrol programmes against other weedy Asteraceae. The hostplant affinities of stem-boring Coleoptera and stem-boring and capitulum-feeding Lepidoptera and Diptera were assessed across 18 native herbaceous Senecio species in KwaZulu-Natal, South Africa. Since larval morphology is typically unable to confirm insect identity, DNA barcoding was used to differentiate between insect species associated with different Senecio species to determine their host-plant affinities. COI phylogenies revealed that stem-boring Curculionidae and Tortricidae and capitulum-feeding Pterophoridae and Tephritidae that are associated with S. madagascariensis were restricted to plants in the S. madagascariensis species complex. In contrast, none of the stem-boring Agromyzidae were restricted to S. madagascariensis or its species complex. This study has supported the selection of several potentially host-specific agents for S. madagascariensis that could be imported for quarantine testing in Australia and Hawaii.