Host-plant affinities of stem-boring weevils and moths associated with fireweed (Senecio madagascariensis) in South Africa: evaluating native host ranges of candidate biocontrol agents using DNA barcoding

ABSTRACT

Native to South Africa and Madagascar, the invasive fireweed, Senecio madagascariensis Poiret (Asteraceae), is a target for biological control in Australia and Hawaii, where substantial infestations persist. Earlier studies in the weed’s region of origin, namely KwaZulu-Natal Province in South Africa, assessed the seasonal abundance of stem-boring insect herbivores in S. madagascariensis populations. The weevil Gasteroclisus tricostalis (Thunberg) (Curculionidae) and moth Metamesia elegans (Walsingham) (Tortricidae) were prioritised as candidate agents for Australia due to their persistence across seasons. In this study, the host ranges of these two candidate agents were assessed by comparing the stem-boring curculionids and lepidopterans that are associated with S. madagascariensis with those associated with non-target Senecio species in the KwaZulu-Natal Midlands region. DNA barcoding of the adults and endophagous larvae recovered during field sampling of S. madagascariensis and 17 non-target Senecio species in 2017/18, as well as those from earlier field surveys, was used to differentiate the insect species and elucidate their host-plant affinities. Although weevil larvae were recovered from the stems of seven non-target Senecio species, G. tricostalis was associated only with Senecio inaequidens DC. and Senecio skirrhodon DC., both in the S. madagascariensis species complex. Lepidopteran larvae were associated with three non-target Senecio species, all in the S. madagascariensis species complex, with M. elegans associated only with Senecio harveianus MacOwan and S. inaequidens. These results suggest that G. tricostalis and M. elegans have restricted host ranges and that further host-specificity studies in quarantine are warranted to demonstrate their suitability for release.

KEYWORDS:

• Agent host range
• cytochrome oxidase I gene sequencing
• stem borers
• weed biocontrol

Acknowledgements

This study was funded by the Australia Government Department of Agriculture, Fisheries and Forestry (formerly Department of Agriculture, Water and the Environment), building on work undertaken through the Agricultural Competitiveness White paper – Established Pest Animals and Weeds Measure. Support from the Bega Valley Fireweed Association, notably N. Watson, is acknowledged. Financial support for the first author was provided by the National Research Foundation of South Africa and the University of KwaZulu-Natal (UKZN). We are grateful to O. Zuma and S. Hakizimana (UKZN) for assisting with field collections and A. Govender (UKZN) for assisting with the genetic aspects of the study. The context for the study was facilitated by discussions with A.W. Sheppard (Commonwealth Scientific and Industrial Research Organisation (CSIRO), Canberra, Australia) and K.J. Harvey (New South Wales Department of Primary Industries – Biosecurity and Food Safety, Orange, Australia). P. Jones (CSIRO, Canberra) provided comments on an earlier draft of the manuscript. The comments of four anonymous reviewers improved the manuscript.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by University of KwaZulu-Natal; Australia Government Department of Agriculture, Fisheries and Forestry; National Research Foundation of South Africa.