Fly in the ointment: Host specificity challenges for Botanophila turcica, a candidate agent for the biological control of saffron thistle in Australia

Authors: LESIEUR, VINCENT - Csiro European Laboratory; THOMANN, THIERRY - Csiro European Laboratory; JOURDAN, MIREILLE - Csiro European Laboratory; KASHEFI, JAVID - European Biological Control Laboratory (EBCL); BON, MARIE-CLAUDE - European Biological Control Laboratory (EBCL)

Submitted to: Insects
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/24/2025
Publication Date: 3/28/2025
Citation: Lesieur, V., Thomann, T., Jourdan, M., Kashefi, J., Bon, M. 2025. Fly in the ointment: Host specificity challenges for Botanophila turcica, a candidate agent for the biological control of saffron thistle in Australia. Insects. 16(4): 357. https://doi.org/10.3390/insects16040357.
DOI: https://doi.org/10.3390/insects16040357

Interpretive Summary: The saffron thistle, Carthamus lanatus, is a USDA federally listed noxious weed and can be considered one of the worst pasture weeds in North America including California, Oregon and in Australia. It is heavily protected with sharp spines and produces an abundance of moderately long-lived seeds. In dense infestations, it imposes significant impediments to the forage production and quality while also creating physical barriers to grazing access. A crown feeding fly, Botanophila turcica, has been targeted by Australia as a potential biocontrol agent due to previous studies that have shown its specificity to the weed. However, recent studies conducted in Greece reported that this candidate agent may also infest a closely related crop to the saffron thistle, namely safflower. To verify the lack of specificity, host specificity testing in the field supported by analysis of the DNA of the flies were conducted in France. Findings revealed that B. turcica can develop on saffron thistle, safflower, and other related plants. This means that while B. turcica could help control saffron thistle, it also could poses a risk to safflower crops. Further research is needed to understand the conditions under which B. turcica attacks safflower in order to assess the potential risk to safflower growers in Australia and USA.

Technical Abstract: In this study, we investigated if the rosette crown-feeding fly Botanophila turcica Hennig (Diptera: Anthomyiidae) could be considered a potential candidate to control saffron thistle, Carthamus lanatus L. (Asteraceae: Cardueae) in Australia. Previous studies indicated that B. turcica is host specific to Ca. lanatus and did not infest the closely related crop, safflower (Carthamus tinctorius L.). However, more recent field observations made in Greece reported that B. turcica infested safflower in cultivated fields. To determine if B. turcica is safe for release as a biocontrol agent, we re-examined the host range of B. turcica by performing new host-specificity testing combined with field surveys carried out in the south of France during two consecutive years. We also investigated the species identity of the flies by comparing DNA sequences (COI barcode region) of specimens collected in France from Ca. lanatus and Centaurea solstitialis L. with those from Greece collected from Ce. solstitialis and Ce. diffusa Lam. Our COI analyses confirmed that French and Greek samples identified as B. turcica belonged to the same species, while a second group of Greek samples matched B. brunneilinea, indicating two distinct species. Our results also demonstrated that B. turcica has a wider host range than previously suggested. Laboratory testing indicated that Ca. lanatus, Ca. tinctorius, and Ce. solstitialis are suitable hosts for the development of B. turcica. Field surveys also revealed that Ce. diffusa is part of the host range of the fly. Based on the results reported here, B. turcica may have the potential to control both the target weed, Ca. lanatus, and Ce. Solstitialis, but it may also be a serious threat to safflower production. Further investigations to assess under what conditions B. turcica attacks Ca. tinctorius may help clarify the level of risk to Australian and potentially to American growers.