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Title: Genetic and morphological studies of Trichosirocalus species introduced to North America, Australia and New Zealand for the biological control of thistles

item DE BIASE, ALESSIO - University Of Rome Sapienza
item COLONELLI, ENZO - Retired Non ARS Employee
item BELVEDERE, SILVIA - University Of Rome Sapienza
item LA MARCA, ALESSANDRA - Bbca-Onlus, Italy
item CRISTOFARO, MASSIMO - Enea Casaccia Research Center
item Smith, Lincoln

Submitted to: Bulletin of Entomological Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/9/2015
Publication Date: 2/1/2016
Citation: De Biase, A., Colonelli, E., Belvedere, S., La Marca, A., Cristofaro, M., Smith, L. 2016. Genetic and morphological studies of Trichosirocalus species introduced to North America, Australia and New Zealand for the biological control of thistles. Bulletin of Entomological Research. 106(1): 99-113. doi:10.1017/S000748531500084X.

Interpretive Summary: Taxonomic identification of biological control agents of invasive alien weeds is critical for correctly documenting information on host plant specificity and potential efficacy. It is crucial for developing new biological control agents that do not harm nontarget plants. Modern methods of molecular genetics have significantly improved our ability to distinguish species and subspecific populations that differ in their host plant specificity. The weevil, Trichosirocalus horridus, has been used in North America, Australia and New Zealand to control several invasive thistle species (Carduus, Cirsium, Onopordum), starting in 1974. However, in 2002 morphologically-based taxonomic studies divided this "species" into three species, which were purported to each prefer different host plants. Subsequent field studies showed inconsistencies in this new taxonomy, so we conducted a molecular genetic analysis to correlate host plant, insect morphology and genetics. Our results show that one of the species does not exist (T. mortadelo), that T. horridus is genetically diverse and has a wide host range, and that T. briesei is specific to one genus (Onopordum). All specimens analyzed from North America belong to T. horridus, which helps explain why this insect has been reported to attack nontarget Cirsium species.

Technical Abstract: Trichosirocalus horridus sensu lato has been used as a classical biological control agent of several invasive alien thistles (Carduus spp., Cirsium spp. and Onopordum spp.) since 1974. Trichosirocalus horridus was recognized as a single species until 2002, when it was split into three species based on morphological characters: T. horridus, T. briesei and T. mortadelo, each purported to have different host plants. Because of this taxonomic change, we are not certain which species were released in various countries, furthermore, there appear to be some exceptions to the purported host plants of some of these species. To resolve these questions, we conducted an integrative taxonomic study of the T. horridus species complex using molecular genetic and morphological analyses on specimens from three continents. Both mitochondrial (cox1) and nuclear (ef1a) markers clearly indicate that there are only two distinct species: T. horridus and T. briesei. Molecular evidence, morphological analysis and host plant associations support the synonymy of Trichosirocalus horridus (Panzer, 1801) and T. mortadelo Alonso-Zarazaga and Sánchez-Ruiz, 2002. We determined that T. horridus has been established in Canada, USA, New Zealand and Australia, and that T. briesei is established in Australia. The former species was collected from Carduus, Cirsium and Onopordum spp. in the field, whereas the latter appears to be specific to Onopordum.