Which species of the thistle biocontrol agent Trichosirocalus are present in New Zealand?

摘要

Trichosirocalus horridus (Panzer) (Coleoptera: Curculionidae), nodding thistle crown weevil, was introduced to New Zealand in 1989 for classical biological control of Carduus nutans L. (nodding thistle). Later, it was introduced from New Zealand to Australia. In 2002, a revision of the species concluded that T. horridus was in fact a complex of three species, with distinct host plant genus preferences: T. horridus, Trichosirocalus mortadelo Alonso-Zarazaga and Sanchez-Ruiz, and Trichosirocalus briesei Alonso-Zarazaga and Sanchez-Ruiz with preferences for Cirsium, Carduus and Onopordum thistles, respectively. In the revision, crown weevils on Carduus thistles in Australia were identified as all T. mortadelo, sourced from New Zealand. This suggests that the original introductions into New Zealand were wholly or partly T. mortadelo. A survey conducted to confirm which species of Trichosirocalus are present in New Zealand shows that all adults collected here are T. horridus regardless of whether the source host was Cirsium vulgare (Savi) Tenore or C. nutans. This presents two paradoxes: firstly, that T. mortadelo was collected from New Zealand and shipped to Australia but has not been found in our surveys, and secondly, that T. horridus does not showdistinct preference for Cirsium thistles in New Zealand as reported elsewhere.