Author
Graeme W Bourdȏt
graeme.bourdot@gmail.com
Bioeconomy Science Institute
Lincoln
Coauthors
Shona Lamoureaux, Bioeconomy Science Institute, Lincoln, New Zealand
Michael Cripps, Lincoln University, Lincoln, New Zealand
Darren Kriticos, Cervantes Agritech Pty Ltd, ACT, Australia
Alasdair Noble, Bioeconomy Science Institute, Lincoln, New Zealand
Jessica Kriticos, Cervantes Agritech Pty Ltd, ACT, Australia
Abstract
The leaf-feeding beetle, Cassida rubiginosa, was introduced into New Zealand from Europe in 2007 as a biological control agent for Cirsium arvense (Californian thistle) and is now widely distributed. To explore the extent to which geographically variable climate might explain spatial variation in the beetle’s observed impact, we developed a climate-niche model for each of the species using CLIMEX. The models reveal that the climate throughout most of New Zealand is variably suitable for both species, although everywhere relatively less suitable for the beetle (Bourdôt et al. 2024). However, we found no convincing evidence that variation in this climate suitability bias explains the sporadic impact of the beetle. Hypothetical, non-climatic explanations include lack of suitable overwintering habitat, predation, and incompatible thistle control operations. We conclude that in general, climate suitability, while a necessary condition, is alone insufficient for the success of a classical weed biological control program, and that non-climatic habitat factors may explain patchy impacts of natural enemies such as C. rubiginosa.
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keywords
Californian thistle
CLIMEX
Tortoise beetle
Chrysomelidae
Asteraceae
Highlights
Cassida rubiginosa‘s impact on Cirsium arvense in NZ has been sporadic
Climate niche models reveal a climate suitability bias favouring the weed
Variation in the climate suitability bias does not explain the beetle’s sporadic impact