Identification of risk to kowhai, a New Zealand native plant Sophora microphylla Ait., from a potential biological control agent for broom, Cytisus scoparius (L.) Link

Abstract

Routine tests to determine the host specificity of the stem‐mining weevil, Pirapion immune, a potential biological control agent for broom, Cytisus scoparius, indicate that kowhai, Sophora microphylla, is a possible alternative host plant. Many more weevils were reared successfully on C. scoparius (x = 65.8) than on S. microphylla (x = 0.8), and significantly more eggs were laid on C. scoparius than on S. microphylla. However, most females laid eggs on both species in choice tests. Field tests in Europe also showed that weevils given equal access to both plant species used both species. P. immune has been rejected as a potential control agent for C. scoparius in New Zealand. Plants within the genus Sophora should be tested carefully for potential risk from any proposed introduction for control of weeds within the tribe Genisteae.

Key words:

• Pirapion immune
• Coleoptera
• Curculionidae
• Fabaceae
• Genisteae
• Sophoreae
• Sophora microphylla
• kowhai
• Cytisus scoparius
• broom
• host specificity
• biological control
• risk factors