Clipping the butterfly bush's wings: defoliation studies to assess the likely impact of a folivorous weevil

摘要

Predicting agent success is a topic that has attracted much attention from the biological control community. Although the likely success of agents establishing in a new environment remains elusively unpredictable, we can often gain an impression of the likely nature of the agent's impact in different environments should it establish in reasonable numbers. The butterfly bush, or buddleia (Buddleja davidii Franch.), is a major weed problem in many regions with temperate or Mediterranean climates and has been identified as the highest priority for biological control in Europe. In New Zealand, it has invaded disturbed sites such as plantation forest coups, roadsides, earth slips and gravel river beds. To combat buddleia in New Zealand, a biological control programme was commenced around 1990. Whilst host-specificity testing was being completed on Cleopus japonicus Wingelmtiller, a leaf-feeding weevil, defoliation experiments were undertaken to assess its likely impact on the growth and survival of itsprime host, buddleia. Seasonal defoliation studies revealed that in the absence of plant competition, buddleia was quite resilient and able to recover rapidly from severe defoliation. Experiments with plant competition, leaf consumption rates and insectdevelopments rates were used to develop a model to explore the likely impact of C. japonicus.