Direct and Indirect Impacts of the Tuberolachnus salignus (Hemiptera: Aphididae) Invasion in New Zealand and Management Alternatives

Invasive insects are a serious problem in New Zealand, and their introduction and successful establishment are predicted to increase with global commerce and climate change. A recent introduction to New Zealand is Tuberolachnus salignus (Gmelin), a large aphid that attacks mainly willows but also other plants such as poplars, apples, and pears. It was first reported in 2013 but has since then spread rapidly throughout the country. We conducted a 2-yr study exploring the direct (on the host plant) and indirect (on other organisms) impacts of the aphid, in a field setting including 15 willow clones selected to represent the variety of species and hybrids present in New Zealand. Our research revealed great variation in the level of resistance/susceptibility of different clones and suggested a trade-off between reproduction, growth, and defense. We investigated the indirect effects of the aphid on honeydew foragers and on the soil ecosystem, through honeydew production and deposition, revealing complex cascading effects involving multiple trophic levels. We also explore and discuss management alternatives including the replacement of willows for native species or resistant varieties, the use of biological control agents, and the feasibility of chemical control. This work is one of few studies on the complex ecological effects of invasive phytophagous insects and could serve as a model for future research and to inform pest management. To conclude, we identify gaps in the knowledge and highlight aspects requiring further research.