Introduced plants induce outbreaks of a native pest and facilitate invasion in the plants’ native range: Evidence from the emerald ash borer

1. Biological invasions are among the most serious threats to native
forest ecosystems worldwide due to ever-increasing international trade and
global change. Understanding the invasion processes and ecology of
invasive pests in both newly invaded and native habitats is necessary to
effectively manage the risks they pose. 2. The emerald ash borer (EAB),
Agrilus planipennis, is one of the most devastating invasive forest insect
pests in North America and has also invaded European Russia and parts of
Europe. Through synthesizing historical data spanning >100 years
and contemporary field observations in China, we examined EAB’s
distribution, occurrence, and outbreak frequency in its native range in
relation to historical introductions and plantings of non-Asian ash trees
in China. 3. The frequencies and levels of EAB infestations in China
gradually increased from 1900 to 2021 after a time-lag of 30-50 years
following introductions and widespread plantings of non-Asian ash trees
from North America. Increased frequencies of EAB outbreaks following the
planting of North American ash trees in China may have increased the risk
of EAB invading North America and other novel regions. 4. Synthesis. Our
findings demonstrated that planting susceptible non-native host plants can
induce outbreaks of a native insect pest in its native range, which in
turn may enhance risks of invading novel regions via human-assisted
activities (e.g., international trade). In addition, our findings suggest
that lag-times of several decades between planting susceptible hosts and
initial pest outbreaks may pose challenges in predicting the true risk of
invading novel regions. Consequently, comprehensive risk assessment for
invasive insect pests should consider the role of non-native plants
introduced or planted in the pest’s native range.