From an April 11 article in the Cornell Chronicle by Krishna Ramanujan, Poor plant defenses promote invasive beetle’s success, not lack of predators.
While most researchers attribute invasive species’ success to a lack of natural predators in their new territory, Cornell researchers offer proof for a less popular explanation: Invasive species fare so well because host species lack an evolutionary history with — and defenses against — the new invaders.
Their study examined the relationship between the viburnum leaf beetle (Pyrrhalta viburni), which originated in Europe and was first discovered in North America in 1924, and viburnums, common woody shrubs found in gardens and forests, with native species in North America, South America, Asia and Europe. There were at least three events, millions of years ago, where Eurasian viburnums colonized North America. During each of those events, a single colonization diversified into several North American species, but without a predatory beetle putting adaptive pressures on them.
Meanwhile, European viburnums continued to evolve with such beetles and developed a defense strategy: The female beetle lays her eggs in twigs in summer, but they don’t hatch until the following spring. During that time, the twig tissue of European viburnums grows over the eggs and crushes them. In North American species, this defense is greatly reduced.
Viburnum eggs hatch and larvae start feeding in late April or early may in most of New York. Visit the Viburnum Leaf Beetle Citizen Science website for more information about how to identify and manage this pest.