Damage Levels from Arthropod Herbivores on Lonicera maackii Suggest Enemy Release in its Introduced Range

The ‘enemy release hypothesis’ argues when a species is introduced to a novel habitat, release from regulation by herbivores results in increased vigor, abundance, and distribution. The invasive Asian shrub Lonicera maackii appears to benefit from an absence of arthropod herbivores in North America. We assessed the incidence, amount, and type of herbivory occurring on L. maackii in forest edge and interior habitats and investigated differences in timing of damage. In October 2008, leaves were sampled from shrubs in forest interior and edge habitat from 8 sites in Ohio. In 2009, sampling was repeated at 3 sites in spring, summer, and fall with a distinction made between long and short branches. Leaf area removed averaged 1.83% across the 8 populations in 2008 and 3.09% across the 3 populations in 2009, with forest edge plants receiving slightly more damage than forest interior plants in 2008. Additionally, long shoots received more damage than short shoots in 2009. Damage incidence was also higher in the edge habitat and on long shoots compared to short shoots. As measured in 2009, damage accumulated steadily throughout the season. Chewing was the most prevalent type of damage (76. 8%) and low level of pathogen infection was observed (4.81%). Results indicate that levels of herbivory experienced by L. maackii are relatively consistent across sites, vary slightly with habitat and branch identity, but are likely too low to impact fitness of shrubs. These findings indicate that low amounts of arthropod herbivory occur for L. maackii across its introduced range, which may contribute to its invasive success