Mechanisms of Success: Plant-Herbivore Interactions and the Invasion of Non-native Lonicera Species in North America

Invasion by non-native species is a complicated process and many hypotheses have been proposed to explain how invasive plant species are often poor competitors in their native range, but dominant in their novel range including the enemy release and novel weapons hypotheses. Additionally, many invasive species are characterized as being tolerant and/or resistant to both damage and limitations in abiotic resources. These hypotheses are based on plant-plant, plant-microbial, and plant-herbivore interactions in the invaders novel range and are not mutually exclusive. The genus Lonicera (Caprifoliaceae) includes approximately 200 species worldwide, with 18 native and 16 introduced species in North America. Some Asiatic species like Lonicera maackii, L. tatarica, and L. japonica are particularly successful invaders in North America, while North American natives are relatively uncommon or not abundant where they are found. I investigated the plant-insect interactions and defensive strategies of non-native Lonicera species, with particular focus on L. maackii in Ohio. I first quantified the amounts of arthropod herbivore damage occurring on L. maackii across two seasons. I expanded this assessment to include a co-occurring native congener L. reticulata and the confamiliar Viburnum prunifolium. Additionally, I included feeding bioassays to assess the performance of a specialist and generalist herbivore on native and non-native Lonicera species. Tolerance of mature shrubs was evaluated through measures of growth responses after repeated clipping. Greenhouse experiments with real and simulated herbivory were completed to determine the tolerance of juvenile L. maackii plants to herbivory and how this may be affected by changes in resource availability. Resistance traits were also evaluated in this experiment through measures of secondary metabolites with and without herbivory. Finally, resistance traits were further evaluated through a common garden experiment including multiple native and non-native Lonicera species, where herbivore damage, generalist herbivore performance, and both qualitative and quantitative analyses of defensive chemistry were evaluated in high and low nutrient treatments. Lonicera maackii and other non-native Lonicera species receive insignificant amounts of arthropod herbivore damage in the field and the damage they receive is much less than amounts incurred on native Lonicera and confamiliar V. prunifolium. Mature L. maackii shrubs are highly tolerant to large amounts of simulated herbivore damage, juvenile L. maackii is both tolerant and resistant to high amounts of real and artificial damage, and limiting light and soil nutrients did not limit their ability to tolerate herbivory. A honeysuckle specialist avoids L. maackii in the field, but can develop on L. maackii in the laboratory. Plants in the Lonicera genus that display resistance to arthropod herbivores can be characterized as being chemically well defended, and are generally poor hosts to generalist herbivores. Although native/non-native origin did not explain the chemical profiles of species, native Lonicera tended to produce more iridoid glycosides and non-native Lonicera produced more phenolic compounds. Lonicera maackii and other non-natives appear to not only escape damage from arthropod herbivores, they are also able to tolerate and resist the damage they do incur suggesting that a combination of mechanisms contribute to the success of these non-native Lonicera in North America