Novel plant–insect interactions in an urban environment: enemies, protectors, and pollinators of invasive knotweeds

Abstract

Relationships between invasive plants and other species in their introduced ranges may facilitate or hinder the process of invasion. Fallopia japonica (Japanese knotweed), Fallopia sachalinensis (giant knotweed), and their hybrid Fallopia 9 bohemica (Bohemian knotweed) are widespread invasive plants in North America and Europe. These species possess extrafloral nectaries (EFNs) that attract mutualist insect protectors in their native ranges. Popillia japonica Newman, 1841 (Japanese beetle) is a primary herbivore of invasive Fallopia spp. in these species' native range in Japan. These natural enemies are reunited in North America, where Fallopia spp. have been repeatedly introduced as ornamental plantings of residential and commercial properties since the 1800s, and the Japanese beetle has become a widespread insect pest. Spread of Fallopia spp. and their hybrids along linear features of urban landscapes such as roads, railways, and waterways make their performance in urban environments important to these invasive species' impact. To test the role of insect interactions in the success of Fallopia japonica and F. 9 bohemica in urban conditions in their invasive range, we examined ant visitation, Japanese beetle abundance and herbivory, ant-Japanese beetle interactions, pollinator visits, and seed production. All active herbivory observed was by Japanese beetles. Leaf area loss to herbivory was much lower than levels reported in Japan, suggesting partial enemy release. New Fallopia leaves were more frequently visited by ants than mature leaves, while Japanese beetle herbivory was observed on mature but not on new leaves. All ant species observed visiting invasive Fallopia EFN were native to North America. Active physical defense by these ants against Japanese beetles was observed but was rare. Native and non-native insects visited Fallopia flowers, followed by seed production. Our results indicate that both native and non-native species may facilitate invasion of Fallopia through pollination and protection mutualisms.

Patterns of population genomic diversity in the invasive Japanese knotweed species complex

“…Despite the fact that the individuals sampled in this study were predominantly female, nearly all plants effectively filled seeds. Native pollinators are active and effective in R. japonica populations (Johnson et al, 2019), though the exact routes of pollen are not completely clear. The resulting seeds are highly germinable, and the seedlings can establish in natural settings (Forman and Kesseli, 2003), so it seems likely that in addition to clonal spread, sexual reproduction is occurring in North American populations.…”

Invasive plants as biosorbents for environmental remediation: a review

“…Washing biomass not only removes the impurities, pathogen borne agents but also discards some endogenic inorganics that affect the adsorption process. Johnson et al (2019) identified fourteen species of insects including ant, fly, wasp, bee, and beetle that were considered the visitors of exotic weed Fallopia japonica. Many of them were proved to be vectors transmitting pathogens during plant-insect interactions.…”

Be(e)coming pollinators: Beekeeping and perceptions of environmentalism in Massachusetts

“…Many of the species brought to America—including honey bees and many plants—were indigenous to the general region surrounding Europe, the Middle East, and Asia [ 126 , 130 – 132 ]. When honey bees and introduced plants are from similar geographic regions, these plant species are more likely to be effectivity pollinated by honey bees than by the native bees of new landscapes [ 68 , 133 , 134 ].…”