Common St. John's wort (Malpighiales: Hypericaceae): an invasive plant in Maine wild blueberry production and its potential for indirectly supporting ecosystem services.
Common St. John's wort, Hypericum perforatum L. (Malpighiales: Hypericaceae), is a weed in Maine wild blueberry fields. A survey of its presence and relative density in 55 wild blueberry fields was conducted from 2013 to 2016. The objectives of this study were to determine how widespread it is as a weed in wild blueberry and whether it might indirectly contribute to beneficial ecosystem services for wild blueberry. It was found that St. John's wort occurs in about half (45.5%) of all wild blueberry fields surveyed. The crop cycle (prune vs cropping year) affected its relative abundance, significantly less St. John's wort was found in prune fields. St. John's wort relative abundance in wild blueberry fields was not affected by farming system (conventional vs organic) or landscape surrounding blueberry fields. Geographical distribution modeling was performed using the software Maxent. In Maine, the most likely areas predicted to be infested with St. John's wort were the two major blueberry production regions: Mid-coast and Downeast, Maine. Insects associated with St. John's wort were diverse. This weed appears to be under considerable herbivore pressure, especially hemipterans and Chrysolina spp. (Coleoptera: Chrysomelidae) beetles that have been released for biological control. Insect predators and parasitoids were abundant and may not only reduce herbivory on St. John's wort but may also provide a valuable ecosystem service in terms of predator spillover, resulting in reduction of wild blueberry insect pests. Bumble bees (Bombus spp., Hymenoptera, Apidae) are the most efficient pollinator of blueberry and were the predominant bee taxa found foraging on the flowers.