Impact of Insecticide Treatment on Herbivory and Reproductive Success of the Federally Endangered Plant Clematis morefieldii Kral

ABSTRACT Herbivory is common on the federally endangered Clematis morefieldii (Ranunculaceae), but little is known about its effect on reproductive output. Over 3 yr, we applied the insecticide Sevin (0.26% carbaryl) or water (as a control) to 40 plants (20 per treatment) every 3 wk during the growing season. Herbivores destroyed fewer flower buds on insecticide-treated plants (18.4% fewer in 2010, 45.6% fewer in 2011, 39.7% fewer in 2012), but fruit production increased 3.7- fold on insecticide-treated plants only in 2011. High rainfall during peak flowering/fruiting (April– June) influenced the effectiveness of treatments by boosting achene production in 2011. We compared the amounts of vegetative herbivory (vertebrate browse damage, invertebrate browse damage, piercing-sucking herbivore damage, or leaf miner damage) within each year. Both vertebrate and invertebrate browse damage were significantly greater (1.2- to 2.2-fold) on control plants for all three years. Piercing-sucking herbivory was greater (25–40% more) on control plants during most of the growing season for all three years. Vertebrate damage was more frequent on insecticide-treated plants (25–40% greater) during 2012. During high rainfall years, invertebrate herbivory reduced reproductive output, either directly by attacking flower buds/flowers or indirectly by vegetative herbivory that reduces resources available for reproduction. Insecticide use during years of high insect infestation could be a viable option for managers seeking to increase seed output by this rare plant.