title: Consequences of toxic secondary compounds in nectar for mutualist bees and antagonist butterflies.
abstract: Attraction of mutualists and defense against antagonists are critical challenges for most organisms and can be especially acute for plants with pollinating and non-pollinating flower visitors. Secondary compounds in flowers have been hypothesized to adaptively mediate attraction of mutualists and defense against antagonists, but this hypothesis has rarely been tested. The tissues of milkweeds (Asclepias spp.) contain toxic cardenolides that have long been studied as chemical defenses against herbivores. Milkweed nectar also contains cardenolides, and we have examined the impact of manipulating cardenolides in nectar on the foraging choices of two flower visitors: generalist bumble bees, Bombus impatiens, which are mutualistic pollinators, and specialist monarch butterflies, Danaus plexippus, which are herbivores as larvae and ineffective pollinators as adults. Although individual bumble bees in single foraging bouts showed no avoidance of cardenolides at the highest natural concentrations reported for milkweeds, a pattern of deterrence did arise when entire colonies were allowed to forage for several days. Monarch butterflies were not deterred by the presence of cardenolides in nectar when foraging from flowers, but laid fewer eggs on plants paired with cardenolide-laced flowers compared to controls. Thus, although deterrence of bumble bees by cardenolides may only occur after extensive foraging, a primary effect of nectar cardenolides appears to be reduction of monarch butterfly oviposition.
authors.affiliation: Department of Ecology and Evolutionary Biology, Cornell University, Corson Hall, 215 Tower Road, Ithaca, New York, 14853, USA.
authors.forename: Patricia L
authors.initials: PL
authors.lastname: Jones
authors.affiliation: Department of Ecology and Evolutionary Biology, Cornell University, Corson Hall, 215 Tower Road, Ithaca, New York, 14853, USA.|Department of Entomology, Cornell University, Corson Hall, 215 Tower Road, Ithaca, New York, 14853, USA.
authors.forename: Anurag A
authors.initials: AA
authors.lastname: Agrawal
mesh_terms: D000818:Animals; D031108:Asclepias; D001516:Bees; D002080:Butterflies; D005260:Female; D006790:Host-Parasite Interactions; D010058:Oviposition; D057048:Plant Nectar / Q000633:toxicity*
chemical_list: D057048:Plant Nectar
keywords: cardiac glycoside; egg laying; flower constancy; learning; nectar foraging; plant-insect interactions; toxic nectar