Detection of Iridoids in Snapdragons and Methods to Observe Effects of Toxic Nectar on Pollination Behavior of Bumblebees
Smith, Nicholas C.
MetadataShow full item record
Plants produce an array of secondary defense compounds that are toxic or deterrent to herbivores and microbial pathogens. The role of secondary compounds in plants as defense agents against herbivores is clearly established. Production of secondary compounds increases following wounding from herbivores. Defense compounds have also been reported in nectar from many flowering plant families, leading to the term ‘toxic nectar’ to describe such nectar. At first glance, toxic nectar appears counteradaptive because nectar rewards pollinators in exchange for pollination. In this study, we sought to examine the role of iridoids, a type of secondary defense compound, in nectar of the common snapdragon, Antirrhinum majus (family Plantaginaceae) by assessing iridoid content in plant tissue and quantifying the effect of toxic nectar on visitation behavior of the bumblebee Bombus impatiens, a snapdragon pollinator. We used high performance liquid chromatography (HPLC) to analyze plant tissue for iridoids and designed three experiments to test bee responses to toxic nectar. We confirmed the presence of iridoids in leaf and floral tissues but were unable to extract sufficient nectar for analysis. Application of jasmonic acid, a plant hormone released in response to wounding, did not increase iridoid levels in plant tissue. Attempts to measure bee responses to manipulated nectar were unsuccessful. Despite the use of outdoor and indoor enclosures, captive and wild bees, and natural and artificial flowers, bees would not forage. The presence and function of secondary compounds in snapdragon nectar remains unresolved. We suggest improvements for future experimental designs to answer these questions.