Background/Question/Methods Selenium (Se) contamination from agricultural irrigation and runoff has caused the buildup of toxic levels of selenate (Se⁺⁶) in water and soil across the western U.S., particularly in the central valley of California. In these contaminated areas, insect pollination can be critical to the functioning of both agricultural and natural ecosystems, yet we know very little about how pollutants such as Se can impact pollination ecology.  We tested the hypothesis that Se will accumulate in the pollen and nectar of two plant species and negatively affect floral traits and plant reproduction. Brassica juncea (L.) Czern (Indian mustard) and Stanleya pinnata (Pursh) Britton (Desert Prince’s Plume) are used for phytoremediation of Se contaminated soils and are both foraged upon by honeybees as well as other pollinators. Plants were grown in the greenhouse using an irrigation tank system and were watered with concentrations of 1.5 and 3.0 mg/L sodium selenate (Na₂SeO₄).  Plants irrigated with 0.0 mg/L Na₂SeO₄ served as controls.
Results/Conclusions  Brassica juncea and S. pinnata plants irrigated with 3.0 ppm Na₂SeO₄ produced pollen that contained 669.40 ± 45.35 µg Se/g and 1866.27 ± 577.62 µg Se/g dry weight (respectively).  Brassica juncea and S. pinnata nectar contained 108.90 ± 40.76 µg Se/ml and 140.99 ± 44.23 µg Se/ml. Both plant species produced pollen and nectar that contained Se concentrations higher than the LC₅₀ value (21.4 µg Se/g) for an herbivore. Se treatments significantly impacted floral traits in B. juncea (ANOVA, P < 0.0031) but not S. pinnata (P > 0.2441), a Se hyperaccumulator. Se accumulation also reduced seed pod length in B. juncea (P = 0.0042) and may also impact seed production.  Se uptake by non-hyperaccumulator plants (such as B. juncea) may negatively alter floral traits, rendering them unattractive to pollinators or even reducing pollen deposition and reproduction.  Se accumulation in leaf tissues reduces the fitness of several types of herbivores, but there are currently no studies to date examining the effects of floral tissues containing Se on pollinator fitness.  If pollinators cannot detect and avoid toxic Se compounds in the plant tissues they are foraging upon and collecting for their progeny, they may suffer similar adverse effects to those reported in other insect guilds.