Comparing the contents, functions and neonicotinoid take-up between floral and extrafloral nectar within a single species (Hemerocallis citrina Baroni).

BACKGROUND AND AIMS: Many angiosperms can secrete both floral (FN) and extrafloral (EFN) nectar. However, much remains unclear about how EFN and FN differ in secretion, composition and ecological function, especially when both FN and EFN are secreted on flowers of the same species. METHODS: Hemerocallis citrina flowers secrete both FN and EFN. The FN and EFN traits including volume, presentation pattern and temporal rhythms of secretion were compared by field observation. Sugar and amino acid contents were analysed using regular biochemical methods, whereas the proteome was investigated by combined gel-based and gel-free approaches. Animal feeders on FN and EFN were investigated by field observation. Hemerocallis citrina plants were exposed by soil drenching to two systemic insecticides, acetamiprid and imidacloprid, and the concentration of these in FN and EFN was measured by ultra-high performance liquid chromatography coupled with mass spectrometry. KEY RESULTS: Hemerocallis citrina FN was concentrated and sucrose dominant, secreted in the mature flower tube and served as a reward for pollinators. Conversely, EFN was hexose rich, more dilute and less rich in sugar and amino acids. EFN was secreted on the outside of developing floral buds, and was likely to attract predatory animals for defence. EFN had fewer phenolics, but more pathogenesis-related components, such as chitinase and glucanase. A significantly different proteomic profile and enzymatic activities between FN and EFN suggest that they had different biosynthesis mechanisms. Both neonicotinoid insecticides examined became present in both nectar types soon after application, but in greater concentration within EFN; EFN also attracted a wider range of insect species than FN. CONCLUSIONS: Hemerocallis citrina FN and EFN differed in production, composition and ecological function. The EFN pathway could be a significant way for neonicotinoids to enter the wild food chain, and must be considered when evaluating the risks to the environment of other systemic insecticides.

Identification and quantitation of the novel insecticide sulfoxaflor and its metabolites in floral nectar from Salvia splendens Ker Gawl. (Lamiaceae).

Sulfoxaflor is a new systemic insecticide developed as a replacement for older neonicotinoids which are known to be toxic to pollinators. However, its metabolism in nectar and effect on nectar biosynthesis have not been investigated. After soil and foliar application, sulfoxaflor and its main metabolites in soil, leaf and Salvia splendens nectar, were measured by liquid chromatography coupled with triple quadrupole mass spectrometer (LC-MS/MS). The chemical composition between the clean and sulfoxaflor spiked nectar were also compared. The activities of two possible sulfoxaflor detoxifying enzymes in S. splendens nectar, nitrile hydratase and glutathione-s-transferase, were measured by LC-MS and spectrophotometry. S. splendens nectar proteome was investigated by high-resolution orbitrap-based MS/MS to screen for sulfoxaflor detoxifying relevant proteins. S. splendens could absorb sulfoxaflor through root or leaf surface and secrete a proportion of sulfoxaflor along with its metabolites into the nectar. After soil application, sulfoxaflor's low toxic metabolite X11719474 was dominant in the nectar and reached an average concentration of 8905 ppb. However, after foliar application, sulfoxaflor was dominant over its metabolites in the nectar. S. splendens nectar has no nitrile hydratase and glutathione-s-transferase activity and none of the 106 proteins identified in the nectar were predicted to function in detoxifying sulfoxaflor. Soil and foliar sulfoxaflor application can result in different profiles of sulfoxaflor and its metabolites presented in the nectar. However, sulfoxaflor had no effects on S. splendens nectar secretion and chemical composition and cannot be directly detoxified by components in the nectar.