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

Abstract

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. 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 proteome was investigated by combined gel-based and gel-free approaches. FN and EFN animal feeders were investigated by field observation. H. citrina plants were exposed by soil drenching to two systemic insecticides, acetamiprid and imidacloprid, and the concentration of these in FN and EFN were measured by ultra-high performance liquid chromatography coupled with mass spectrometry. Key Results H. 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 less phenolics, but more pathogenesis-related components, such as chitinase and glucanase. 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 H. 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.

Effects of sub‐nanogram doses of acetamiprid, dimethoate, flupyradifurone, and sulfoxaflor on courtship, mating, and olfactory host finding of the parasitic wasp Lariophagus distinguendus

“…Little is known about the occurrence of L. distinguendus outside human grain and food stores, but according to Graham (1969) it is also found in open country, where it might get into contact with contaminated floral and extrafloral nectar, honeydew, or guttation water all of which have been shown to be consumed by parasitic wasps (Jervis et al., 1993; Idris & Grafius, 1995; Röse et al., 2006; Wanner et al., 2006; Urbaneja‐Bernat et al., 2020). All these fluids may contain pesticide residues and may thus function as carriers of these substance to parasitic wasps (Davis et al., 1988; Schmolke et al., 2018; Zhou et al., 2022). The doses for topical application used in the present study were chosen according to their acute toxicity (causing <30% mortality) and most of them were in fact sublethal.…”