Combined secondary compounds naturally found in nectars enhance honeybee cognition and survival

Abstract

The alkaloid caffeine and the amino acid arginine are present as secondary compounds in nectars of some flower species visited by pollinators. Each of these compounds affects honeybee appetitive behaviors by improving its foraging activity and learning. While caffeine potentiates responses of mushroom body neurons involved in honeybee learning processes, arginine acts as precursor of nitric oxide enhancing the protein synthesis involved in memory formation. Despite existing evidence on how these compounds affect honeybee cognitive abilities individually, the effect of their mixtures on this matter is still unknown. We evaluated acquisition and memory retention in classical olfactory conditioning procedure, in which reward (sucrose solution) contained traces of caffeine, arginine or mixtures of both. The results indicate that the presence of the single compounds and their most concentrated mixture increases bees’ learning performance. However, memory retention, measured at short- and long-term, increases significantly only in those treatments offering mixtures in the reward. Additionally, the most concentrated mixture triggers a significant survival rate in the conditioned bees. Thus, some nectar compounds, when combined, show synergistic effects on cognitive abilities and survival in an insect.

Learning of a mimic odor combined with nectar nonsugar compounds enhances honeybee pollination of a commercial crop

“…Apart from higher activity at the colony, higher densities of honeybee foragers were found on sunflowers in the surroundings of colonies fed SM + Mix, regardless of the parental line, denoting the activation of foraging towards the target crop. Such results agree with the positive effect of these two compounds jointly administered on memory retention of conditioned honeybees under laboratory conditions 33 . In the mentioned study, the mixture of both NSC (in the same concentrations as considered herein) improved short and long-term olfactory memories, tested 15 min and 24 h after conditioning restrained bees.…”

“…On the one hand, while caffeine has been shown to enhance the activation of mushroom body neurons involved in high-order memory formation processes 23 , the oxidation of arginine produces NO, which in turn participates in LTM processes (≥ 1 day) 30 , 31 , 34 . On the other hand, while the consumption of caffeinated nectar has been shown to activate foraging responses within a few hours 24 , one would expect a deferred effect of arginine consistent with NO-dependent LTM processes and with previous results showing that the administration of arginine in the sucrose reward was not enough to enhance memory retention by 24 h, though the combined action of both NSC did 33 . Although further studies are needed to thoroughly understand the underlying mechanisms of the interaction of these two compounds, our results show a clear effect of their combination across all variables measured.…”

“…The synthetic mixture (Sunflower mimic) is composed by sabinene (48%), (−)-beta-pinene (40%) and limonene (12%) 42 . The concentrations of caffeine and arginine considered are within or below the natural range found in nectars 33 . These authors found that such concentrations (see section below) positively affected olfactory memories in honeybees without compromising their survival.…”

“…Despite the co-occurrence of a wide variety of NSC in floral nectars, few studies have investigated the effect of mixtures in pollinator behavior 19 . The oral administration of caffeine and arginine, presented in combination and in concentrations within or below the natural range found in nectars, has recently been reported to have a positive effect in the memory formation processes, improving short and long-term olfactory memory retention in conditioned bees under laboratory conditions 33 . Additionally, this mixture triggered a significant survival rate in the conditioned bees.…”

Discovery of octopamine and tyramine in nectar and their effects on bumblebee behavior

“…Despite nectar’s chemical diversity ( Palmer-Young et al., 2018 , 2019 ), our understanding of its effects on pollinators is limited in two key ways. First, though foliar chemical ecology highlights the relevance of synergistic effects ( Richards et al., 2016 ), research on the behavioral effects of nectar chemistry typically involves a small number of phytochemicals studied in isolation ( Adler, 2000 ; Stevenson et al., 2017 ), but see Estravis-Barcala et al., 2021 ; Hernández et al., 2018 ; Marchi et al., 2021 ; Richman et al., 2022 ; Thorburn et al., 2015 ). Secondly, though insect hormones and endocrine disruptors have long been identified in leaf tissues ( Bowers, 1991 ), whether nectar is a site of any analogous chemical “cross-talk” between plants and pollinators (as explored for floral volatiles by Schiestl, 2010 ) is an obvious question ( Mustard, 2020 ; Schultz and Appel, 2004 ).…”