Effect of amino acid enriched diets on hemolymph amino acid composition in honey bees.

Amino acids (AAs) are an abundant class of nectar solutes, and they are involved in the nectar attractiveness to flower visitors. Among the various AAs, proline is the most abundant proteogenic AA, and γ-amino butyric acid (GABA) and ß-alanine are the two most abundant non-proteogenic AAs. These three AAs are known to affect insect physiology, being involved in flight metabolism and neurotransmission. The aim of this study was to investigate the effects of artificial diets enriched with either ß-alanine, GABA, or proline on consumption, survival, and hemolymph composition in honey bees belonging to two different ages and with different metabolism (i.e., newly emerged and foragers). Differences in feed intake among diets were not observed, while a diet enriched with ß-alanine improved the survival rate of newly emerged honey bees compared to the control group. Variations in the hemolymph AA concentrations occurred only in newly emerged honey bees, according to the diet and the time of hemolymph sampling. A greater susceptibility of young honey bees to enriched diets than older honey bees was observed. The variations in the concentrations of hemolymph AAs reflect either the accumulation of dietary AAs or the existence of metabolic pathways that may lead to the conversion of dietary AAs into different ones. This investigation could be an initial contribution to studying the complex dynamics that regulate hemolymph AA composition and its effect on honey bee physiology.

Secondary Metabolites in Nectar-Mediated Plant-Pollinator Relationships.

In recent years, our understanding of the complex chemistry of floral nectar and its ecological implications for plant-pollinator relationships has certainly increased. Nectar is no longer considered merely a reward for pollinators but rather a plant interface for complex interactions with insects and other organisms. A particular class of compounds, i.e., nectar secondary compounds (NSCs), has contributed to this new perspective, framing nectar in a more comprehensive ecological context. The aim of this review is to draft an overview of our current knowledge of NSCs, including emerging aspects such as non-protein amino acids and biogenic amines, whose presence in nectar was highlighted quite recently. After considering the implications of the different classes of NSCs in the pollination scenario, we discuss hypotheses regarding the evolution of such complex nectar profiles and provide cues for future research on plant-pollinator relationships.

Rice Byproduct Compounds: From Green Extraction to Antioxidant Properties.

Currently, rice (Oryza sativa L.) production and consumption is increasing worldwide, and many efforts to decrease the substantial impact of its byproducts are needed. In recent years, the interest in utilizing rice kernels, husk, bran, and germ for the recovery of different molecules, from catalysts (to produce biodiesel) to bioactive compounds, has grown. In fact, rice byproducts are rich in secondary metabolites (phenolic compounds, flavonoids, and tocopherols) with different types of bioactivity, mainly antioxidant, antimicrobial, antidiabetic, and anti-inflammatory, which make them useful as functional ingredients. In this review, we focus our attention on the recovery of antioxidant compounds from rice byproducts by using innovative green techniques that can overcome the limitations of traditional extraction processes, such as their environmental and economic impact. In addition, traditional assays and more innovative methodologies to evaluate the antioxidant activity are discussed. Finally, the possible molecular mechanisms of action of the rice byproduct antioxidant compounds (phenolic acids, flavonoids, γ-oryzanol, and vitamin E) are discussed as well. In the future, it is expected that rice byproduct antioxidants will be important food ingredients that reduce the risk of the development of several human disorders involving oxidative stress, such as metabolic diseases, inflammatory disorders, and cancer.

Effects of Non-Protein Amino Acids in Nectar on Bee Survival and Behavior.

Nectar mediates complex interactions between plants and animals. Recent research has focused on nectar secondary compounds that may play a role in regulating some of these interactions. These compounds may affect the behavior of nectar feeders by interacting with their neurobiology. Non-protein amino acids (NPAAs) can constitute a large portion of the amino acid content of floral nectar, but their ecological function has, to date, not been investigated. In this study, we tested the effects of diets with low and high concentrations of γ-amino butyric acid (GABA) and ß-alanine on the survival and behavior of Bombus terrestris and Apis mellifera. The most apparent effect on longevity was observed for B. terrestris workers that fed on high concentration of GABA, with longevity increased. By contrast, neither of the two NPAAs (at either concentration) had an affect on A. mellifera longevity. At the low NPAA concentration, only B. terrestris workers showed a difference in consumption, consuming more ß-alanine solution than the other two solutions. By contrast, at the high NPAA concentration, only A. mellifera workers showed a difference in consumption, consuming more ß-alanine solution. The effects of the NPAAs on behavior differed between the two species, with B. terrestris appearing more sensitive to the NPAAs than A. mellifera. After consuming NPAAs, B. terrestris showed changes in three (walking, flying, stationary) of the four behaviors recorded, although the effects varied with concentration and compound. In contrast, honey bees only showed a change in feeding behavior, with consumption of both NPAAs (at low concentrations) resulting in a decrease. Thus, pollinator intake of NPAAs may have important behavioral/ecological implications.

Distasteful Nectar Deters Floral Robbery.

Toxic nectar is an ecological paradox [1, 2]. Plants divert substantial resources to produce nectar that attracts pollinators [3], but toxins in this reward could disrupt the mutualism and reduce plant fitness [4]. Alternatively, such compounds could protect nectar from robbers [2], provided that they do not significantly alter pollinator visitation to the detriment of plant fitness [1, 5-8]. Indeed, very few studies have investigated the role of plant toxins in nectar for defense against nectar robbers [4, 9, 10]. Here, we compared two Aconitum species (A. napellus and A. lycoctonum) that have flowers specialized for long-tongued bumblebee pollinators (Bombus hortorum) but are occasionally robbed by short-tongued bumblebees (B. terrestris) [6, 11-13]. Pollinator visits to flowers were much more frequent than by robbers, but visits correlated negatively with nectar alkaloid concentration and declined sharply between 200 and 380 ppm. However, alkaloid concentrations of >20 ppm were deterrent to B. terrestris, suggesting that robbers were less tolerant of nectar alkaloids. Nectar of both plant species contained similar concentrations of carbohydrates and toxic alkaloids, but A. lycoctonum was more likely to secrete nectar in each flower and was also visited more frequently by pollinators and robbers. We conclude that alkaloids in Aconitum spp. nectar affect rates of both pollinator visitation and robbery but may have co-evolved with nectar availability to maintain the fitness benefits of specialized plant-pollinator relationships. Chemical defense of nectar is, however, ultimately constrained by pollinator gustatory sensitivity.