Compounds In Nectar Research Articles

High Concentration of Nectar Quercetin Enhances Worker Resistance to Queen’s Signals in Bees

In honeybee colonies, pheromones produced by the host's queen inhibit worker reproductive potential and queen rearing. Here, we showed that worker bees fed with syrup containing high concentrations of the phenolic quercetin are likely to initiate ovarian development and to build many queen cells in their colony throughout the feeding trial. Workers fed syrup containing high levels of quercetin were aggressive against their queen. Our study suggests that increased phenolic compounds in nectar could enhance worker bee resistance to queen signals in honeybee colonies.

The Effect of Larval Diet and Sex on Nectar Nicotine Feeding Preferences in Manduca Sexta (Lepidoptera: Sphingidae)

Many Lepidoptera interact with the same plant species as both herbivorous larvae and nectar-feeding adults (Adler & Bronstein 2004), providing the potential for plant secondary compounds to influence both pollination and herbivory through expression in floral and foliar tissue. Secondary compounds in nectar may be costly to plants if they deter pollinators, but beneficial if they deter oviposition of herbivorous offspring. Several studies have examined how pollinators respond to secondary compounds in nectar (Detzel & Wink 1993; Adler 2000; Liu et al. 2004; Tadmor-Melamed et al. 2004; Adler & Irwin 2005; Singaravelan et al. 2005; Kessler & Baldwin 2007). However, foraging responses can vary between individuals due to several factors, including sex and previous experience. For example, female insects often require amino acids for egg maturation (Jervis et al. 2005), so sexes may differ in foraging criteria. Larval experience could also influence adult oviposition (e.g., Hopkin's host selection principle, Barron 2001). We asked how sex and larval exposure to nicotine affected adult feeding and oviposition in response to nicotine in nectar. Manduca sexta L. (Lepidoptera: Sphingidae) is a larval specialist herbivore on solanaceous plants including Nicotiana species (e.g., Madden & Chamberlin 1945; Lou & Baldwin 2003), and non-nicotine species such as tomato (Chen et al. 2005). Thus, some larvae consume nicotine while others do not. Several Nicotiana species have nicotine in nectar (Detzel & Wink 1993; Raguso et al. 2003; Adler et al. 2006; Kessler & Baldwin 2007). First instars of M. sexta (North Carolina State University Insectary) were placed in individual 170-g cups with plastic lids and randomly assigned to no-nicotine or nicotine treatments (n = 177 and 173) with synthetic diet (F9783B, Bioserv, Inc. Frenchtown, NJ, USA) with or without 2% incorporated nicotine by wet weight ((-) nicotine, Sigma-Aldrich, Inc. N3876), well within the range in tobacco plants (Sisson & Severson 1990). Larvae were provided fresh diet ad libitum and allowed to pupate. We recorded mortality, time to pupation, pupal weight, and sex for each individual. Pupae were then divided into 4 greenhouse (9.5:14.5 L:D, temperature 25-26°C) cages (55-61 cm3) by larval diet treatment and sex. After emergence, moths were marked on their forewings to indicate larval diet treatment and sex, and transferred to a holding cage for mating and feeding. We measured moth feeding preferences with artificial flowers (Kinko's gray fleck paper, Goyret & Raguso 2006) with 3 nectar compositions: high (0.0005% nicotine; 5 ppm), low (0.0001% nicotine; 1 ppm), and no nicotine. Flowers were placed into 1.5-mL microcentrifuge vials containing 0.5-mL of synthetic nectar without touching the nectar. Nectar was made from a 14% sugar solution (2:1:1 ratio of sucrose: glucose: fructose) to match the sucrose equivalents of AT. tabacum nectar (Adler, unpublished data) and the ratio of sugars in other Nicotiana species (Kaczorowski et al. 2005). Nicotine concentrations were based on levels in N.

Whitebellied sunbirds (Nectarinia talatala, Nectariniidae) do not prefer artificial nectar containing amino acids

Amino acids are the most abundant class of compounds in nectar after sugars. Like its sugar concentration, the amino acid concentration of nectar has been linked to pollinator type, and it has been suggested that amino acid concentrations are high in the floral nectars of plant species pollinated by passerine birds compared to those pollinated by hummingbirds. We investigated the feeding response of whitebellied sunbirds (Nectarinia talatala) to the inclusion of amino acids in artificial nectar (0.63 M sucrose solution). The response to asparagine, glutamine, phenylalanine, proline, serine and valine, amino acids commonly found in floral nectars, was tested individually and using a mixture of all six amino acids, at two different concentrations (2 and 15 mM). Sunbirds showed no significant preference for amino acids in nectar, or avoided them, especially at the higher concentration. We discuss these findings in the light of the nitrogen requirements of nectarivorous birds and data on amino acids in floral nectars.

Adaptive functions of defensive plant phenolics and a non‐linear bee response to nectar components

Summary 1Secondary compounds such as phenolics, usually present in floral nectar, may act in combination with sugar components to influence the evolution of pollination mutualism. 2Previous work on the significance of secondary compounds in nectar considers honey bee responses to those compounds alone, but neglects sugar. Our experiments demonstrated that phenolic sugar syrups were attractants to free-flying Asian Apis cerana Fab. when sugar concentrations were 15–35%, but were deterrents below or above this range. 3Synergism between nectar phenolics and sugar may thus provide a novel mechanism for plants to encourage pollinating bees and reduce energy investment in nectar, operating as exaptations by co-opting defence mechanisms against herbivores.

Leaf herbivory and nutrients increase nectar alkaloids

Correlations between traits may constrain ecological and evolutionary responses to multispecies interactions. Many plants produce defensive compounds in nectar and leaves that could influence interactions with pollinators and herbivores, but the relationship between nectar and leaf defences is entirely unexplored. Correlations between leaf and nectar traits may be mediated by resources and prior damage. We determined the effect of nutrients and leaf herbivory by Manduca sexta on Nicotiana tabacum nectar and leaf alkaloids, floral traits and moth oviposition. We found a positive phenotypic correlation between nectar and leaf alkaloids. Herbivory induced alkaloids in nectar but not in leaves, while nutrients increased alkaloids in both tissues. Moths laid the most eggs on damaged, fertilized plants, suggesting a preference for high alkaloids. Induced nectar alkaloids via leaf herbivory indicate that species interactions involving leaf and floral tissues are linked and should not be treated as independent phenomena in plant ecology or evolution.

ECOLOGICAL COSTS AND BENEFITS OF DEFENSES IN NECTAR

The nectar of many plant species contains defensive compounds that have been hypothesized to benefit plants through a variety of mechanisms. However, the relationship between nectar defenses and plant fitness has not been established for any species. We experimentally manipulated gelsemine, the principal alkaloid of Carolina jessamine (Gelsemium sempervirens), in nectar to determine its effect on pollinator visitation, nectar robber visitation, and male and female plant reproduction. We found that nectar robbers and most pollinators probed fewer flowers and spent less time per flower on plants with high compared to low nectar alkaloids. High alkaloids decreased the donation of fluorescent dye, an analogue of pollen used to estimate male plant reproduction, to neighboring plants by one-third to one-half. However, nectar alkaloids did not affect female plant reproduction, measured as pollen receipt, fruit set, seed set, and seed mass. The weak effects of nectar alkaloids on female reproduction could represent a balance between the altered behavior of nectar robbers and pollinators, or it could be that neither of these interactions affected plant reproduction. Taken together, these results suggest that secondary compounds in nectar may have more costs than benefits for plants.

The ecological significance of toxic nectar

Although plant‐herbivore and plant‐pollinator interactions have traditionally been studied separately, many traits are simultaneously under selection by both herbivores and pollinators. For example, secondary compounds commonly associated with herbivore defense have been found in the nectar of many plant species, and many plants produce nectar that is toxic or repellent to some floral visitors. Although secondary compounds in nectar and toxic nectar are geographically and phylogenetically widespread, their ecological significance is poorly understood. Several hypotheses have been proposed for the possible functions of toxic nectar, including encouraging specialist pollinators, deterring nectar robbers, preventing microbial degradation of nectar, and altering pollinator behavior. All of these hypotheses rest on the assumption that the benefits of toxic nectar must outweigh possible costs; however, to date no study has demonstrated that toxic nectar provides fitness benefits for any plant. Therefore, in addition to these adaptive hypotheses, we should also consider the hypothesis that toxic nectar provides no benefits or is tolerably detrimental to plants, and occurs due to previous selection pressures or pleiotropic constraints. For example, secondary compounds may be transported into nectar as a consequence of their presence in phloem, rather than due to direct selection for toxic nectar. Experimental approaches are necessary to understand the role of toxic nectar in plant‐animal interactions.

Feeding responses by female Pieris brassicae butterflies to carbohydrates and amino acids

SummaryMost Lepidoptera feed during the adult stage on carbohydrate‐rich food sources, primarily floral nectar. However, little is known about the factors leading to the acceptance of a possible food source. It is reported that butterflies select for nectar rich in sucrose and amino acids. This suggests that the insects have developed a sensitivity to these nectar compounds. We tested females of the large cabbage white, Pieris brassicae L. (Lepidoptera: Pieridae) for their responses to 10 different nectar‐ or honeydew‐sugars after either tarsal or proboscis stimulation. In no‐choice experiments, food‐deprived P. brassicae showed the strongest response to sucrose, followed by fructose. Other sugars, including galactose, glucose, maltose, mannose, melezitose, melibiose, raffinose and trehalose, did not elicit a feeding response. Mixtures of essential or common non‐essential amino acids did not stimulate feeding. In a choice situation, P. brassicae preferred sucrose over fructose, whereas they accepted a sucrose and amino acid solution equally to a plain sucrose solution. The results indicate that for P. brassicae, feeding is mainly elicited by sucrose and fructose.

Ants Like Flower Nectar

Ants Like Flower Nectar