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

The Effect of Biogenic Amines in the Neuromodulation of Insect Social Behavior

Interactions among colony members in insect societies involve a wide range of behaviors, including collective defense, recruitment, foraging, and parental care. Despite significant advances in research, our understanding of how variations in neuroanatomical structure and physiological conditions drive changes in behavior remains incomplete. This review examines the critical role of biogenic amines in modulating social behaviors in insects. We highlight recent findings that demonstrate how these molecular messengers interact with hormonal signaling pathways, affecting essential colony traits such as development, fertility, reproduction, and caste differentiation. Caste-specific adaptations are evident in the brains of eusocial species. Key insights suggest that the aminergic system is fundamental for the transition from solitary to social structures. Research on insect brain architecture indicates that social evolution has led to changes in neural circuits rather than simply an increase in brain size. Besides regulating intra-colony dynamics, biogenic amines significantly influence interactions between social insects and other species. These findings may challenge established notions of mutualism, such as pollination or other plant-insect interactions, suggesting that some behaviours could result from brain manipulation via aminergic control. We argue that understanding the complex interplay of various biogenic amines and other molecular messengers is essential for comprehending the neuroendocrine signaling mechanisms that underlie insect social structures. By synthesizing recent findings and examples, this review provides an overview of how biogenic amines contribute to the evolution of social behaviors in insects, offering insights for future research in this field.

Nectar metabolomes contribute to pollination syndromes

'Pollination syndromes', where convergent floral signals reflect selection from a functional pollinator group, are often characterized by physical features, yet floral rewards such as nectar may also reflect selection from pollinators. We asked whether nectar chemistry shows evidence of convergence across functional pollinator groups, i.e. a 'chemical pollination syndrome'. We used untargeted metabolomics to compare nectar and leaf chemical profiles across 19 bee- and bird-syndrome species, focusing on Salvia spp. (Lamiaceae), selected to maximize switching events between pollination syndromes. We found that independently derived bird-syndrome nectar showed convergence on nectar traits distinct from bee-syndrome nectar, primarily driven by the composition and concentration of alkaloid profiles. We did not find evidence for 'passive leaking' of nectar compounds from leaves since metabolite abundances were uncorrelated across tissues and many nectar metabolites were not present in leaves. Nectar and leaf metabolomes were strongly decoupled from phylogenetic relationships within Salvia. These results suggest that functional pollinator groups may drive the evolution of floral reward chemistry, consistent with our 'chemical pollination syndrome' hypothesis and indicative of selection by pollinators, but we also consider alternative explanations. In addition, our results support the notion that nectar chemistry can be decoupled from that of other tissues.

A guide to sunflowers: floral resource nutrition for bee health and key pollination syndromes

Sunflower, Helianthus annuus L., is a prominent global oilseed crop with rising cultivation and appeal as a bee-friendly plant by providing abundant floral resources for pollinators. Mass-flowering crops can increase the availability of resources, and sunflower is a good opportunity to relieve pollen scarcity during the late summer in agricultural landscapes. Yet this should be taken with caution as they also provide a homogeneous source of nutrition. This study aimed to review and summarize the nutritional profile of sunflower pollen, nectar, bee bread, and honey, while assessing their effects on bee survival, development, and health. Furthermore, we present here the general state of knowledge on additional pollinator syndromes that extend beyond floral resources, including those influencing pollinator visual and olfactory attraction. We found that while sunflower pollen's nutritional quality is questioned due to lower protein and amino acid deficiencies, its nutrient content, like nectar sugars, had large variability. Sunflower pollen consumption showed mixed effects on Apis mellifera and Bombus species, sometimes negatively impacting development and survival. However, studies have conveyed a positive impact on bee health as sunflower pollen consistently reduced the infection intensity of the gut parasite, Crithidia bombi, in Bombus species. This probes the question on defining the quality of floral resources, emphasizing the need for caution when categorizing sunflower as a low quality nutritional resource. This review also outlines the importance of sunflower nectar characteristics (sugar content and volume) and floral morphology (flower pigmentation and corolla length) on pollinator foraging preferences. A prominent knowledge gap persists regarding nectar chemistry and sunflowers' extensive volatile profile to better understand the pollination syndromes that drive its pollinator interactions.

Biogenic amines in honey bee cognition: neurochemical pathways and stress impacts

Honey bees, as indispensable pollinators, rely on sophisticated neuromodulatory networks to regulate learning, memory, and social behaviors, all essential for colony function, ecosystem stability, and global agricultural systems. Biogenic amines octopamine, dopamine, serotonin, and tyramine are key modulators of these cognitive and behavioral processes, regulating foraging efficiency, navigational precision, and division of labor. However, we argue that anthropogenic stressors, including pesticides, pollutants, heavy metals, and microbiome dysbiosis, disrupt aminergic pathways by impairing neurotransmitter synthesis and neuronal signaling, leading to maladaptive behaviors and colony collapse. Recent discoveries expand this paradigm, revealing those biogenic amines in floral nectar act as exogenous neurochemicals, potentially altering pollinator behavior; however, their interaction with agrochemicals remains underexplored. While most studies focus on Apis mellifera, we caution that cautious extrapolation to wild and solitary bees is critical, given the evolutionary conservation of aminergic signaling across insect taxa. Cognitive deficits observed in managed honeybees likely extend to wild pollinators, threatening pollination network resilience and food security. To address these gaps, we advocate for CRISPR-based neurogenetic tools and multi-omics approaches to dissect stress susceptibility and biogenic amine (BA) regulation. Integrating neurobiology, ecotoxicology, and conservation science is imperative to develop precision strategies that mitigate anthropogenic threats, safeguard biodiversity, and stabilize global agriculture.

Effects of heavy metals and metalloids on plant-animal interaction and biodiversity of terrestrial ecosystems-an overview

Heavy metals and metalloids are ubiquitous and persistent in the environment. Anthropogenic activities, including land use change, industrial emissions, mining, chrome plating, and smelting, escalate their distribution and accumulation in terrestrial ecosystems. Priority metals, including lead, chromium, arsenic, nickel, copper, cadmium, and mercury, pose enormous risks to public health, ecological safety, and biodiversity. The adverse effects of heavy metals on plant-animal interactions, pollen viability, species fitness, richness, and abundance are poorly understood. Hence, this review summarises the critical insights from primary investigations on the key sources of heavy metal pollution, distribution pathways, and their adverse effects on plants and pollinators. This study provides insights into how heavy metals compromise nectar quality, pollen viability, plant-pollinator growth, and reproduction. Biotic pollinators are responsible for approximately 90% of the reproduction of flowering plants. Heavy metals adversely affect pollinators that rely on angiosperms for nectar and pollen. Heavy metals interrupt pollinators' and plants' growth, reproduction, and survival. Evidence showed that bees near gold mines had their olfactory learning performances and head sizes reduced by 36% and 4% due to heavy metals exposure. Cadmium (Cd) interrupts the redox balance, causes oxidative stress, alters gut microbiota, and reduces the survival rate of Apis cerana cerana. Excess Cd exposure reduced the flight capacity, loss of mitochondria, and damaged muscle fibre of Bombus terrestris, while Zn stress reduced egg production and hatchability of Harmonia axyridis. Furthermore, heavy metals alter flower visitation, foraging behaviour, and pollination efficiency.

Pollinator cognition and the function of complex rewards

The cognitive ecology of pollination is most often studied using simple rewards, yet flowers often contain multiple types of chemically complex rewards, each varying along multiple dimensions of quality. In this review we highlight ways in which reward complexity can impact pollinator cognition, demonstrating the need to consider ecologically realistic rewards to fully understand plant-pollinator interactions. We show that pollinators' reward preferences can be modulated by reward chemistry and the collection of multiple reward types. We also discuss how reward complexity can mediate pollinator learning through a variety of mechanisms, both with and without reward preference being altered. Finally, we show how an understanding of decision-making strategies is necessary to predict how pollinators' evaluation of reward options depends on the other options available.

Acute exposure to caffeine improves foraging in an invasive ant

Argentine ants, Linepithema humile, are a particularly concerning invasive species. Control efforts often fall short likely due to a lack of sustained bait consumption. Using neuroactives, such as caffeine, to improve ant learning and navigation could increase recruitment and consumption of toxic baits. Here, we exposed L. humile to a range of caffeine concentrations and a complex ecologically relevant task: an open landscape foraging experiment. Without caffeine, we found no effect of consecutive foraging visits on the time the ants take to reach a reward, suggesting a failure to learn the reward's location. However, under low to intermediate caffeine concentrations ants were 38% faster with each consecutive visit, implying that caffeine boosts learning. Interestingly, such improvements were lost at high doses. In contrast, caffeine had no impact on the ants' homing behavior. Adding moderate levels of caffeine to baits could improve ant's ability to learn its location, improving bait efficacy.

Field agrochemical exposure impacts locomotor activity in wild bumblebees

Agricultural intensification has been identified as one of the key causes of global insect biodiversity losses. These losses have been further linked to the widespread use of agrochemicals associated with modern agricultural practices. Many of these chemicals are known to have negative sublethal effects on commercial pollinators, such as managed honeybees and bumblebees, but less is known about the impacts on wild bees. Laboratory-based studies with commercial pollinators have consistently shown that pesticide exposure can impact bee behavior, with cascading effects on foraging performance, reproductive success, and pollination services. However, these studies typically assess only one chemical, neglecting the complexity of real-world exposure to multiple agrochemicals and other stressors. In the summer of 2020, we collected wild-foraging workers of the common eastern bumblebee, Bombus impatiens, from five squash (Cucurbita) agricultural sites (organic and conventional farms), selected to represent a range of agrochemical, including neonicotinoid insecticide, use. For each bee, we measured two behaviors relevant to foraging success and previously shown to be impacted by pesticide exposure: sucrose responsiveness and locomotor activity. Following behavioral testing, we used liquid chromatography-tandem mass spectrometry (LC-MS/MS) chemical analysis to detect and quantify the presence of 92 agrochemicals in each bumblebee. Bees collected from our sites did not vary in pesticide exposure as expected. While we found a limited occurrence of neonicotinoids, two fungicides (azoxystrobin and difenoconazole) were detected at all sites, and the pesticide synergist piperonyl butoxide (PBO) was present in all 123 bees. We found that bumblebees that contained higher levels of PBO were less active, and this effect was stronger for larger bumblebee workers. While PBO is unlikely to be the direct cause of the reduction in bee activity, it could be an indicator of exposure to pyrethroids and/or other insecticides that we were unable to directly quantify, but which PBO is frequently tank-mixed with during pesticide applications on crops. We did not find a relationship between agrochemical exposure and bumblebee sucrose responsiveness. To our knowledge, this is the first evidence of a sublethal behavioral impact of agrochemical exposure on wild-foraging bees.

Invasive ant learning is not affected by seven potential neuroactive chemicals

Argentine ants Linepithema humile are one of the most damaging invasive alien species worldwide. Enhancing or disrupting cognitive abilities, such as learning, has the potential to improve management efforts, for example by increasing preference for a bait, or improving ants' ability to learn its characteristics or location. Nectar-feeding insects are often the victims of psychoactive manipulation, with plants lacing their nectar with secondary metabolites such as alkaloids and non-protein amino acids which often alter learning, foraging, or recruitment. However, the effect of neuroactive chemicals has seldomly been explored in ants. Here, we test the effects of seven potential neuroactive chemicals-two alkaloids: caffeine and nicotine; two biogenic amines: dopamine and octopamine, and three nonprotein amino acids: β-alanine, GABA and taurine-on the cognitive abilities of invasive L. humile using bifurcation mazes. Our results confirm that these ants are strong associative learners, requiring as little as one experience to develop an association. However, we show no short-term effect of any of the chemicals tested on spatial learning, and in addition no effect of caffeine on short-term olfactory learning. This lack of effect is surprising, given the extensive reports of the tested chemicals affecting learning and foraging in bees. This mismatch could be due to the heavy bias towards bees in the literature, a positive result publication bias, or differences in methodology.

Caffeine Consumption Helps Honey Bees Fight a Bacterial Pathogen

Caffeine has long been used as a stimulant by humans. Although this secondary metabolite is produced by some plants as a mechanism of defense against herbivores, beneficial or detrimental effects of such consumption are usually associated with dose. The Western honey bee, Apis mellifera, can also be exposed to caffeine when foraging at Coffea and Citrus plants, and low doses as are found in the nectar of these plants seem to boost memory learning and ameliorate parasite infection in bees. In this study, we investigated the effects of caffeine consumption on the gut microbiota of honey bees and on susceptibility to bacterial infection. We performed in vivo experiments in which honey bees, deprived of or colonized with their native microbiota, were exposed to nectar-relevant concentrations of caffeine for a week, then challenged with the bacterial pathogen Serratia marcescens. We found that caffeine consumption did not impact the gut microbiota or survival rates of honey bees. Moreover, microbiota-colonized bees exposed to caffeine were more resistant to infection and exhibited increased survival rates compared to microbiota-colonized or microbiota-deprived bees only exposed to the pathogen. Our findings point to an additional benefit of caffeine consumption in honey bee health by protecting against bacterial infections. IMPORTANCE The consumption of caffeine is a remarkable feature of the human diet. Common drinks, such as coffee and tea, contain caffeine as a stimulant. Interestingly, honey bees also seem to like caffeine. They are usually attracted to the low concentrations of caffeine found in nectar and pollen of Coffea plants, and consumption improves learning and memory retention, as well as protects against viruses and fungal parasites. In this study, we expanded these findings by demonstrating that caffeine can improve survival rates of honey bees infected with Serratia marcescens, a bacterial pathogen known to cause sepsis in animals. However, this beneficial effect was only observed when bees were colonized with their native gut microbiota, and caffeine seemed not to directly affect the gut microbiota or survival rates of bees. Our findings suggest a potential synergism between caffeine and gut microbial communities in protection against bacterial pathogens.

To each their own! Nectar plasticity within a flower mediates distinct ecological interactions

Nuptial and extranuptial nectaries are involved in interactions with different animal functional groups. Nectar traits involved in pollination mutualisms are well known. However, we know little about those traits involved in other mutualisms, such as ant-plant interactions, especially when both types of nectaries are in the same plant organ, the flower. Here we investigated if when two types of nectaries are exploited by distinct functional groups of floral visitors, even being within the same plant organ, the nectar secreted presents distinct features that fit animal requirements. We compared nectar secretion dynamics, floral visitors and nectar chemical composition of both nuptial and extranuptial nectaries in natural populations of the liana Amphilophium mansoanum (Bignoniaceae). For that we characterized nectar sugar, amino acid and specialized metabolite composition by high-performance liquid chromatography. Nuptial nectaries were visited by three medium- and large-sized bee species and extranuptial nectaries were visited mainly by ants, but also by cockroaches, wasps and flies. Nuptial and extranuptial nectar differed regarding volume, concentration, milligrams of sugars per flower and secretion dynamics. Nuptial nectar was sucrose-dominated, with high amounts of γ-aminobutyric acid and β-aminobutyric acid and with theophylline-like alkaloid, which were all exclusive of nuptial nectar. Whereas extranuptial nectar was hexose-rich, had a richer and less variable amino acid chemical profile, with high amounts of serine and alanine amino acids and with higher amounts of the specialized metabolite tyramine. The nectar traits from nuptial and extranuptial nectaries differ in energy amount and nutritional value, as well as in neuroactive specialized metabolites. These differences seem to match floral visitors' requirements, since they exclusively consume one of the two nectar types and may be exerting selective pressures on the composition of the respective resources of interest.

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.