Artificial Nectar Research Articles

Wild bumblebees use both absolute and relative evaluation when foraging

Abstract Foraging theory assumes that animals assess value based on objective payoffs; however, animals often evaluate rewards comparatively, forming expectations based on recent experience. This form of evaluation may be particularly relevant for nectar foragers such as bumblebees, where individuals can visit thousands of flowers daily that vary in nectar quality. While many animals, including bees, demonstrate reference-based evaluation in experimental contexts, it is unclear whether this occurs in the wild. Here, we asked how daily experience with wildflower nectar influenced wild bumblebees’ reward evaluation. We measured the daily nectar concentration of bee-visited wildflowers (Penstemon spp.), before presenting foragers with conspecific flowers filled with a range of artificial nectar concentrations. We recorded bees’ acceptance of artificial nectar, the probability of subsequent visits to flowers on the same plant, and residence time. While bees had a minimum threshold of nectar acceptability that was unaffected by experience, when there was higher-concentration environmental nectar, they were less likely to accept lower-quality rewards on manipulated plants. Bees also visited more flowers and stayed longer on plants with higher-concentration nectar. This study shows evidence for both absolute and reference-based evaluation in wild bees and points towards differences between bees’ behavior in lab- and wild-foraging contexts.

Impacts of neonicotinoid insecticides on bumble bee energy metabolism are revealed under nectar starvation

Bumble bees are an important group of insects that provide essential pollination services as a consequence of their foraging behaviors. These pollination services are driven, in part, by energetic exchanges between flowering plants and individual bees. Thus, it is important to examine bumble bee energy metabolism and explore how it might be influenced by external stressors contributing to declines in global pollinator populations. Two stressors that are commonly encountered by bees are insecticides, such as the neonicotinoids, and nutritional stress, resulting from deficits in pollen and nectar availability. Our study uses a metabolomic approach to examine the effects of neonicotinoid insecticide exposure on bumble bee metabolism, both alone and in combination with nutritional stress. We hypothesized that exposure to imidacloprid disrupts bumble bee energy metabolism, leading to changes in key metabolites involved in central carbon metabolism. We tested this by exposing Bombus impatiens workers to imidacloprid according to one of three exposure paradigms designed to explore how chronic versus more acute (early or late) imidacloprid exposure influences energy metabolite levels, then also subjecting them to artificial nectar starvation. The strongest effects of imidacloprid were observed when bees also experienced nectar starvation, suggesting a combinatorial effect of neonicotinoids and nutritional stress on bumble bee energy metabolism. Overall, this study provides important insights into the mechanisms underlying the impact of neonicotinoid insecticides on pollinators, and underscores the need for further investigation into the complex interactions between environmental stressors and energy metabolism.

Blueberry floral probiotics: nectar microbes inhibit the growth of Colletotrichum pathogens.

To identify whether microorganisms isolated from blueberry flowers can inhibit the growth of Colletotrichum, an opportunistic plant pathogen that infects flowers and threatens yields, and to assess the impacts of floral microbes and Colletotrichum pathogens on artificial nectar sugars and honey bee consumption. The growth inhibition of Colletotrichum (Colletotrichum acutatum, Colletotrichum fioriniae, and Colletotrichum gloeosporioides) was screened using both artificial nectar co-culture and dual culture plate assays. All candidate nectar microbes were screened for antagonism against a single C. acutatum isolate. Then, the top four candidate nectar microbes showing the strongest inhibition of C. acutatum (Neokomagataea thailandica, Neokomagataea tanensis, Metschnikowia rancensis, and Symmetrospora symmetrica) were evaluated for antagonism against three additional C. acutatum isolates, and single isolates of both C. fioriniae and C. gloeosporioides. In artificial nectar assays, single and three-species cultures inhibited the growth of two of four C. acutatum isolates by ca. 60%, but growth of other Colletotrichum species was not affected. In dual culture plate assays, inhibition was observed for all Colletotrichum species for at least three of four selected microbial antagonists (13%‒53%). Neither honey bee consumption of nectar nor nectar sugar concentrations were affected by any microbe or pathogen tested. Selected floral microbes inhibited growth of all Colletotrichum species in vitro, although the degree of inhibition was specific to the assay and pathogen examined. In all microbial treatments, nectar sugars were preserved, and honey bee preference was not affected.

Sublethal effects of four insecticides targeting cholinergic neurons on partner and host finding in the parasitic wasp Nasonia vitripennis.

Lethal and sublethal effects of pesticides on non-target organisms are one of the causes of the current decline of many insect species. However, research in the past decades has focused primarily on pollinators, although other beneficial non-target organisms such as parasitic wasps may also be affected. We studied the sublethal effects of the four insecticides acetamiprid, dimethoate, flupyradifurone, and sulfoxaflor on pheromone-mediated sexual communication and olfactory host finding of the parasitic wasp Nasonia vitripennis. All agents target cholinergic neurons, which are involved in the processing of chemical information by insects. We applied insecticide doses topically and tested the response of treated wasps to sex pheromones and host-associated chemical cues. Additionally, we investigated the mating rate of insecticide-treated wasps. The pheromone response of females surviving insecticide treatment was disrupted by acetamiprid (≥0.63 ng), dimethoate (≥0.105 ng) and flupyradifurone (≥21ng), while sulfoxaflor had no significant effects at the tested doses. Olfactory host finding was affected by all insecticides (acetamiprid: ≥1.05 ng, dimethoate: ≥0.105 ng, flupyradifurone: ≥5.25 ng, sulfoxaflor: ≥0.52 ng). Remarkably, females treated with ≥0.21 ng dimethoate even avoided host odor. The mating rate of treated N. vitripennis couples was decreased by acetamiprid (6.3 ng), flupyradifurone (≥2.63 ng) and sulfoxaflor (2.63 ng) while dimethoate showed only minor effects. Finally, we determined the amount of artificial nectar consumed by N. vitripennis females within 48 hours. Considering this amount (approximately 2 µl) and the maximum concentrations of the insecticides reported in nectar, tested doses can be considered field realistic. Our results suggest that exposure of parasitic wasps to field-realistic doses of insecticides targeting the cholinergic system reduces their effectiveness as natural enemies by impairing the olfactory sense.

Floral nectar production: what cost to a plant?

Floral nectar production is central to plant pollination, and hence to human wellbeing. As floral nectar is essentially a solution in water of various sugars, it is likely a valuable plant resource, especially in terms of energy, with plants experiencing costs/trade-offs associated with its production or absorption and adopting mechanisms to regulate nectar in flowers. Possible costs of nectar production may also influence the evolution of nectar volume, concentration and composition, of pollination syndromes involving floral nectar, and the production of some crops. There has been frequent agreement that costs of floral nectar production are significant, but relevant evidence is scant and difficult to interpret. Convincing direct evidence comes from experimental studies that relate either enhanced nectar sugar production (through repeated nectar removal) to reduced ability to produce seeds, or increased sugar availability (through absorption of additional artificial nectar) to increased seed production. Proportions of available photosynthate allocated by plants to nectar production may also indicate nectar cost. However, such studies are rare, some do not include treatments of all (or almost all) flowers per plant, and all lack quantitative cost-benefit comparisons for nectar production. Additional circumstantial evidence of nectar cost is difficult to interpret and largely equivocal. Future research should repeat direct experimental approaches that relate reduced or enhanced nectar sugar availability for a plant with consequent ability to produce seeds. To avoid confounding effects of inter-flower resource transfer, each plant should experience a single treatment, with treatment of all or almost all flowers per plant. Resource allocation by plants, pathways used for resource transfer, and the locations of resource sources and sinks should also be investigated. Future research should also consider extension of nectar cost into other areas of biology. For example, evolutionary models of nectar production are rare but should be possible if plant fitness gains and costs associated with nectar production are expressed in the same currency, such as energy. It should then be possible to understand observed nectar production for different plant species and pollination syndromes involving floral nectar. In addition, potential economic benefits should be possible to assess if relationships between nectar production and crop value are evaluated.

Hummingbird ingestion of low-concentration ethanol within artificial nectar.

Both frugivores and nectarivores are potentially exposed to dietary ethanol produced by fermentative yeasts which metabolize sugars. Some nectarivorous mammals exhibit a preference for low-concentration ethanol solutions compared to controls of comparable caloric content, but behavioural responses to ethanol by nectar-feeding birds are unknown. We investigated dietary preference by Anna's Hummingbirds (Calypte anna) for ethanol-enhanced sucrose solutions. Via repeated binary-choice experiments, three adult male hummingbirds were exposed to sucrose solutions containing 0%, 1% or 2% ethanol; rates of volitional nectar consumption were measured over a 3 h interval. Hummingbirds did not discriminate between 0% and 1% ethanol solutions, but exhibited significantly reduced rates of consumption of a 2% ethanol solution. Opportunistic measurements of ethanol concentrations within hummingbird feeders registered values peaking at about 0.05%. Ethanol at low concentrations (i.e. up to 1%) is not aversive to Anna's Hummingbirds and may be characteristic of both natural and anthropogenic nectars upon which they feed. Given high daily amounts of nectar consumption by hummingbirds, chronic physiological exposure to ethanol can thus be substantial, although naturally occurring concentrations within floral nectar are unknown.

Adult monarch butterflies show high tolerance to neonicotinoid insecticides

Abstract Numerous studies have documented the negative effects of neonicotinoids on bees; it remains crucial to examine how neonicotinoids affect other non‐target nectar‐feeding insects, such as the monarch butterfly, Danaus plexippus. Wildflowers growing near agricultural areas can be contaminated with neonicotinoids that affect survival or cause sublethal changes to behaviours of nectar‐feeding insects. Nectar residues of imidacloprid and clothianidin found in milkweeds and wildflowers adjacent to agricultural field range from 0 to 72.8 ng/mL. At field‐relevant doses, two neonicotinoids (imidacloprid and clothianidin) were studied for their effects on adult monarch survival, reproduction, flight and behaviour. First, we fed adult monarchs artificial nectar solutions ranging from 15 to 386 ng/mL of imidacloprid and 19 to 531 ng/mL of clothianidin. Neonicotinoid ingestion slightly reduced monarch reproduction but had no significant effects on survival, weight change, or activity levels. Second, we fed monarchs higher clothianidin doses (909 and 4030 ng/mL), that exceed field‐relevant levels by 22 and 99 times. These higher doses reduced monarch nectar consumption, survival, flight performance and reaction time in response to a drop test. Results show that adult monarchs tolerate field‐relevant doses as high as 54 ng/mL for imidacloprid and 75 ng/mL for clothianidin, with minimal lethal or sub‐lethal effects until much higher doses are supplied. We conclude that adult monarchs are more tolerant of ingested clothianidin and imidacloprid than indicated by previous research.

Predatory Abilities of Two Mediterranean Ants on the Eggs and Larvae of the Codling Moth Cydia pomonella

The predatory ability of ants (Hymenoptera, Formicidae) against insect pests can offer an important service to agricultural activities and may sometimes be directly exploited in biological control strategies. The codling moth Cydia pomonella (Lepidoptera, Tortricidae) is a major agricultural pest of fruit orchards, whose biological control is complicated by the fact that the larvae spend most of their life protected within the fruits they damage. In a recent experiment in Europe, pear trees in which ant activity was artificially increased by the addition of sugary liquid dispensers (artificial nectaries) suffered less damage caused by the larvae to their fruits. While some ants were already known to prey upon the mature larvae or pupae of C. pomonella in the soil, prevention of fruit damage would require predation upon eggs or newly hatched larvae, which have not yet excavated into the fruits. We verified whether two different Mediterranean ants frequently observed in fruit orchards, Crematogaster scutellaris and Tapinoma magnum, were able to prey upon C. pomonella eggs and larvae in laboratory conditions. Our experiments demonstrated that both species similarly attacked and killed young C. pomonella larvae. On the other hand, the eggs mostly attracted the attention of T. magnum but were never damaged. Further field assessments are required to understand whether ants may also interfere with oviposition by adults or whether larger ant species, although generally rarer in orchards, may also prey upon eggs.

Plants with extrafloral nectaries share indirect defenses and shape the local arboreal ant community.

Associational resistance (AR) is a positive interaction in which a plant suffers less herbivoredamage due to its association with a protective plant. Here, we evaluated whether plants with extra-floral nectaries (EFNs) can share indirect defenses with neighboring plants. We sampled 45 individuals of an EFN-bearing liana (Smilax polyantha) and recorded whether their support species had EFNs. In S. polyantha, we measured foliar herbivory and flower and fruit production. We examined the ant species composition and visitation of S. polyantha and whether they changed according to the supporting plant type (with or without EFNs). We experimentally determined whether S. polyantha supplemented with artificial nectaries could share indirect defenses with defenseless neighboring plants. Support plants with EFNs indirectly benefited S. polyantha by sharing mutualistic ant species. Smilax polyantha supported by plants with EFNs had a more specific ant species composition, a higher number of visiting ants and ant species richness, and exhibitednearly 3 times less foliar herbivory. However, we did not observe differences in fruit production between the two groups of S. polyantha. Finally, we observed that S. polyantha with artificial nectaries increased ant visitation on neighboring plants 2.5 times. We provide evidence that interspecific neighbors with EFNs can experience reciprocal benefits by sharing indirect defenses. Such local effects might escalate and affect the structure of plant communities.

Continuous exchange of nectar nutrients in an Oriental hornet colony

Nutritional exchanges play a fundamental role in the evolution of animal societies. In higher animal societies, while adult individuals can be both food donors and receivers, the offspring usually only receive food from the adults. Hornets and wasps are fierce insect hunters that feed their larvae with prey. However, although the adults also consume floral nectar, the role of nectar in vespid nutrition has remained largely unknown. We provided experimental colonies of the Oriental hornet with artificial nectar enriched with a 13C-labeled amino acid, and found that a continuous cycle of nutrition took place, in which nectar nutrients were used and exchanged back and forth between adults and larvae. We posit that this continuous cycle of nutrients constitutes a mechanism contributing to social cohesion. In an additional experiment, we found that nectar consumption was essential for adult and larval survival, suggesting the importance of wasps and hornets as pollinators in natural ecosystems.

A Decrease in the Staminode-Mediated Visitor Screening Mechanism in Response to Nectar Robbers Positively Affects Reproduction in Delphinium caeruleum Jacq. ex Camb. (Ranunculaceae).

Simple SummaryNectar robbers frequently have direct or indirect negative effects on plant reproductive success. However, nectar robbers can also indirectly contribute to the reproductive success of plants in some cases. The negative effects of nectar robbing on plant reproductive success have been widely reported, but the reasons for possible positive effects demand further investigation. Hence, our study was designed to assess the effects of nectar robbers on the reproductive success of Delphinium caeruleum. This will facilitate an understanding of the mutualism between plants and their visitors.Nectar-robbing insects, which are frequently described as cheaters in plant–pollinator mutualisms, may affect plant reproductive fitness by obtaining nectar rewards without providing pollination services. The negative effects of nectar robbing on plant reproductive success have been widely reported, but the reasons for possible positive effects demand further investigation. The goal of the study was to evaluate the effects of nectar robbing on the reproductive success of Delphinium caeruleum. Two staminodes cover the stamens and pistils in the flowers of D. caeruleum, forming a “double door” type of structure that compels pollinators to physically manipulate the staminodes to access the sex organs. In order to explore whether the operative strength required to open the staminodes is affected by actions associated with nectar robbing, we set up five different treatment groups: no nectar robbing, natural nectar robbing, artificial nectar robbing, hole making, and nectar removal. A biological tension sensor was used to measure the operative strength required to open the staminodes in the flowers. We also assessed the effect of nectar robbing on the flower-visiting behavior of pollinators and the effect of nectar robbing on reproductive fitness by the flower. The results showed that the operative strength needed to open staminodes was reduced by nectar robbers but not by artificial nectar robbing, hole making, or nectar removal. The flowers’ continuous visitation rate and visitation frequency by pollinators decreased significantly in robbed flowers. Both the pollen export and pollen deposition in naturally robbed flowers were significantly higher than those in nonrobbed flowers. Our results demonstrate that nectar robbers play an indirect positive role in the reproductive fitness of D. caeruleum flowers by reducing the operative strength of staminodes to promote pollen transfer. The reduction in operative strength of staminodes might be an adaptive mechanism that responds to nectar robbing.

Nectar Source and Pollinator Cross Contamination and Persistence of Pyriproxyfen Associated with the Use of Autodissemination Techniques for Mosquito Control.

Controlling container inhabiting mosquitoes such as Aedes aegypti and Ae. albopictus is often difficult because of the requirement to treat small and inaccessible cryptic sources of water where larvae are located. Autodissemination approaches based on the dissemination of insect growth regulators (IGRs) have been demonstrated as an effective means to treat these cryptic larval habitats and provide population control. Autodissemination approaches are attractive because they are based on the mosquitoes disseminating small amounts of IGRs compared to more traditional insecticide applications. While dissemination of small amounts of IGRs seems like an advantage, these approaches could lead to unintended transfer and effects on nontarget insect pollinators by delivering highly potent IGRs to nectar sources. Here we looked for the indirect and direct transfer of pyriproxyfen (PPF) to natural and artificial nectar sources and painted lady butterflies, Vanessa cardui, in semifield cages using the release of treated Ae. albopictus males or an autodissemination station. We also performed persistence tests of PPF in oviposition containers and natural and artificial nectar sources when exposed to laboratory and natural conditions. The data suggest that there is direct and indirect transfer to nectar sources and V. cardui associated with the use of autodissemination approaches. We discuss the results in the context of using autodissemination approaches for mosquito control and the potential risks these approaches may pose to nontarget insect pollinators.

Indirect transfer of pyriproxyfen to European honeybees via an autodissemination approach.

The frequency of arboviral disease epidemics is increasing and vector control remains the primary mechanism to limit arboviral transmission. Container inhabiting mosquitoes such as Aedes albopictus and Aedes aegypti are the primary vectors of dengue, chikungunya, and Zika viruses. Current vector control methods for these species are often ineffective, suggesting the need for novel control approaches. A proposed novel approach is autodissemination of insect growth regulators (IGRs). The advantage of autodissemination approaches is small amounts of active ingredients compared to traditional insecticide applications are used to impact mosquito populations. While the direct targeting of cryptic locations via autodissemination seems like a significant advantage over large scale applications of insecticides, this approach could actually affect nontarget organisms by delivering these highly potent long lasting growth inhibitors such as pyriproxyfen (PPF) to the exact locations that other beneficial insects visit, such as a nectar source. Here we tested the hypothesis that PPF treated male Ae. albopictus will contaminate nectar sources, which results in the indirect transfer of PPF to European honey bees (Apis mellifera). We performed bioassays, fluorescent imaging, and mass spectrometry on insect and artificial nectar source materials to examine for intra- and interspecific transfer of PPF. Data suggests there is direct transfer of PPF from Ae. albopictus PPF treated males and indirect transfer of PPF to A. mellifera from artificial nectar sources. In addition, we show a reduction in fecundity in Ae. albopictus and Drosophila melanogaster when exposed to sublethal doses of PPF. The observed transfer of PPF to A. mellifera suggests the need for further investigation of autodissemination approaches in a more field like setting to examine for risks to insect pollinators.

Within‐Body Distributions and Feeding Effects of the Neonicotinoid Insecticide Clothianidin in Bumblebees (Bombus terrestris)

Bumblebees can be exposed to neonicotinoid pesticides through nectar and pollen collected from treated crops, which can cause lethal and sublethal effects in these nontarget pollinators. However, the body distribution of the compound after exposure to neonicotinoids in bumblebees is not well studied. Bumblebee colonies (Bombus terrestris, n = 20) were exposed to field-realistic concentrations of clothianidin through artificial nectar (3.6-13 µg/L) for 9 d. Comparison of the nominal with the measured exposure in nectar indicated good compliance, confirming the applicability of the method. When quantified, clothianidin showed a concentration-dependent occurrence in the head and body of workers (head: <0.2-2.17 µg/kg; body: <0.2-3.17 µg/kg), and in the body of queens (<0.2-2.49 µg/kg), although concentrations were below those measured in the nectar (bioaccumulation factor = 0.2). Exposure to clothianidin did not affect mortality nor brood production, nor did it have a statistically significant effect on nectar consumption and size of food storage. However, visual inspection suggests higher nectar consumption of nectar with low clothianidin content compared with nectar with no or high clothianidin content. Our results show that dietary clothianidin is taken up in bumblebees, but does not bioaccumulate to elevated levels compared with exposure. Still, clothianidin may elicit responses that affect feeding behavior of the pollinator B. terrestris, although our endpoints were not significantly affected. Environ Toxicol Chem 2021;40:2781-2790. © 2021 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Nectar provision attracts hummingbirds and connects interaction networks across habitats

Many ecosystems have been modified by humans, creating novel habitats that include human‐provided resources. Gardens adjacent to native habitats may affect plant–pollinator interactions by altering the determinants of interactions and species specialization. Here, we characterized a network comprising plants and hummingbirds interacting in a birdwatching garden with human‐provided resources (nectar feeders and exotic plants) and adjacent Andean cloud forest in Colombia. Specifically, we investigated the proportion of hummingbirds visiting feeders and native/exotic plants to evaluate the connection between the habitats and the ecological determinants of the interaction network. Hummingbirds relied heavily on artificial nectar feeders in the garden, leaving the natural cloud forest for resources. Morphological matching was the single most important predictor of the observed pairwise interactions, for both hummingbirds and plants. At the species level, longer flowering phenology and a higher amount of sugar in nectar led to a higher degree for plants (i.e. the number of visiting hummingbird species). In contrast, a longer floral corolla was associated with lower specialization. Abundance was the best predictor of the number of partners for hummingbirds. The garden created for birdwatching attracted most, but not all, hummingbird species beyond their natural cloud forest habitat. Interestingly, the most frequently visited plants in the garden were native, especially the endemic and endangered tree Zygia lehmannii (Fabaceae). Our results show that some ecological mechanisms determining interactions in natural communities still hold in intensively modified habitats. Furthermore, a compromise between conservation and hummingbirds’ attraction to birding lodges/gardens is possible, for instance by favouring native and endemic plant species that are highly attractive for pollinators.

Artificial nectar feeders reduce sunbird abundance and plant visitation in Cape Fynbos adjacent to suburban areas

Globally, people feed wild animals to interact with nature. Attracting nectarivorous birds to gardens using artificial nectar feeders is increasingly popular, yet little is known about its influence on birds and the plants they pollinate. We investigated effects of nectar feeders on African birds and their plant mutualists, by conducting feeding experiments in gardens and natural vegetation along the suburban edge of the Cape Peninsula, South Africa. We compared relative abundance and local distribution patterns of nectar-specialist, nectar-opportunist and non-nectarivore bird species between feeder and control treatments. We then tested whether nectar feeders in gardens affected visitation rates to two sunbird-pollinated Erica species in neighbouring vegetation compared to control sites. Nectar feeders increased the density of nectarivores (but not non-nectarivores) in gardens but decreased their density in neighbouring vegetation, even in winter when floral abundance was high. These changes in sunbird distribution patterns had no detectible influence on visitation rates to E. abietina, but decreased visitation to E. plukenetii flowers by on average 16% at least up to 300 m of gardens with feeders. Thus, although supplementary nectar feeding may have conservation value for nectarivorous birds by reducing their urban sensitivity, it can inadvertently interfere with bird-plant pollination networks by competing with native flowers for birds’ attention.

Nectar addition changes pollinator behavior but not plant reproduction in pollen-rewarding Lupinus argenteus.

In addition to its role as the male gamete, pollen is often used as a food reward for pollinators. Roughly 20,000 species of angiosperms are strictly pollen-rewarding, providing no other rewards to their pollinators. However, the influence of this strategy on pollinator behavior and plant reproduction is poorly understood, especially relative to the nectar-reward strategy. We performed a field experiment using the strictly pollen-rewarding Lupinus argenteus to explore how the absence of nectar influences pollinator behavior and plant reproduction. We added artificial nectar to Lupinus argenteus individuals to simulate a phenotype that would reward pollinators with both nectar and pollen. We compared bee pollinator behavior, via direct observation, and female reproduction between nectar-added and nectarless control plants. Bees exhibited behavioral responses to the novel reward, collecting nectar as well as pollen and spending 27% longer per flower. Pollen transfer increased with flower visit duration. However, plants in the study population were not pollen-limited; consequently, the observed changes in pollinator behavior did not result in changes in female components of plant reproduction. The addition of nectar to pollen-rewarding plants resulted in modest increases in per-flower pollinator visit duration and pollen transfer, but had no effect on reproduction because, at the place and time the experiment was conducted, plants were not pollen-limited. These results suggest that a pollen-only reward strategy may allow plants that are visited by pollen foragers to minimize some costs of reproduction by eliminating investment in other rewards, such as nectar, without compromising female plant fitness.

Reliability and quality of artificial nectar feeders for birds in the Cape Floristic Region

Supplementary feeding of birds may have considerable ecological and evolutionary effects on bird communities. However, there is a lack of basic information on the prevalence, frequency and quality of supplementary feeders, especially in African urban areas. Here we describe the prevalence, reliability and quality of artificial nectar feeders in suburbs in the Cape Floristic Region, South Africa, where many bird-pollinated plant species occur. Results from 291 questionnaires, completed by garden owners with an interest in birds, reveal that 57% of respondents have feeders in their gardens and 51% refill their feeders multiple times per week. The sugar concentration, total duration of feeding and frequency of feeding did not affect abundances or species richness of nectarivorous birds in gardens. We found a higher incidence of breeding sunbirds and sugarbirds in gardens with feeders than gardens without. Supplementary nectar feeding in this area has the potential to contribute to conserving nectarivorous birds, but investigation into the possible negative effects is needed.

The effect of toxic pyridine-alkaloid secondary metabolites on the sunbird gut microbiome

Sunbirds feed on tobacco tree nectar which contains toxic nicotine and anabasine secondary metabolites. Our aim was to understand the effect of nicotine and anabasine on the gut microbiota composition of sunbirds. Sixteen captive sunbirds were randomly assigned to two diets: artificial nectar either with (treatment) or without (control) added nicotine and anabasine. Excreta were collected at 0, 2, 4 and 7 weeks of treatment and samples were processed for bacterial culture and high-throughput amplicon sequencing of the 16S rRNA gene. The gut microbiome diversity of the treated and control birds changed differently along the seven-week experiment. While the diversity decreased in the control group along the first three samplings (0, 2 and 4 weeks), it increased in the treatment group. The microbiota composition analyses demonstrated that a diet with nicotine and anabasine, significantly changed the birds’ gut microbiota composition compared to the control birds. The abundance of nicotine- and anabasine- degrading bacteria in the excreta of the treated birds, was significantly higher after four and seven weeks compared to the control group. Furthermore, analysis of culturable isolates, including Lactococcus, showed that sunbirds’ gut-associated bacteria were capable of degrading nicotine and anabasine, consistent with their hypothesised role as detoxifying and nutritional symbionts.

I Can See You: Temporal Variation in Ant Aggressiveness Towards Herbivores under Continuous Provision of High- or Low-quality Food Sources

To reduce herbivory, plants bearing extrafloral nectaries interact with ants and attract them by providing food. As plant bodyguards, ants respond to the resource provision and, using their antennae, detect chemical messages from the host plants that help them to locate herbivores. Ants can also use their vision to explore the environment; however, information is lacking on how interactions between visual signs and the availability of extrafloral nectar affect ant aggressiveness near resources. We addressed the following question in this study: does the ants’ ability to visualize potential herbivores enhance their aggression under a constant provision of a high-quality food source? Using an experimental approach within the semiarid intertropical region of Tehuacan-Cuicatlán (Mexico), we manipulated the availability of food sources by constantly offering artificial nectaries on the shrub Prosopis laevigata (Fabaceae). Over two time periods (day and night), we tested how the presence of a high-quality food source affected ant aggressiveness to herbivores. Therefore, we offered dummy caterpillars and counted the number of marks left by enemy attacks. Overall the attack rate was extremely high: 84.25% of the dummy caterpillars were injured. Ants were responsible for 86.22% of the marks left by enemies, and their aggression increased during the day, especially towards caterpillars in trees with high-quality food sources. During the night, ants probably rely mostly on their antennae to detect potential herbivores; therefore, their ability to detect dummy caterpillars was greater during the day. We show that, besides nectar quality and availability, visualizing herbivores may enhance ant aggressiveness.