ORCHID BEES DON'T NEED ORCHIDS: EVIDENCE FROM THE NATURALIZATION OF AN ORCHID BEE IN FLORIDA

Plant Resource Use and Pattern of Usage by the Naturalized Orchid Bee (Euglossa dilemma: Hymenoptera: Apidae) in Florida

The Neotropical orchid bee Euglossa dilemma was found to be naturalized in southern Florida in 2003, and, by 2022, it had colonized the southern half of Florida. Observations of the bee's collection of plant resources, primarily flowers, were made from 2003 through to 2022 to document its plant usage and understand the patterns of its plant usage. The bee utilized 259 plant taxa, 237 species, and 22 horticultural forms, in 156 genera and 56 families in 263 total uses. Of 247 taxa of flowers, 120 were visited primarily for nectar, 46 for both nectar and pollen, 60 for pollen, including 42 buzz-pollinated flowers, 15 for fragrance chemicals for the males, and 5 for resin rewards by females for nesting. Fragrance chemicals were also collected by males from the leaves of 12 plant species. These extensive resource use data allowed the following predictions to be made. (1) The bee's presence in Florida, distant from its native region of Mexico and Central America and the geographical ranges of other orchid bees, would result the usage of many new taxa of plants. True, half, 74/148 (50%), of the genera and one third, 16/51(31%), of the plant families of the plants with flowers used by the bee were not previously recorded as being utilized by Euglossine bees. (2) Like other naturalized bees, it would use relatively more plants from its native range or congeners of these plants. True, 113/148 (76%) of genera with species bearing collected floral rewards are native or congeners with species native to the bee's native range. (3) Given the bee's long tongue, ability to buzz pollen from poricidal anthers, and ability to collect and use specialized rewards, it would disproportionately use plants with protected or highly specialized floral rewards. True, 180/247 (72%) utilized species bear rewards which were protected and unavailable to, or of no interest to, most other flower visitors.

The Nighttime Fragrance of Guettarda scabra (Rubiaceae): Flower Scent and Its Implications for Moth Pollination

Floral scent is crucial for attracting pollinators, especially in plants that bloom at night. However, chemical profiles of flowers from nocturnal plants with varied floral morphs are poorly documented, limiting our understanding of their pollination ecology. We investigated the floral scent in Guettarda scabra (L.) Vent. (Rubiaceae), a night-blooming species with short- and long-styled floral morphs, found in the threatened pine rocklands in south Florida, US. By using dynamic headspace sampling and GC-MS analysis, we characterized the chemical profiles of the floral scent in both morphs. Neutral red staining was also employed to determine the specific floral regions responsible for scent emission in G. scabra. The results revealed that G. scabra's fragrance consists entirely of benzenoid and terpenoid compounds, with benzeneacetaldehyde and (E)-β-ocimene as dominant components. There were no differences in the chemical profiles between the long- and short-styled flowers. Staining assays indicated that the corolla lobes, anthers, and stigma were the primary sources of the scent. These findings indicate that G. scabra's floral scent is consistent with that of night-blooming plants pollinated by nocturnal hawkmoths, providing important insights into its chemical ecology and pollinator attraction. This study demonstrates how floral scent chemistry can validate predictions based on flower morphology in hawkmoth-pollinated plants.

Seasonal stability and species specificity of environmentally acquired chemical mating signals in orchid bees

Traits that mediate reproductive isolation between species, such as those involved in mate choice and/or recognition, are predicted to experience stabilizing selection towards the species mean. Male orchid bees collect chemical compounds from many sources, such as plants and fungi, which they use as a perfume signal (pheromone) during courtship display, and are suggested to contribute to reproductive isolation between species. Environmentally acquired signals are more prone to variation as source availability can vary through space and time. If orchid bee perfumes are important for reproductive isolation between species, we expect them to exhibit stable species-specific differences in time and space. Here, we describe phenotypic patterns of inter- and intraspecific variation in the male perfumes of three sympatric species of Euglossa orchid bees across an entire year, investigating both their seasonality and species specificity. Our analysis revealed considerable within-species variation in perfumes. However, species specificity was maintained consistently throughout the year, supporting the idea that these perfumes could play an important role in reproductive isolation and are experiencing stabilizing selection towards a species mean. Our analysis also identified strong correlations in the abundance of some compounds, possibly due to shared collection sources between species. Our study suggests that orchid bee perfumes are robust in the face of environmental changes in resource availability and thus can maintain reproductive isolation between species.

More than Moths: Flower Visitors of a Night-Blooming Plant in South Florida Pine Rocklands, USA

Plants whose flowers open at night but remain open during the day also attract diurnal flower visitors, potentially boosting their pollination rates and providing resources that can support diverse arthropod communities. The rough-leaf velvetseed, Guettarda scabra (Rubiaceae), is an evergreen shrub that thrives only in the imperiled pine rockland habitat in south Florida. Its white, tubular, and fragrant flowers open during late afternoon, exhibiting traits strongly associated with the attraction of nocturnal hawkmoths (Sphingidae). Flowers of G. scabra remain open until the following morning, becoming available to a wider array of visitors, bringing into question the expectation that sphingophilous flowers are visited mainly by hawkmoths. To evaluate whether the flowers of G. scabra are mainly visited by nocturnal hawkmoths and understand the role of this plant in the pine rockland habitat, we characterized the arthropod fauna associated with its flowers during the morning, evening, and at night. We found that most flower visitors were diurnal insects of the orders Hymenoptera and Lepidoptera, although we observed other arthropod groups too. Visitation at night was dominated by two species of hawkmoths. Nectar was the main resource used by the arthropod community during this study. Legitimate visitation and nectar-robbing were the behaviors most frequently observed among the flower visitors. Our results suggest that flowers of the night-blooming G. scabra constitute an important food source for both diurnal and nocturnal arthropod fauna in the fire-dependent pine rocklands of southern Florida. Our study provides novel data to support efforts to conserve and protect pine rocklands and the plants and animals that inhabit them.

The Size of it: Scant Evidence That Flower Size Variation Affects Deception in Intersexual Floral Mimicry

Mutualisms involve cooperation, but also frequently involve conflict. Plant-pollinator mutualisms are no exception. To facilitate animal pollination, flowering plants often offer pollen (their male gametes) as a food reward. Since plants benefit by maximizing pollen export to conspecific flowers, we might expect plants to cheat on pollen rewards. In intersexual floral mimicry, rewarding pollen-bearing male flowers (models) are mimicked by rewardless female flowers (mimics) on the same plant. Pollinators should therefore learn to avoid the unrewarding mimics. Plants might impede such learning by producing phenotypically variable flowers that cause bees to generalize among models and mimics during learning. In this laboratory study, we used partially artificial flowers (artificial petals, live reproductive parts) modeled after Begonia odorata to test whether variation in the size of rewarding male flowers (models) and unrewarding female flowers (mimics) affected how quickly bees learned both to recognize models and to reject mimics. Live unrewarding female flowers have 33% longer petals and have 31% greater surface area than live rewarding male flowers, which bees should easily discriminate. Yet while bees rapidly learned to reduce foraging effort on mimics, learning was not significantly affected by the degree to which flower size varied. Additionally, we found scant evidence that this was a result of bees altering response speed to maintain decision accuracy. Our study failed to provide evidence that flower size variation in intersexual floral mimicry systems exploits pollinator cognition, though we cannot rule out that other floral traits that are variable may be important. Furthermore, we propose that contrary to expectation, phenotypic variability in a Batesian mimicry system may not necessarily have significant effects on whether receivers effectively learn to discriminate models and mimics.

Honey as a Functional Food for Apis mellifera

Although nectar is consumed, primarily as a supplemental food, by a broad range of insects spanning at least five orders, it is processed and stored by only a small number of species, most of which are bees and wasps in the superfamily Apoidea. Within this group, Apis mellifera has evolved remarkable adaptations facilitating nectar processing and storage; in doing so, this species utilizes the end product, honey, for diverse functions with few if any equivalents in other phytophagous insects. Honey and its phytochemical constituents, some of which likely derive from propolis, have functional significance in protecting honey bees against microbial pathogens, toxins, and cold stress, as well as in regulating development and adult longevity. The distinctive properties of A. mellifera honey appear to have arisen in multiple ways, including genome modification; partnerships with microbial symbionts; and evolution of specialized behaviors, including foraging for substances other than nectar. That honey making by A. mellifera involves incorporation of exogenous material other than nectar, as well as endogenous products such as antimicrobial peptides and royal jelly, suggests that regarding honey as little more than a source of carbohydrates for bees is a concept in need of revision.

Sensory bias and signal detection trade-offs maintain intersexual floral mimicry

Mimicry is common in interspecies interactions, yet conditions maintaining Batesian mimicry have been primarily tested in predator-prey interactions. In pollination mutualisms, floral mimetic signals thought to dupe animals into pollinating unrewarding flowers are widespread (greater than 32 plant families). Yet whether animals learn to both correctly identify floral models and reject floral mimics and whether these responses are frequency-dependent is not well understood. We tested how learning affected the effectiveness and frequency-dependence of imperfect Batesian mimicry among flowers using the generalist bumblebee, Bombus impatiens, visiting Begonia odorata, a plant species exhibiting intersexual floral mimicry. Unrewarding female flowers are mimics of pollen-rewarding male flowers (models), though mimicry to the human eye is imperfect. Flower-naive bees exhibited a perceptual bias for mimics over models, but rapidly learned to avoid mimics. Surprisingly, altering the frequency of models and mimics only marginally shaped responses by naive bees and by bees experienced with the distribution and frequency of models and mimics. Our results provide evidence both of exploitation by the plant of signal detection trade-offs in bees and of resistance by the bees, via learning, to this exploitation. Critically, we provide experimental evidence that imperfect Batesian mimicry can be adaptive and, in contrast with expectations of signal detection theory, functions largely independently of the model and mimic frequency. This article is part of the theme issue 'Signal detection theory in recognition systems: from evolving models to experimental tests'.

A missing piece in the puzzle: the presence of Euglossa viridissima in the Baja California Peninsula (Hymenoptera, Apidae)

Orchid bees are a conspicuous component of the neotropical bee fauna, with a few species reaching the northernmost natural distribution for the group in northwestern continental Mexico. Among them, Euglossa viridissima Friese is here reported for the first time in the Cape Region of the Baja California peninsula, Mexico, where no species of the group have been found previously. These records are presented, their biogeographical implications discussed, and some interpretations of the local factors that influence the bees is presented.

The Nuclear and Mitochondrial Genomes of the Facultatively Eusocial Orchid Bee Euglossa dilemma

Bees provide indispensable pollination services to both agricultural crops and wild plant populations, and several species of bees have become important models for the study of learning and memory, plant–insect interactions, and social behavior. Orchid bees (Apidae: Euglossini) are especially important to the fields of pollination ecology, evolution, and species conservation. Here we report the nuclear and mitochondrial genome sequences of the orchid bee Euglossa dilemma Bembé & Eltz. E. dilemma was selected because it is widely distributed, highly abundant, and it was recently naturalized in the southeastern United States. We provide a high-quality assembly of the 3.3 Gb genome, and an official gene set of 15,904 gene annotations. We find high conservation of gene synteny with the honey bee throughout 80 MY of divergence time. This genomic resource represents the first draft genome of the orchid bee genus Euglossa, and the first draft orchid bee mitochondrial genome, thus representing a valuable resource to the research community.

Positive and Negative Impacts of Non-Native Bee Species around the World

Though they are relatively understudied, non-native bees are ubiquitous and have enormous potential economic and environmental impacts. These impacts may be positive or negative, and are often unquantified. In this manuscript, I review literature on the known distribution and environmental and economic impacts of 80 species of introduced bees. The potential negative impacts of non-native bees include competition with native bees for nesting sites or floral resources, pollination of invasive weeds, co-invasion with pathogens and parasites, genetic introgression, damage to buildings, affecting the pollination of native plant species, and changing the structure of native pollination networks. The potential positive impacts of non-native bees include agricultural pollination, availability for scientific research, rescue of native species, and resilience to human-mediated disturbance and climate change. Most non-native bee species are accidentally introduced and nest in stems, twigs, and cavities in wood. In terms of number of species, the best represented families are Megachilidae and Apidae, and the best represented genus is Megachile. The best studied genera are Apis and Bombus, and most of the species in these genera were deliberately introduced for agricultural pollination. Thus, we know little about the majority of non-native bees, accidentally introduced or spreading beyond their native ranges.

Rapid evolution of chemosensory receptor genes in a pair of sibling species of orchid bees (Apidae: Euglossini)

Background

Insects rely more on chemical signals (semiochemicals) than on any other sensory modality to find, identify, and choose mates. In most insects, pheromone production is typically regulated through biosynthetic pathways, whereas pheromone sensory detection is controlled by the olfactory system. Orchid bees are exceptional in that their semiochemicals are not produced metabolically, but instead male bees collect odoriferous compounds (perfumes) from the environment and store them in specialized hind-leg pockets to subsequently expose during courtship display. Thus, the olfactory sensory system of orchid bees simultaneously controls male perfume traits (sender components) and female preferences (receiver components). This functional linkage increases the opportunities for parallel evolution of male traits and female preferences, particularly in response to genetic changes of chemosensory detection (e.g. Odorant Receptor genes). To identify whether shifts in pheromone composition among related lineages of orchid bees are associated with divergence in chemosensory genes of the olfactory periphery, we searched for patterns of divergent selection across the antennal transcriptomes of two recently diverged sibling species Euglossa dilemma and E. viridissima.

Results

We identified 3185 orthologous genes including 94 chemosensory loci from five different gene families (Odorant Receptors, Ionotropic Receptors, Gustatory Receptors, Odorant Binding Proteins, and Chemosensory Proteins). Our results revealed that orthologs with signatures of divergent selection between E. dilemma and E. viridissima were significantly enriched for chemosensory genes. Notably, elevated signals of divergent selection were almost exclusively observed among chemosensory receptors (i.e. Odorant Receptors).

Conclusions

Our results suggest that rapid changes in the chemosensory gene family occurred among closely related species of orchid bees. These findings are consistent with the hypothesis that strong divergent selection acting on chemosensory receptor genes plays an important role in the evolution and diversification of insect pheromone systems.

Electronic supplementary material

The online version of this article (doi:10.1186/s12862-015-0451-9) contains supplementary material, which is available to authorized users.

Acquisition of species-specific perfume blends: influence of habitat-dependent compound availability on odour choices of male orchid bees (Euglossa spp.)

Male orchid bees (Euglossini, Apidae, Hymenoptera) expose species-specific blends of volatile chemicals (perfume bouquets) during their courtship display. The perfumes are acquired by collecting fragrant substances from environmental sources, which are then accumulated in specialised hind leg pouches. To balance the perfume composition, the males need to find and collect the required substances in specific relative amounts while facing seasonal, local or habitat-dependent differences in compound availability. Experience-dependent choice of odours, i.e. 'learned avoidance' of recently collected components, has been proposed as the mechanism that mediates the accumulation of the stereotypical compound ratios. In the present study, we used the presence of certain compounds in male hind leg pouches as proxy for the respective local compound availability, and investigated whether differences in content are correlated with differences in chemical choice assays. Our results suggest that volatile availability differs between localities (n = 16) as well as habitats (n = 2; coastal vs. inland) across the Yucatán peninsula, Mexico, for both studied species. Male Euglossa dilemma showed a pronounced preference for benzyl benzoate and eugenol at locations where those compounds were rare in hind leg extracts, as predicted by the learned avoidance model. No equivalent correlations were found for Euglossa viridissima. This is the first study to combine chemical analyses of perfumes with bioassays of odour choice. It strengthens the view that negative feedback from collected odours modifies future chemical choice and helps males to acquire specific perfume blends.

Orchid bees (Hymenoptera: Apidae) in the coastal forests of southern Brazil: diversity, efficiency of sampling methods and comparison with other Atlantic forest surveys

Surveys of orchid bees at the Brazilian Atlantic forest have been restricted to a few regions, making difficult to understand latitudinal patterns of distribution and diversity of these bees. For this reason we sampled the euglossine fauna at Atlantic forest areas at the coastal region of São Paulo (Sete Barras, Faz. Morro do Capim: SP3) and state of Paraná (Antonina, Reserva Natural do Rio Cachoeira: PR3), in southern Brazil. In PR3, we also evaluated the efficiency of collecting methods for sampling the fauna, comparing bait traps with direct collecting using entomological nets on fragrance baits. The diversity and abundance of bees was very low: we caught only 39 males of eight species in SP3 (Euglossa iopoecila, Euglossa roderici, Eulaema nigrita, Euglossa annectans, Eulaema cingulata, Euglossa pleosticta, Euglossa viridis and Exaerete smaragdina) and 254 males of six species in PR3 (Euglossa iopoecila, Euglossa annectans, Euglossa stellfeldi, Euglossa roderici, Euglossa pleosticta and Eulaema nigrita). Comparing the sampling methodologies, use of insect nets on fragrance baits (six species; 221 specimens) was more efficient than bait traps (three species; 33 specimens). When comparing the faunas of these two areas with other surveys at the Atlantic forest sites, through a DCA analysis, we found that the two surveys presented in this paper were placed relatively close to each other, but apart from the other sites analyzed, not clustering with the southernmost survey at the subtropical Atlantic forest of Rio Grande do Sul or with the remaining surveys carried out at northern lowland sites of this biome.

Intraspecific geographic variation of fragrances acquired by orchid bees in native and introduced populations

Male orchid bees collect volatiles, from both floral and non-floral sources, that they expose as pheromone analogues (perfumes) during courtship display. The chemical profile of these perfumes, which includes terpenes and aromatic compounds, is both species-specific and divergent among closely related lineages. Thus, fragrance composition is thought to play an important role in prezygotic reproductive isolation in euglossine bees. However, because orchid bees acquire fragrances entirely from exogenous sources, the chemical composition of male perfumes is prone to variation due to environmental heterogeneity across habitats. We used Gas Chromatography/Mass Spectrometry (GC/MS) to characterize the perfumes of 114 individuals of the green orchid bee (Euglossa aff. viridissima) sampled from five native populations in Mesoamerica and two naturalized populations in the southeastern United States. We recorded a total of 292 fragrance compounds from hind-leg extracts, and found that overall perfume composition was different for each population. We detected a pronounced chemical dissimilarity between native (Mesoamerica) and naturalized (U.S.) populations that was driven both by proportional differences of common compounds as well as the presence of a few chemicals unique to each population group. Despite these differences, our data also revealed remarkable qualitative consistency in the presence of several major fragrance compounds across distant populations from dissimilar habitats. In addition, we demonstrate that naturalized bees are attracted to and collect large quantities of triclopyr 2-butoxyethyl ester, the active ingredient of several commercially available herbicides. By comparing incidence values and consistency indices across populations, we identify putative functional compounds that may play an important role in courtship signaling in this species of orchid bee.

Large-range movements of neotropical orchid bees observed via radio telemetry

Neotropical orchid bees (Euglossini) are often cited as classic examples of trapline-foragers with potentially extensive foraging ranges. If long-distance movements are habitual, rare plants in widely scattered locations may benefit from euglossine pollination services. Here we report the first successful use of micro radio telemetry to track the movement of an insect pollinator in a complex and forested environment. Our results indicate that individual male orchid bees (Exaerete frontalis) habitually use large rainforest areas (at least 42-115 ha) on a daily basis. Aerial telemetry located individuals up to 5 km away from their core areas, and bees were often stationary, for variable periods, between flights to successive localities. These data suggest a higher degree of site fidelity than what may be expected in a free living male bee, and has implications for our understanding of biological activity patterns and the evolution of forest pollinators.

An olfactory shift is associated with male perfume differentiation and species divergence in orchid bees

Saltational changes may underlie the diversification of pheromone communication systems in insects, which are normally under stabilizing selection favoring high specificity in signals and signal perception. In orchid bees (Euglossini), the production of male signals depends on the sense of smell: males collect complex blends of volatiles (perfumes) from their environment, which are later emitted as pheromone analogs at mating sites. We analyzed the behavioral and antennal response to perfume components in two male morphotypes of Euglossa cf. viridissima from Mexico, which differ in the number of mandibular teeth. Tridentate males collected 2-hydroxy-6-nona-1,3-dienyl-benzaldehyde (HNDB) as the dominant component of their perfume. In bidentate males, blends were broadly similar but lacked HNDB. Population genetic analysis revealed that tri- and bidentate males belong to two reproductively isolated lineages. Electroantennogram tests (EAG and GC-EAD) showed substantially lower antennal responses to HNDB in bidentate versus tridentate males, revealing for the first time a mechanism by which closely related species acquire different chemical compounds from their habitat. The component-specific differences in perfume perception and collection in males of two sibling species are in agreement with a saltational, olfaction-driven mode of signal perfume evolution. However, the response of females to the diverged signals remains unknown.

Perfume-collecting male euglossine bees as pollinators of a basal angiosperm: the case of Unonopsis stipitata (Annonaceae)

Pollination of Unonopsis stipitata (Annonaceae) by males of two perfume-collecting bees, Euglossa imperialis and Eulaema bombiformis (Euglossini) is described. This is the first detailed account of this pollination mode in a member of a basal angiosperm family. Pollinator behaviour, identification of the odour bouquet and electrophysiological reaction of one of the two pollinators to the odour bouquet were determined. The collected odour is produced by 'osmophores' located adaxially on the petals. Starch and polysaccharides accumulated in petals are metabolized during odour emission. Mainly monoterpenes were detected in the scent samples, among them trans-carvone oxide. This molecule is thought by several authors to be the key attractant for male Eulaema bees and may be pivotal for convergent evolution of the perfume-collecting syndrome among dicotyledonous and monocotyledonous plants. It is speculated that Unonopsis, which on the basis of molecular age dating is considered a relatively recent genus of the Annonaceae (being 15-30 million years old), has diversified in relation to male euglossine bee pollinators.

Solitary invasive orchid bee outperforms co-occurring native bees to promote fruit set of an invasive Solanum

Our understanding of the effects of introduced invasive pollinators on plants has been exclusively drawn from studies on introduced social bees. One might expect, however, that the impacts of introduced solitary bees, with much lower population densities and fewer foragers, would be small. Yet little is known about the potential effects of naturalized solitary bees on the environment. We took advantage of the recent naturalization of an orchid bee, Euglossa viridissima, in southern Florida to study the effects of this solitary bee on reproduction of Solanum torvum, an invasive shrub. Flowers of S. torvum require specialized buzz pollination. Through timed floral visitor watches and two pollination treatments (control and pollen supplementation) at three forest edge and three open area sites, we found that the fruit set of S. torvum was pollen limited at the open sites where the native bees dominate, but was not pollen limited at the forest sites where the invasive orchid bees dominate. The orchid bee's pollination efficiency was nearly double that of the native halictid bees, and was also slightly higher than that of the native carpenter bee. Experiments using small and large mesh cages (to deny or allow E. viridissima access, respectively) at one forest site indicated that when the orchid bee was excluded, the flowers set one-quarter as many fruit as when the bee was allowed access. The orchid bee was the most important pollinator of the weed at the forest sites, which could pose additional challenges to the management of this weed in the fragmented, endangered tropical hardwood forests in the region. This specialized invasive mutualism may promote populations of both the orchid bee and this noxious weed. Invasive solitary bees, particularly species that are specialized pollinators, appear to have more importance than has previously been recognized.

COLLAPSE OF A POLLINATION WEB IN SMALL CONSERVATION AREAS

A suspected global decline in pollinators has heightened interest in their ecological significance. In a worst-case scenario, the decline of generalist pollinators is predicted to trigger cascades of linked declines among the multiple specialist plant species to which they are linked, but this has not been documented. I studied a portion of a pollination web involving a generalist pollinator, the oil-collecting bee Rediviva peringueyi, and a community of oil-secreting plants. Across 27 established conservation areas located in the Cape Floral Region, I found substantial variation in the bees' occurrence in relation to soil type and the successional stage of the vegetation. Anthropogenic declines were detectable against this background of naturally occurring variation: R. peringueyi was absent from small conservation areas (< 385 ha) in an urban matrix. In the absence of the bee, seed set failed in six specialist plant species that are pollinated only by R. peringueyi but remained high in a pollination generalist, which had replacement pollinators. The findings are consistent with theoretical predictions of the importance of generalist pollinators in maintaining the structure of pollination webs.