RESUMO
As pollen and nectar foragers, bees have long been considered strictly herbivorous. Their pollen provisions, however, are host to abundant microbial communities, which feed on the pollen before and/or while it is consumed by bee larvae. In the process, microbes convert pollen into a complex of plant and microbial components. Since microbes are analogous to metazoan consumers within trophic hierarchies, the pollen-eating microbes are, functionally, herbivores. When bee larvae consume a microbe-rich pollen complex, they ingest proteins from plant and microbial sources and thus should register as omnivores on the trophic "ladder." We tested this hypothesis by examining the isotopic compositions of amino acids extracted from native bees collected in North America over multiple years. We measured bee trophic position across the six major bee families. Our findings indicate that bee trophic identity was consistently and significantly higher than that of strict herbivores, providing the first evidence that omnivory is ubiquitous among bee fauna. Such omnivory suggests that pollen-borne microbes represent an important protein source for larval bees, which introduces new questions as to the link between floral fungicide residues and bee development.
Assuntos
Abelhas/fisiologia , Dieta , Microbiota , Aminoácidos/química , Fenômenos Fisiológicos da Nutrição Animal , Animais , Abelhas/crescimento & desenvolvimento , Isótopos/análise , Larva/crescimento & desenvolvimento , Larva/fisiologia , América do Norte , Pólen/microbiologiaRESUMO
Teeming within pollen provisions are diverse communities of symbiotic microbes, which provide a variety of benefits to bees. Microbes themselves may represent a major dietary resource for developing bee larvae. Despite their apparent importance in sustaining bee health, evidence linking pollen-borne microbes to larval health is currently lacking. We examined the effects of microbe-deficient diets on the fitness of larval mason bees. In a series of diet manipulations, microbe-rich maternally collected pollen provisions were replaced with increasing fractions of sterilized, microbe-deficient pollen provisions before being fed to developing larvae. Convergent findings from amino acid and fatty acid trophic biomarker analyses revealed that larvae derived a substantial amount of nutrition from microbial prey and occupied a significantly higher trophic position than that of strict herbivores. Larvae feeding on increasingly sterile diets experienced significant adverse effects on growth rates, biomass and survivorship. When completely deprived of pollen-borne microbes, larvae consistently exhibited marked decline in fitness. We conclude that microbes associated with aged pollen provisions are central to bee health, not only as nutritional mutualists, but also as a major dietary component. In an era of global bee decline, the conservation of such bee-microbe interactions may represent an important facet of pollinator protection strategies.
Assuntos
Abelhas/fisiologia , Larva/fisiologia , Valor Nutritivo , Pólen/microbiologia , Animais , Conservação dos Recursos Naturais , Cadeia Alimentar , Estimativa de Kaplan-MeierRESUMO
In most ecosystems, microbes are the dominant consumers, commandeering much of the heterotrophic biomass circulating through food webs. Characterizing functional diversity within the microbiome, therefore, is critical to understanding ecosystem functioning, particularly in an era of global biodiversity loss. Using isotopic fingerprinting, we investigated the trophic positions of a broad diversity of heterotrophic organisms. Specifically, we examined the naturally occurring stable isotopes of nitrogen ((15)N:(14)N) within amino acids extracted from proteobacteria, actinomycetes, ascomycetes, and basidiomycetes, as well as from vertebrate and invertebrate macrofauna (crustaceans, fish, insects, and mammals). Here, we report that patterns of intertrophic (15)N-discrimination were remarkably similar among bacteria, fungi, and animals, which permitted unambiguous measurement of consumer trophic position, independent of phylogeny or ecosystem type. The observed similarities among bacterial, fungal, and animal consumers suggest that within a trophic hierarchy, microbiota are equivalent to, and can be interdigitated with, macrobiota. To further test the universality of this finding, we examined Neotropical fungus gardens, communities in which bacteria, fungi, and animals are entwined in an ancient, quadripartite symbiosis. We reveal that this symbiosis is a discrete four-level food chain, wherein bacteria function as the apex carnivores, animals and fungi are meso-consumers, and the sole herbivores are fungi. Together, our findings demonstrate that bacteria, fungi, and animals can be integrated within a food chain, effectively uniting the macro- and microbiome in food web ecology and facilitating greater inclusion of the microbiome in studies of functional diversity.
Assuntos
Ecossistema , Microbiota , AnimaisRESUMO
Pheromone-based mating disruption has proven to be a powerful pest management tactic in many cropping systems. However, in the cranberry system, a viable mating disruption program does not yet exist. There are commercially available pheromones for several of the major pests of cranberries, including the cranberry fruitworm, Acrobasis vaccinii Riley (Lepidoptera: Pyralidae) and blackheaded fireworm, Rhopobota naevana (Hübner) (Lepidoptera: Tortricidae). Previous studies have shown that mating disruption represents a promising approach for R. naevana management although carrier and delivery technologies have remained unresolved. The present study examined the suitability of Specialized Pheromone & Lure Application Technology (SPLAT; ISCA Technologies, Inc., Riverside, CA), a proprietary wax and oil blend, to serve as a pheromone carrier in the cranberry system. In 2013 and 2014, we tested a blend of pheromones targeting A. vaccinii and R. naevana in field-scale, replicated trials. Pheromones were loaded into SPLAT and the resulting "SPLAT BFW CFW" formulation was deployed in commercial cranberry marshes. We compared moth trap-catch counts within SPLAT-treated blocks to those of conventionally managed blocks. In 2013, applications of SPLAT BFW CFW resulted in highly successful disruption of R. naevana and promising, though inconsistent, disruption of A. vaccinii. To improve disruption of A. vaccinii, the pheromone load was increased in 2014, providing 92% and 74% reductions in trap-catch for R. naevana and A. vaccinii, respectively. Importantly, larval infestation rates in SPLAT-treated blocks were lower than those of conventionally managed blocks. These results suggest that a multispecies mating disruption system (SPLAT BFW CFW) may represent an effective pesticide-alternative for serious pests of cranberries.
Assuntos
Mariposas/fisiologia , Controle Biológico de Vetores/métodos , Feromônios/farmacologia , Comportamento Sexual Animal/efeitos dos fármacos , Vaccinium macrocarpon , Animais , Especificidade da Espécie , Vaccinium macrocarpon/crescimento & desenvolvimento , WisconsinRESUMO
Arboreal herbivory is rare among mammals. The few species with this lifestyle possess unique adaptions to overcome size-related constraints on nutritional energetics. Sloths are folivores that spend most of their time resting or eating in the forest canopy. A three-toed sloth will, however, descend its tree weekly to defecate, which is risky, energetically costly and, until now, inexplicable. We hypothesized that this behaviour sustains an ecosystem in the fur of sloths, which confers cryptic nutritional benefits to sloths. We found that the more specialized three-toed sloths harboured more phoretic moths, greater concentrations of inorganic nitrogen and higher algal biomass than the generalist two-toed sloths. Moth density was positively related to inorganic nitrogen concentration and algal biomass in the fur. We discovered that sloths consumed algae from their fur, which was highly digestible and lipid-rich. By descending a tree to defecate, sloths transport moths to their oviposition sites in sloth dung, which facilitates moth colonization of sloth fur. Moths are portals for nutrients, increasing nitrogen levels in sloth fur, which fuels algal growth. Sloths consume these algae-gardens, presumably to augment their limited diet. These linked mutualisms between moths, sloths and algae appear to aid the sloth in overcoming a highly constrained lifestyle.
Assuntos
Comportamento Animal , Mariposas/fisiologia , Bichos-Preguiça/fisiologia , Simbiose , Fenômenos Fisiológicos da Nutrição Animal , Animais , Biomassa , Clorófitas/metabolismo , Clorófitas/fisiologia , Defecação , Ecossistema , Comportamento Alimentar , Herbivoria , Nitrogênio/análise , OviposiçãoRESUMO
Sparganothis sulfureana Clemens is a severe pest of cranberries in the Midwest and northeast United States. Timing for insecticide applications has relied primarily on calendar dates and pheromone trap-catch; however, abiotic conditions can vary greatly, rendering such methods unreliable as indicators of optimal treatment timing. Phenology models based on degree-day (DD) accrual represent a proven, superior approach to assessing the development of insect populations, particularly for larvae. Previous studies of S. sulfureana development showed that the lower and upper temperature thresholds for larval development were 10.0 and 29.9°C (49.9 and 85.8°F), respectively. We used these thresholds to generate DD accumulations specific to S. sulfureana, and then linked these DD accumulations to discrete biological events observed during S. sulfureana development in Wisconsin and New Jersey cranberries. Here, we provide the DDs associated with flight initiation, peak flight, flight termination, adult life span, preovipositional period, ovipositional period, and egg hatch. These DD accumulations represent key developmental benchmarks, allowing for the creation of a phenology model that facilitates wiser management of S. sulfureana in the cranberry system.
Assuntos
Mariposas/crescimento & desenvolvimento , Vaccinium macrocarpon , Animais , Feminino , Voo Animal , Masculino , OviposiçãoRESUMO
While bee-angiosperm mutualisms are widely recognized as foundational partnerships that have shaped the diversity and structure of terrestrial ecosystems, these ancient mutualisms have been underpinned by 'silent third partners': microbes. Here, we propose reframing the canonical bee-angiosperm partnership as a three-way mutualism between bees, microbes, and angiosperms. This new conceptualization casts microbes as active symbionts, processing and protecting pollen-nectar provisions, consolidating nutrients for bee larvae, enhancing floral attractancy, facilitating plant fertilization, and defending bees and plants from pathogens. In exchange, bees and angiosperms provide their microbial associates with food, shelter, and transportation. Such microbial communities represent co-equal partners in tripartite mutualisms with bees and angiosperms, facilitating one of the most important ecological partnerships on land.
Assuntos
Magnoliopsida , Microbiota , Abelhas , Animais , Simbiose , Pólen , Polinização , FloresRESUMO
Drosophila suzukii Matsumura (Diptera: Drosophilidae), commonly referred to as the spotted wing drosophila, is an exotic species that has proven a troublesome pest of fruit production in the United States. The fly targets small fruit and thus represents a concern for the U.S. cranberry industry. Two studies were conducted to assess whether cranberries may serve as hosts for D. suzukii. In the first study, the suitability of ripe, unripe, and over-ripe cranberries were assayed by examining adult oviposition and larval development in no-choice trials. In the second study, wounded and unwounded fruit were examined as potential hosts in choice and no-choice trials. Our first study showed that ripe, unripe, and over-ripe cranberries were unsuitable hosts (few eggs were laid, with no surviving puparia). In the wounded and unwounded berry study, no larvae survived to adulthood among unwounded berries. Within wounded fruit, D. suzukii readily fed and developed into adults. Together, these results suggest that unwounded cranberries--whether ripe, unripe, or over-ripe--are unsuitable as hosts for D. suzukii. Wounded rotting cranberries, however, can serve as hosts. Across the landscape, cranberry marshes with rotting fruit may contribute to D. suzukii source-sink dynamics.
Assuntos
Produtos Agrícolas/fisiologia , Drosophila/fisiologia , Oviposição , Vaccinium macrocarpon/fisiologia , Animais , Drosophila/crescimento & desenvolvimento , Feminino , Cadeia Alimentar , Frutas/fisiologia , Larva/crescimento & desenvolvimento , Larva/fisiologia , Óvulo/crescimento & desenvolvimento , Óvulo/fisiologia , Pupa/crescimento & desenvolvimento , Pupa/fisiologiaRESUMO
Greater resource use by diverse communities might result from species occupying complementary niches. Demonstrating niche complementarity among species is challenging, however, due to the difficulty in relating differences between species in particular traits to their use of complementary resources. Here, we overcame this obstacle by exploiting plastic foraging behavior in a community of predatory insects common on Brassica oleracea plants in Washington, USA. These predators complemented one another by partitioning foraging space, with some species foraging primarily along leaf edges and others at leaf centers. We hypothesized that emergent biodiversity effects would occur when predators partitioned foraging space on leaves, but not when spatial complementarity was dampened. Indeed, on intact leaves, edge- and center-foraging predators combined to kill more prey than any single predator species could by itself. These emergent diversity effects, however, disappeared on plants damaged by the caterpillar Plutella xylostella. Caterpillar chew-holes brought edge habitats to the center of leaves, so that all predator species could attack aphids anywhere on plants. With spatial niche differences diminished, there were no benefits of predator diversity; the most voracious single predator species killed the most aphids. Thus, caterpillar herbivory determined whether multi-predator-species effects reflected complementarity or species' individual impacts. Our study provides direct evidence for a causative relationship between niche differentiation and increased resource consumption by diverse communities, as revealed by ecological engineers that homogenize the foraging environment.
Assuntos
Biodiversidade , Insetos/fisiologia , Animais , Brassica , Larva/fisiologia , Folhas de Planta , Dinâmica Populacional , Comportamento PredatórioRESUMO
Developing bees derive significant benefits from the microbes present within their guts and fermenting pollen provisions. External microbial symbionts (exosymbionts) associated with larval diets may be particularly important for solitary bees that suffer reduced fitness when denied microbe-colonized pollen.To investigate whether this phenomenon is generalizable across foraging strategy, we examined the effects of exosymbiont presence/absence across two solitary bee species, a pollen specialist and generalist. Larvae from each species were reared on either microbe-rich natural or microbe-deficient sterilized pollen provisions allocated by a female forager belonging to their own species (conspecific-sourced pollen) or that of another species (heterospecific-sourced pollen). Our results reveal that the presence of pollen-associated microbes was critical for the survival of both the generalist and specialist larvae, regardless of whether the pollen was sourced from a conspecific or heterospecific forager.Given the positive effects of exosymbiotic microbes for larval fitness, we then examined if the magnitude of this benefit varied based on whether the microbes were provisioned by a conspecific forager (the mother bee) or a heterospecific forager. In this second study, generalist larvae were reared only on microbe-rich pollen provisions, but importantly, the sources (conspecific versus heterospecific) of the microbes and pollen were experimentally manipulated.Bee fitness metrics indicated that microbial and pollen sourcing both had significant impacts on larval performance, and the effect sizes of each were similar. Moreover, the effects of conspecific-sourced microbes and conspecific-sourced pollen were strongly positive, while that of heterospecific-sourced microbes and heterospecific-sourced pollen, strongly negative.Our findings imply that not only is the presence of exosymbionts critical for both specialist and generalist solitary bees, but more notably, that the composition of the specific microbial community within larval pollen provisions may be as critical for bee development as the composition of the pollen itself.
RESUMO
Microbial symbiosis drives physiological processes of higher-order systems, including the acquisition and consumption of nutrients that support symbiotic partner reproduction. Metabolic analytics provide new avenues to examine how chemical ecology, or the conversion of existing biomass to new forms, changes over a symbiotic life cycle. We applied these approaches to the nematode Steinernema carpocapsae, its mutualist bacterium, Xenorhabdus nematophila, and the insects they infect. The nematode-bacterium pair infects, kills, and reproduces in an insect until nutrients are depleted. To understand the conversion of insect biomass over time into either nematode or bacterium biomass, we integrated information from trophic, metabolomic, and gene regulation analyses. Trophic analysis established bacteria as meso-predators and primary insect consumers. Nematodes hold a trophic position of 4.6, indicative of an apex predator, consuming bacteria and likely other nematodes. Metabolic changes associated with Galleria mellonella insect bioconversion were assessed using multivariate statistical analyses of metabolomics data sets derived from sampling over an infection time course. Statistically significant, discrete phases were detected, indicating the insect chemical environment changes reproducibly during bioconversion. A novel hierarchical clustering method was designed to probe molecular abundance fluctuation patterns over time, revealing distinct metabolite clusters that exhibit similar abundance shifts across the time course. Composite data suggest bacterial tryptophan and nematode kynurenine pathways are coordinated for reciprocal exchange of tryptophan and NAD+ and for synthesis of intermediates that can have complex effects on bacterial phenotypes and nematode behaviors. Our analysis of pathways and metabolites reveals the chemistry underlying the recycling of organic material during carnivory. IMPORTANCE The processes by which organic life is consumed and reborn in a complex ecosystem were investigated through a multiomics approach applied to the tripartite Xenorhabdus bacterium-Steinernema nematode-Galleria insect symbiosis. Trophic analyses demonstrate the primary consumers of the insect are the bacteria, and the nematode in turn consumes the bacteria. This suggests the Steinernema-Xenorhabdus mutualism is a form of agriculture in which the nematode cultivates the bacterial food sources by inoculating them into insect hosts. Metabolomics analysis revealed a shift in biological material throughout progression of the life cycle: active infection, insect death, and conversion of cadaver tissues into bacterial biomass and nematode tissue. We show that each phase of the life cycle is metabolically distinct, with significant differences including those in the tricarboxylic acid cycle and amino acid pathways. Our findings demonstrate that symbiotic life cycles can be defined by reproducible stage-specific chemical signatures, enhancing our broad understanding of metabolic processes that underpin a three-way symbiosis.
Assuntos
Mariposas , Rabditídios , Xenorhabdus , Animais , Ecossistema , Triptofano , Insetos , Xenorhabdus/genética , Rabditídios/microbiologiaRESUMO
Cranberry fruitworm (Acrobasis vaccinii Riley (Lepidoptera: Pyralidae)) and blackheaded fireworm (Rhopobota naevana Hubner (Lepidoptera: Tortricidae)) threaten cranberry production annually by causing significant fruit damage. Up to four pesticide applications are made each year to control these insects, which are costly to producers and elevate pesticide residues in fruit. Pheromone-based mating disruption technology can provide control of these pests in cranberry production, with the potential to minimize, or eliminate, pesticide applications. In 2016, an uncrewed aerial vehicle (UAV) was investigated to apply a thick paraffin emulsion containing insect sex pheromones. Traditional agricultural equipment is not capable of applying the paraffin emulsion to cranberry beds due to the product's viscous, paste-like consistency. The first objective of this study was to retrofit an UAV (octocopter) with a novel extrusion device that had been engineered to deliver the pheromone-loaded paraffin at regular intervals during flight. The second objective was to confirm adequate distribution of the pheromones by measuring the mating disruption efficacy by monitoring male moth trap catches. The UAV was able to fly autonomously along a prescribed itinerary, deploying the paraffin product uniformly; however, the increased mass of the retrofitted UAV limited flight times to ~12 min. The number of male cranberry fruitworm and blackheaded fireworm moths caught in lure-baited traps were reduced in the paraffin-treated beds compared with untreated beds, indicating adequate distribution of the pheromones. The UAV-applied pheromones concept could be developed into a production scale application method in the future, although issues of battery life and lifting capacity will need to be resolved.
Assuntos
Mariposas , Atrativos Sexuais , Vaccinium macrocarpon , Animais , Controle de Insetos , Feromônios , Comportamento Sexual AnimalRESUMO
Consumer diversity generally increases resource consumption. Consumers can also impact other species by altering their behavior, but it is unclear how such nonconsumptive effects scale with diversity. We independently manipulated predator species richness and the consumptive and nonconsumptive effects of predator communities to measure the role of each factor in protecting Brassica oleracea plants from caterpillar herbivory. Plant biomass was greatest when diverse predator assemblages induced antipredator behaviors in herbivores, an effect not further strengthened when predators could also kill caterpillars. Predators within diverse communities were more likely to forage on plants and to disrupt herbivore feeding, reflecting greater aversion to foraging among conspecific than heterospecific competitors. Predator diversity, therefore, initiated behavioral changes at the predator and then herbivore trophic levels, both to the benefit of plants. Our results indicate that strong, emergent species-richness effects can be transmitted entirely through behavioral interactions, independent of resource consumption.
Assuntos
Biodiversidade , Insetos/fisiologia , Comportamento Predatório/fisiologia , AnimaisRESUMO
The spotted-wing drosophila, Drosophila suzukii Matsumura, is an exotic species in North America and represents a major threat to fruit production. Efforts to manage D. suzukii have focused primarily on insecticides, but such controls may, at times, be unreliable, given that D. suzukii larvae are often ensconced within fruit. The fruit interior, however, may represent suitable foraging substrates for carnivorous/entomopathogenic nematodes. In preliminary trials, a rare nematode species, Oscheius onirici Torrini et al., was shown to be highly virulent against D. suzukii when the nematodes were applied directly to fly larvae. To address the more important question of whether this nematode would be as virulent when applied to fruit, we set up assays in which blueberries were infested with D. suzukii larvae and then sprayed with O. onirici infective juveniles (IJs). Across two laboratory trials, O. onirici IJs suppressed D. suzukii puparia by 78.2%. Oscheius onirici IJs were able to search effectively within fruit substrates, find the fly larvae therein, and kill the flies before they could pupariate. Oscheius onirici, therefore, may represent a viable new bio-control agent for D. suzukii management and should be field-tested across a broader diversity of cropping systems.
Assuntos
Inseticidas , Rabditídios , Animais , Drosophila , Frutas , Controle de Insetos , América do NorteRESUMO
The pollen stores of bumble bees host diverse microbiota that influence overall colony fitness. Yet, the taxonomic identity of these symbiotic microbes is relatively unknown. In this descriptive study, we characterized the microbial community of pollen provisions within captive-bred bumble bee hives obtained from two commercial suppliers located in North America. Findings from 16S rRNA and ITS gene-based analyses revealed that pollen provisions from the captive-bred hives shared several microbial taxa that have been previously detected among wild populations. While diverse microbes across phyla Firmicutes, Proteobacteria, Bacteroidetes, Actinobacteria, and Ascomycota were detected in all commercial hives, significant differences were detected at finer-scale taxonomic resolution based on the supplier source. The causative agent of chalkbrood disease in honey bees, Ascosphaera apis, was detected in all hives obtained from one supplier source, although none of the hives showed symptoms of infection. The shared core microbiota across both commercial supplier sources consisted of two ubiquitous bee-associated groups, Lactobacillus and Wickerhamiella/Starmerella clade yeasts that potentially contribute to the beneficial function of the microbiome of bumble bee pollen provisions.
RESUMO
Although solitary bees provide crucial pollination services for wild and managed crops, this species-rich group has been largely overlooked in pesticide regulation studies. The risk of exposure to fungicide residues is likely to be especially high if the spray occurs on, or near host plants while the bees are collecting pollen to provision their nests. For species of Osmia that consume pollen from a select group of plants (oligolecty), the inability to use pollen from non-host plants can increase their risk factor for fungicide-related toxicity. This manuscript describes protocols used to successfully rear oligolectic mason bees, Osmia ribifloris sensu lato, from egg to prepupal stage within cell culture plates under standardized laboratory conditions. The in vitro-reared bees are subsequently used to investigate the effects of fungicide exposure and pollen source on bee fitness. Based on a 2 × 2 fully crossed factorial design, the experiment examines the main and interactive effects of fungicide exposure and pollen source on larval fitness, quantified by prepupal biomass, larval developmental time, and survivorship. A major advantage of this technique is that using in vitro-reared bees reduces natural background variability and allows the simultaneous manipulation of multiple experimental parameters. The described protocol presents a versatile tool for hypotheses testing involving the suite of factors affecting bee health. For conservation efforts to be met with significant, lasting success, such insights into the complex interplay of physiological and environmental factors driving bee declines will prove to be critical.
Assuntos
Abelhas/química , Larva/química , Polinização/fisiologia , Animais , Fatores de RiscoRESUMO
The differential discrimination of nitrogen isotopes (15N/14N) within amino acids in consumers and their diets has been routinely used to estimate organismal tropic position (TP). Analogous isotopic discrimination can occur within plants, particularly in organs lacking chloroplasts. Such discrimination likely arises from the catabolic deamination of amino acids, resulting in a numerical elevation of estimated TP, within newly synthesized biomass. To investigate this phenomenon, we examined the 15N/14N of amino acids (δ15 NAA) in spring leaves and flowers from eight deciduous and two annual plants. These plants were classified on the basis of their time of bloom, plants that bloomed when their leaves were absent (Type I) versus plants that bloomed while leaves were already present (Type II). Based on the δ15 NAA values from leaves, both plant types occupied comparable and ecologically realistic mean TPs (=1.0 ± 0.1, mean ± 1σ). However, the estimated TPs of flowers varied significantly (Type I: 2.2 ± 0.2; Type II: 1.0 ± 0.1). We hypothesize that these results can be interpreted by the following sequence of events: (1) Type I floral biomass is synthesized in absence of active photosynthesis; (2) the catabolic deamination of amino acids in particular, leaves behind 15N in the residual pool of amino acids; and (3) the incorporation of these 15N-enriched amino acids within the biomass of Type I flowers results in the numerical elevation of the TPs. In contrast, the actively photosynthesizing Type II leaves energetically sustain the synthesis of Type II flower biomass, precluding any reliance on catabolic deamination of amino acids. Amino acids within Type II flowers are therefore isotopically comparable to the Type II leaves. These findings demonstrate the idiosyncratic nature of the δ15 NAA values within autotrophic organs and have implications for interpreting trophic hierarchies using primary producers and their consumers.
RESUMO
Soybean aphid (Aphis glycines Matsumura) is a pest of soybean in the northern Midwest whose migratory patterns have been difficult to quantify. Improved knowledge of soybean aphid overwintering sites could facilitate the development of control efforts with exponential impacts on aphid densities on a regional scale. In this preliminary study, we explored the utility of variation in stable isotopes of carbon and nitrogen to distinguish soybean aphid overwintering origins. We compared variation in bulk 13C and 15N content in buckthorn (Rhamnus cathartica L.) and soybean aphids in Wisconsin, among known overwintering locations in the northern Midwest. Specifically, we looked for associations between buckthorn and environmental variables that could aid in identifying overwintering habitats. We detected significant evidence of correlation between the bulk 13C and 15N signals of soybean aphids and buckthorn, despite high variability in stable isotope composition within and among buckthorn plants. Further, the 15N signal in buckthorn varied predictably with soil composition. However, lack of sufficient differentiation of geographic areas along axes of isotopic and environmental variation appears to preclude the use of carbon and nitrogen isotopic signals as effective predictors of likely aphid overwintering sites. These preliminary data suggest the need for future work that can further account for variability in 13C and 15N within/among buckthorn plants, and that explores the utility of other stable isotopes in assessing likely aphid overwintering sites.
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Growers often use fungicide sprays during bloom to protect crops against disease, which exposes bees to fungicide residues. Although considered "bee-safe," there is mounting evidence that fungicide residues in pollen are associated with bee declines (for both honey and bumble bee species). While the mechanisms remain relatively unknown, researchers have speculated that bee-microbe symbioses are involved. Microbes play a pivotal role in the preservation and/or processing of pollen, which serves as nutrition for larval bees. By altering the microbial community, it is likely that fungicides disrupt these microbe-mediated services, and thereby compromise bee health. This manuscript describes the protocols used to investigate the indirect mechanism(s) by which fungicides may be causing colony decline. Cage experiments exposing bees to fungicide-treated flowers have already provided the first evidence that fungicides cause profound colony losses in a native bumble bee (Bombus impatiens). Using field-relevant doses of fungicides, a series of experiments have been developed to provide a finer description of microbial community dynamics of fungicide-exposed pollen. Shifts in the structural composition of fungal and bacterial assemblages within the pollen microbiome are investigated by next-generation sequencing and metagenomic analysis. Experiments developed herein have been designed to provide a mechanistic understanding of how fungicides affect the microbiome of pollen-provisions. Ultimately, these findings should shed light on the indirect pathway through which fungicides may be causing colony declines.