Solitary Bee Osmia Lignaria Research Articles

Effect of protein and lipids in pollen on the developmental success of the native solitary bee Osmia lignaria Say

The health of solitary bees is dependent on the pollen they consume, driving their development from larvae to pupae. Nutrients such as proteins and lipids play an important role in bee development and could be an important key in conservation efforts to support declining populations. We examined the concentration of protein, total lipids, and 13 individual lipid classes in pollen provisions collected from the native solitary nesting bee, Osmia lignaria Say, at 22 sites in urban and rural landscapes in western Washington over three years and during two distinct foraging periods. The results indicate that protein concentrations in pollen did not significantly affect larval development. We detected higher lipid concentrations in the second foraging period, which was also associated with increased larval developmental success. Using Next-Generation sequencing on collected pollen, we also ascertained the plant genera in pollen and observed that plant richness did not differ significantly between the two foraging periods even though levels of lipid concentrations did. Individual lipid classes may play a role in the successful development of O. lignaria, as hexosylceramide and cholesterol ester were positively associated with O. lignaria larval developmental success, which emphasizes the need for additional studies on the role of individual lipid classes on bee development.

Metabolic and transcriptomic characterization of summer and winter dormancy in the solitary bee, Osmia lignaria

The solitary bee Osmia lignaria is a native pollinator in North America with growing economic importance. The life cycle of O. lignaria provides a unique opportunity to compare the physiological and molecular mechanisms underlying two ecologically contrasting dormancies within the same species. O. lignaria prepupae become dormant during the summer to avoid high temperatures. Shortly after adult eclosion, they enter a second dormancy and overwinter as diapausing adults. To compare these two dormancies, we measured metabolic rates and gene expression across development as bees initiate, maintain, and terminate both prepupal (summer) and adult (overwintering) dormancies. We observed a moderate temperature-independent decrease in gas exchange during both the prepupal dormancy after cocoon spinning (45 %) and during adult diapause after eclosion (60 %). We sequenced and assembled a high-quality reference genome from a single haploid male bee with a contiguous n50 of 5.5 Mbp to facilitate our transcriptomic analysis. The transcriptomes of dormant prepupae and diapausing adults clustered into distinct groups more closely associated with life stage than dormancy status. Membrane transport, membrane-bound cellular components, oxidoreductase activity, glutathione metabolism, and transcription factor activity increased during adult diapause, relative to prepupal dormancy. Further, the transcriptomes of adults in diapause clustered into two groups, supporting multiple phases of diapause during winter. Late adult diapause was associated with gene expression profiles supporting increased insulin/IGF, juvenile hormone, and ecdysone signaling.

Flower plantings support wild bee reproduction and may also mitigate pesticide exposure effects

Abstract Sustainable agriculture relies on pollinators, and wild bees benefit yield of multiple crops. However, the combined exposure to pesticides and loss of flower resources, driven by agricultural intensification, contribute to declining diversity and abundance of many bee taxa. Flower plantings along the margins of agricultural fields offer diverse food resources not directly treated with pesticides. To investigate the potential of flower plantings to mitigate bee pesticide exposure effects and support bee reproduction, we selected replicated sites in intensively farmed landscapes where half contained flower plantings. We assessed solitary bee Osmia lignaria and bumble bee Bombus vosnesenskii nesting and reproduction throughout the season in these landscapes. We also quantified local and landscape flower resources and used bee‐collected pollen to determine forage resource use and pesticide exposure and risk. Flower plantings, and their local flower resources, increased O. lignaria nesting probability. Bombus vosnesenskii reproduction was more strongly related to landscape than local flower resources. Bees at sites with and without flower plantings experienced similar pesticide risk, and the local flowers, alongside flowers in the landscape, were sources of pesticide exposure particularly for O. lignaria. However, local flower resources mitigated negative pesticide effects on B. vosnesenskii reproduction. Synthesis and applications. Bees in agricultural landscapes are threatened by pesticide exposure and loss of flower resources through agricultural intensification. Therefore, finding solutions to mitigate negative effects of pesticide use and flower deficiency is urgent. Our findings point towards flower plantings as a potential solution to support bee populations by mitigating pesticide exposure effects and providing key forage. Further investigation of the balance between forage benefits and added pesticide risk is needed to reveal contexts where net benefits occur.

Comparison of Pollen Grain Treatments Without Mechanical Fracturation Prior to Protein Quantification.

Protein and amino acids in pollen are important nutritional components for larval development in several insect species, especially in Apoidea. The Bradford assay is a widely used method to measure relative protein content of pollen, which can shed light on pollen quality and consequences to fitness. Prior to using the Bradford assay, protein must be released from pollen grains, often using a mixture of chemical and mechanical fracturation methods. In this study, we tested the efficacy of protein extraction without using mechanical fracturation. We used pollen collected by the solitary bee Osmia lignaria Say to compare two known buffers associated with pollen protein analysis: phosphate-buffered saline and sodium hydroxide, and deionized water, and with different pollen weights from which we quantified protein using the Bradford assay. While all buffers and deionized water were useful in releasing protein from pollen grains collected by O. lignaria, the use of sodium hydroxide resulted in significantly higher protein quantification across all pollen weights. This methodological study can inform future studies of pollen nutrition in pollen-foraging species.

Pre‐wintering conditions and post‐winter performance in a solitary bee: does diapause impose an energetic cost on reproductive success?

1. Diapause is a dynamic process of low metabolic activity that allows insects to survive periods of harsh conditions. Notwithstanding the lowered metabolism, and because diapausing insects have no access to food, diapause has an energetic cost that may affect post‐diapause performance.2. Previous studies on the solitary bee Osmia lignaria have shown that prolonged pre‐wintering periods (the time during which individuals already in diapause remain at warm temperatures) are associated with elevated lipid consumption, fat body depletion, and body weight loss. The present study investigated whether prolonged pre‐wintering also affects reproduction, i.e. whether the costs associated with diapause could have an effect on post‐diapause performance in this species.3. Females were exposed to a range of pre‐wintering conditions, and ovary development and individual post‐wintering performance were monitored throughout their adult life span.4. No evidence of an effect of pre‐wintering duration on post‐diapause reproductive success was found. Expected differences in the timing of establishment were not observed because ovary maturation was, surprisingly, not arrested during pre‐wintering. Prolonged pre‐wintering duration did not result in decreased life span, probably because emerging females could rapidly replenish their metabolic reserves through feeding. However, there was a very strong effect of the duration of the pre‐emergence period on the likelihood of nest establishment.5. Longevity, the main factor determining fecundity in Osmia, is subjected to high levels of intrinsic variability, even among females of similar size exposed to identical conditions during development and nesting.

Reproduction and survival of a solitary bee along native and exotic floral resource gradients

Native bee abundance has long been assumed to be limited by floral resources. This paradigm has been established in large measure because more bees are often found in areas supporting greater floral abundance. This could result from attraction to resource-rich sites as well as greater local demographic performance in sites supporting high floral abundance; however, demographic performance is usually unknown. Factors other than floral resources such as availability of nest sites, pressure from natural enemies, or whether floral resources are from a mixed native or mostly monodominant exotic assemblage might influence survival or fecundity and hence abundance. We examined how the survival and fecundity of the native solitary bee Osmia lignaria varied along a gradient in floral resource abundance. We released bees alongside a nest block at 27 grassland sites in Montana (USA) that varied in floral abundance and the extent of invasion by exotic forbs. We monitored nest construction and the fate of offspring within each nest. The number of nests established was positively related to native forb abundance and was negatively related to exotic forb species richness. Fecundity was positively related to native forb species richness; however, offspring mortality caused by the brood parasite Tricrania stansburyi was significantly greater in native-dominated sites. These results suggest that native floral resources can positively influence bee populations, but that the relationship between native floral resources and bee population performance is not straightforward. Rather, bees may face a trade-off between high offspring production and low offspring survival in native-dominated sites.

The long summer: Pre-wintering temperatures affect metabolic expenditure and winter survival in a solitary bee

The impact of climate change on insect populations depends on specific life cycle traits and physiological adaptations. The solitary bee Osmia lignaria winters as a pre-emergent adult, and requires a period of cold temperature for winter diapause completion. It is a univoltine species, and diapause induction does not depend on photoperiod. To understand the potential effects of longer summers on O. lignaria populations, we exposed individuals to three treatments simulating early, mid and late winter arrivals, and measured respiration rates, metabolic expenditure, weight loss, fat body depletion, lipid levels and winter mortality. The early-winter treatment disrupted diapause development, but had no apparent negative effects on fitness. In contrast, late-winter bees had a greater energetic expenditure (1.5-fold), weight (1.4-fold) and lipid (2-fold) loss, greater fat body depletion, and a 19% increase in mortality compared to mid-winter bees. We also monitored adult eclosion and arrival of winter temperatures under natural conditions in four years. We found a positive correlation between mean degree-day accumulation during pre-wintering (a measure of asynchrony between adult eclosion and winter arrival) and yearly winter mortality. Individually, bees experiencing greater degree-day accumulations exhibited reduced post-winter longevity. Timing of adult eclosion in O. lignaria is dependent on the duration of the prepupal period, which occurs in mid-summer, is also diapause-mediated, and is longer in populations from southerly latitudes. In a global warming scenario, we expect long summer diapause phenotypes to replace short summer diapause phenotypes, effectively maintaining short pre-wintering periods in spite of delayed winter arrivals.

Timing of eclosion affects diapause development, fat body consumption and longevity in Osmia lignaria, a univoltine, adult-wintering solitary bee

Most insects from temperate areas enter diapause ahead of winter. Species diapausing in a feeding stage and accumulating metabolic reserves during permissive pre-wintering conditions are expected to enter diapause shortly before the onset of winter. In contrast, species diapausing in a non-feeding stage are expected to lower their metabolism as soon as possible to avoid excessive consumption of metabolic reserves. The solitary bee Osmia lignaria winters as a non-feeding adult within its cocoon, but previous studies show important weight losses and increased winter mortality in populations pre-wintered for extended periods. We measured respiration rates to assess diapause initiation and maintenance during pre-wintering, and tested whether timing of adult eclosion affected fitness by measuring fat body depletion, winter mortality and post-winter longevity. We worked with different cohorts of a population reared under natural conditions, and manipulated pre-wintering duration in a population reared under artificial conditions. In agreement with our expectation, O. lignaria lower their metabolic rates within a few days of adult eclosion, but nonetheless suffer strong weight loss during pre-wintering. Early developing individuals suffer greater weight loss and fat body depletion, and have short post-winter longevity. Although, we found no differences in winter mortality among treatments, our results indicate that increased mortality may occur in years with late winter arrivals. We discuss fundamental ecophysiological differences between adult and prepupal diapause within the Megachilidae, and hypothesize that species wintering as adults will be more negatively affected by a situation of extended summers under a scenario of global warming.

RESOURCE DISTRIBUTIONS AMONG HABITATS DETERMINE SOLITARY BEE OFFSPRING PRODUCTION IN A MOSAIC LANDSCAPE

Within mosaic landscapes, many organisms depend on attributes of the environment that operate over scales ranging from a single habitat patch to the entire landscape. One such attribute is resource distribution. Organisms' reliance on resources from within a local patch vs. those found among habitats throughout the landscape will depend on local habitat quality, patch quality, and landscape composition. The ability of individuals to move among complementary habitat types to obtain various resources may be a critical mechanism underlying the dynamics of animal populations and ultimately the level of biodiversity at different spatial scales. We examined the effects that local habitat type and landscape composition had on offspring production and survival of the solitary bee Osmia lignaria in an agri-natural landscape in California (U.S.A.). Female bees were placed on farms that did not use pesticides (organic farms), on farms that did use pesticides (conventional farms), or in seminatural riparian habitats. We identified pollens collected by bees nesting in different habitat types and matched these to pollens of flowering plants from throughout the landscape. These data enabled us to determine the importance of different plant species and habitat types in providing food for offspring, and how this importance changed with landscape and local nesting-site characteristics. We found that increasing isolation from natural habitat significantly decreased offspring production and survival for bees nesting at conventional farms, had weaker effects on bees in patches of seminatural habitat, and had little impact on those at organic farm sites. Pollen sampled from nests showed that females nesting in both farm and seminatural habitats relied on pollen from principally native plant species growing in seminatural habitat. Thus connectivity among habitats was critical for offspring production. Females nesting on organic farms were buffered to isolation effects by switching to floral resources growing at the farm site when seminatural areas were too distant. Overall local habitat conditions (farm management practices) can help bolster pollinators, but maintaining functional connectivity among habitats will likely be critical for persistence of pollinator populations as natural habitats are increasingly fragmented by human activities.

Bee Population Returns and Cherry Yields in an Orchard Pollinated with Osmia lignaria (Hymenoptera: Megachilidae)

During 1998–2003, we used populations of the solitary bee Osmia lignaria Say to pollinate a commercial sweet cherry orchard in northern Utah. Bee densities released each year ranged from 1290 to 1857 females/ha, with approximately twice as many males. Female progeny produced each year were greater than parental populations released, except in 2003, when nesting was poor due to bird predation. Despite poor weather during bloom, and in contrast to most other local producers, the study orchard produced harvestable crops in 1999 (2,964 kg/ha) and 2001 (3,154 kg/ha). In 1998 and 2000, record yields were obtained (10,625 and 12,096 kg/ha, respectively). Including only those years with harvestable crops, average production was 2.2 times higher in 1998–2003 (when O. lignaria populations were used) compared with 1992–1997 (when 10 Apis mellifera hives were used). This is the first study reporting multiyear cherry yields in an orchard pollinated with O. lignaria in North America.

Bee Population Returns and Cherry Yields in an Orchard Pollinated with <I>Osmia lignaria</I> (Hymenoptera: Megachilidae)

During 1998-2003, we used populations of the solitary bee Osmia lignaria Say to pollinate a commercial sweet cherry orchard in northern Utah. Bee densities released each year ranged from 1290 to 1857 females/ha, with approximately twice as many males. Female progeny produced each year were greater than parental populations released, except in 2003, when nesting was poor due to bird predation. Despite poor weather during bloom, and in contrast to most other local producers, the study orchard produced harvestable crops in 1999 (2,964 kg/ha) and 2001 (3,154 kg/ha). In 1998 and 2000, record yields were obtained (10,625 and 12,096 kg/ha, respectively). Including only those years with harvestable crops, average production was 2.2 times higher in 1998-2003 (when O. lignaria populations were used) compared with 1992-1997 (when 10 Apis mellifera hives were used). This is the first study reporting multiyear cherry yields in an orchard pollinated with O. lignaria in North America.

Olfactory cues and nest recognition in the solitary bee Osmia lignaria

Abstract. The use of olfactory cues for nest recognition by the solitary bee Osmia lignaria is studied in a greenhouse environment. Glass tubes are provided as nesting cavities to allow the in‐nest behaviour of bees to be observed. In addition, each glass tube is cut into three sections for experimental manipulation and for subsequent chemical analysis. Nesting females drag their abdomen along the tube before exiting, spiral inside the tube, and sometimes deposit fluid droplets from the tip of the abdomen. For the manipulation, the outer section, the middle section, or both sections are removed and replaced with similar clean glass tube sections, and the behaviour exhibited by test females is recorded upon arrival in front of the nesting site and inside the nesting tubes. The resulting hesitation behaviour displayed by females after treatments appears to indicate the loss of some olfactory cues used for nest recognition inside the entire nest. Chemical analysis of the depositions inside the nesting tube, as well as analysis of the cuticular lipids of the nesting bees, reveals the presence of free fatty acids, hydrocarbons and wax esters.

Effect of Temperature on <I>Osmia lignaria</I> (Hymenoptera: Megachilidae) Prepupa–Adult Development, Survival, and Emergence

The solitary bee Osmia lignaria Say continues to be developed as an orchard pollinator in the United States and southern Canada. Female bees are active during the early spring and construct nests consisting of a linear series of unlined cells delimited by mud partitions. Cells are provisioned with a pollen/nectar mass on which an egg is deposited, and nests are sealed with a mud plug. In 1997, we initiated two experiments on the development, mortality, and emergence of O. lignaria at selected laboratory temperature regimes and outdoors. In the first experiment (published previously), we compared temperature treatments for their adequacy in maintaining healthy O. lignaria populations. In a second experiment (reported here), we determined the relationship between rearing temperatures and prepupa-adult development rates as well as emergence time and longevity after wintering and incubation the following spring. We observed important differences in O. lignaria prepupa versus pupa responses to selected temperature treatments. The relationship between temperature and days to pupa was U-shaped, with additional time to transit the prepupa-pupa interval at temperatures above and below 26 degrees C. The negative relationship between temperature and the length of the pupa to adult interval contrasts with the U-shaped thermal response observed for prepupae. Thus, with each increase in thermal heat units over the range of temperature treatments tested, we observed an additional reduction in the pupa-adult interval. Individuals reared at constant 18 degrees C required 2.4 times as many days to transit the pupa-adult interval compared with those at constant 32 degrees C. Our results suggest that there is a need for the development of regionally adapted, latitude-specific breeding populations of this outstanding orchard crop pollinator.

Development and Emergence of the Orchard PollinatorOsmia lignaria(Hymenoptera: Megachilidae)

Abstract The solitary bee Osmia lignaria Say has been developed as an orchard pollinator in the western United States. Immatures develop through the spring and summer. By late summer, bees become adults and remain in this stage inside their cocoons throughout the winter. In this study, we reared O. lignaria at various temperature regimes in the laboratory and outdoors. Developmental rates increased with temperature: bees reared at 18°C took >120 d to complete development, whereas bees reared at 29°C took half that long. Bees reared outdoors under fluctuating ambient conditions took ≈95 d. At 18°C, some bees were unable to complete prepupal dormancy. Different developmental stages responded differently to the various temperature regimes. Fluctuating temperatures averaging 22°C significantly shortened the dormant prepupal stage, and, as a result, bees developed faster than at the equivalent constant temperatures. Bees that developed faster (29°C and fluctuating temperatures) could be wintered as early as Au...