Rangeland Pollinator Management Important to Maintaining Healthy Ecosystems

While pollinator management has become a reality for those working in agricultural areas, it is also a very important part of maintaining healthy rangeland ecosystems. Hoffman Black et al. demonstrate the important role pollinators, especially bees, play in maintaining food cycles in wild rangeland as well as their benefits to adjacent agricultural areas. Given the threats urbanization, insecticides and pathogens pose to today’s bee species, rangeland pollinator management is an opportunity to provide refuge for vulnerable bee populations and the flora and fauna that depend upon them. While evidence suggests declines in wild and domesticated bee populations, these researchers argue providing wild rangelands as a safe habitat may help slow this trend.–Michael Landsman
Hoffman Black, S., Shepard, M., Vaughan, M., Rangeland management for pollinators.  Rangelands, 33(3):9-13. 2011.

            Hoffman et al. argue bees and rangelands have a symbiotic relationship which should be supported to maintain bee population numbers. In California, for example, shrubland and scrub habitats in rangelands provide important shelter for dwindling bee populations. In fact, chaparral communities have some of the highest levels of bee diversity per unit in the world. Thus, resource management in rangelands must take into account the health of the pollinator populations. Hoffman et al. look at issues of grazing, prescribed burns and herbicide applications.
            In recent years, researchers have discovered strong links between unsustainable grazing practices and drops in bee populations. Uncontrolled sheep grazing in the Sierra Nevada rangelands has been shown to decimate host-plant species enough to nearly eliminate bee pollinator communities. Scientists have also suggested insects in the Southwest have not developed alongside large ungulates and introducing buffalo or other species into these rangelands can put severe pressure on pollinators. However, Hoffman et al. argue grazing can play an important role in rangeland ecosystems as long as it is managed, with enough time between grazing periods to replenish plant-pollinator numbers.
            While prescribed burns have long been a part of natural management in US prairie systems, they have the capacity to decimate bee populations. Burning in small, isolated habitat fragments has been shown to have a consistently negative effect on bee population numbers, given the inability for colonizers to reach these areas and replenish them. Butterflies, another important pollinator species, have also been observed to be negatively effected by widespread burns. This article calls for more responsibility in planning fires, allowing colonizers to return to the area so as not to indiscriminately remove all pollinating species. It can take two to three years for a pollinator species to fully recover from a large prescribed burn, given how isolated the area is.
            Finally, this paper takes issue with the harm herbicides have caused natural pollinator species. The widespread use of nonselective herbicides has been shown to kill the floral species upon which bees are dependent. Numerous studies over recent years have shown higher levels of invertebrates in unsprayed plots than those treated with herbicides. Kevan et al. linked rapid bee loss in France to the loss Asteraceae and Lamiaceae flowers due to indiscriminate herbicide spraying. Furthermore, the same paper observed how herbicides killed many of the plants important to blueberry pollinators, reducing their numbers as well. Hoffman et al. argue for the use of selective herbicides along with a mechanical management of shrubs and small trees which provide shelter for plant-pollinators. They also argue for minimal spraying in rangelands, allowing as much of the wild, untreated ecosystem to remain. Thus, natural resource management in rangelands should prioritize policies which preserve plant pollinators. 

New Study Finds Great Complexity in Synchrony Between Pollinators and Plants in Rocky Mountains

Given that global climate warming has been observed in many different ecosystems as a possible cause of phenological mismatch between mutualistic species, the acute threat such mismatch presents to pollinators and their host species has provoked a number of studies in the last few years. Forest and Thomson (2011) performed a study of synchrony between bee species and flowers in the Rocky Mountains over the course of three years which provides important insights into the understanding of what causes phenological mismatches. Unlike previous plant-pollinator research projects, Forest and Thomson were able to decouple bee flight data from flower phenology by observing bees at custom-built nests rather than at their host-plants. These trap-nests were placed across an altitude gradient on a mountain slope and monitored for seasonal emergence over the course of three years. Using this observational data, the researches created phenology models to compare plant and bee  emergence and concluded local environmental conditions are the key regulators for both flora and fauna, and while both bees and plants showed capacity for variation, plants are more likely to advance phenological response to rising temperatures earlier in the spring.
Forrest, J., Thomson, James., 2011. An examination of synchrony between insect emergence and flowering in Rocky Mountain meadows. Ecological Monographts, 81. 3., pp. 469-491.

            There exists abundant evidence that global climate warming has caused phenological advancement in many individual species worldwide. However, little research has been done to verify temporal mismatches between pollinators and host plants; major mismatches could be fatal for ecosystems which rely on bee pollinators. While both bees and plant depend on temperature to determine the beginning of foraging and blooming respectively, researchers have also observed a host of other possible factors. For example, researchers have observed photoperiod changes as an important factor in provoking blooming. Furthermore, some plants require passing through a period of cold temperatures before flowering; this so-called “chilling requirement” complicates simple degree-day models for predicting phenological advances in these plants. Finally, many mountain plants’ blooms are closely correlated to snowmelt. Insect development rate is also closely related to temperature and thus degree-day models have been used to predict bee phenology. However the challenge in collecting unbiased bee data lies in the fact that researchers have historically observed bees at flowers, which makes such data dependent on plant phenology. Thus, Forrest and Thomson seek to study insect phenology independent of plant behavior.
            In order to achieve this, the researchers studied bee and wasp phenology in the subalpine Rocky Mountains across an altitudinal gradient in an area where plant phenology is believed to be closely tied to the annual snowmelt. To decouple bee data from plant data, the researchers created artificial “trap nests” with monitoring equipment to follow both the temperature of the nests throughout the year as well as when the bees were emerging in the spring. Thus, they were able to directly observe potential changes in bee phenology without relying on plant behavior. While the elevational gradient of the fourteen sites was only 350 m, it encompassed a wide variety of environmental and phenological diversity. After the initial season in 2007, researchers switched the colonies from the highest latitude and lowest latitude as switching the boxes which were higher and lower to the ground. Therefore they were able to isolate the environmental influences from the genotypic behaviors of the various bee species being researched.
            Upon completion of the study, researchers found temperature to be the best predictor of phenological advance in bee species. In fact, using a degree-day model they were able to predict the peak dates of flowering and bee flight with significant accuracy for the 2008 season. With regards to the transplant experiment from higher and lower altitudes, results suggested there was no effect of site origin on mean emergence dates for the species studied. The nest height study also showed similar results, with average temperatures being similar after snowmelt and the lower level nests were no longer snowcapped. Snowmelt was ruled out as a major phenological factor because all traps were snow covered the first winter in 2007, however the next two years saw such light snowfall that none of the nests were covered through winter. Researchers conclude that temperature is the biggest factor in determining bee phenology and while both the bees and plants in the study area demonstrate capacity to vary with climate change, further research is required to assess the risk of major mismatch. 

Climate Warming, CO2 Levels and Nitrogen Deposition Interact to Threaten Plant/Pollinator Mutualism

As global ecosystems face unprecedented environmental change from increases in temperature, CO2, and nitrogen levels,  mutualist relationships such as those between plants and their pollinators have come under particular threat. Each of the three aforementioned variables have been demonstrated to alter healthy . plant/pollinator relationships either through phenological mismatch, reductions in pollinator diversity or the inability of pollinators to locate host plants. Hoover et al. (2012) breaks new ground in the study of environmental factors on pollinator mutualism by looking at the interactive effects of temperature, CO2 levels and N deposition upon the relationship between bumble bees and a species of pumpkin flower in a controlled experiment. The results demonstrated unique interactive impacts on flower morphology, phenology and nectar composition, with bees choosing nectars high in N levels which reduce worker bee longevity rates. Thus, Hoover et al. have demonstrated an important new possible threat to bees and their host plants with regards to climate change.
Hoover, S., Ladley, J., Shchepetkina, A., Tisch, M., Gieseg, S., Tylianakis, J., 2012 Warming, CO2, and nitrogen deposition interactively affect a plant-pollinator mutualism. Ecology Letters, 15. 227-234.

            Hoover et al. designed an experiment to study the interactive impact of three major components of climate change on plant/pollinator mutualism. For a host plant, they chose the pumpkin because it depends strongly on bee pollination, are cultivated globally and have large, unisexual flowers capable of producing significant nectar for testing. Researchers grew the pumpkin plants under controlled conditions and created eight treatment combinations with either ambient or elevated levels of temperature, CO2 or N deposition based on average current of future predicted levels. All plants were given the same levels of light and water and the onset of flowering as well as physical attributes were recorded. Next, researchers extracted nectar from the test plants and studied the chemical composition of each sample. To test for bee reaction, Hoover et al. created synthetic nectars by adding sugar and amino acid standards to water and observed bee behavior, recording the amount of nectar consumed after each visit.
            The results of the experiment suggest interactivity between temperature increase, CO2 levels and N deposition impact plant/pollinator relationships. Plants which received increased levels of N and temperature produced larger flowers and at a higher frequency than plants exposed to higher CO2 levels rather than temperature, which caused smaller flowers to bloom. N was observed to increase flower diameter while temperature caused a decrease. With regards to phenology, elevated N and temperature caused flowers to bloom earlier by an average of 15.8 days while increased CO2 was observed to delay blooming by about ten days. Interactions between the three factors also changed the sugar levels and chemical compositions of nectar in ways which, individually, they otherwise would not.
            With regards to bee preference, researchers found a nonsignificant tendency for the species to prefer the nectar with increased levels of N. Bees also preferred the nectar with high N and elevated CO2 levels but not with high N and high temperature. Furthermore, bees also were drawn to the nectar which represented high levels of all three factors. While bees were drawn overall to nectar with higher levels of N, these nitrogen levels were shown to decrease bee longevity by an average of eight days. Higher CO2 levels also reduced bee longevity by an average of about two days. Finally, higher concentrations of sugar in the nectar brought about by N levels was also demonstrated to negatively impact bee longevity.
            The results of this study demonstrate a significant threat to bee and host plant relationships from combinatorial affects of drivers of climate change. Different combinations of elevated temperature, CO2 and N levels were seen to impact the physical structure of plant flowers which determine attractiveness to pollinators. Furthermore, demonstrated phenological changes run the risk of causing a mismatch between bees and their host plants. A threat of phenological mismatch becomes more severe when paired with the fact that bees chose nectars with higher levels of N even though it was shown to reduce longevity. If bee life cycles are shortened, it reduces the window in which they can overlap with their host plants. Understanding how the interaction of climate change drivers impacts ecological relationships is thus very important. 

Pesticides Found to Increase Bee Susceptibility to Colony Collapse Disorder

Since becoming common place in the mid 1980s, scientists have identified over sixty factors contributing to colony collapse disorder (CCD). This disease has the capacity to quickly decimate honey bee populations and posses a significant ecological and economic impact to the United States. Wu et al. tested the impact of common pesticides on worker honey bees (Apis mellifera) by raising three cycles of the species in combs treated with pesticide residue. The results demonstrated a number of sub-lethal effects to colonies such as reduced longevity, delays in the life cycle process such as larval development and adult emergence. These sub-lethal effects leave honey bee colonies more susceptible to pathogen infections which are known to cause colony collapse disorder.
Wu, J., Anelli, C., Sheppard, W., 2011. Sub-lethal effects of pesticide residue in brood comb on worker honey bee (Apis mellifera) development and longevity. PLoS One 6.

            Wu et al. used a relatively straightforward experimental design to test for the effects of pesticide in brood comb on worker honey bees. Using three colonies of similar strength from the USDA honey bee laboratory, researchers set up frames with a low pesticide residue control comb paired with a comb with high pesticide residue. For each pair of combs, queens were given access to both during a 24 hour period of egg laying. After eggs were laid, the combs were photographically monitored in patches to determine larval mortality on days 4, 8, 12, and 19. Beginning on day 19, both the control and test combs were incubated at 33°C and the emergence of adult bees was recorded as accounted-for adults were tagged with Testor’s enamel. After three generational cycles, the combs were sent to a lab to have their pesticide levels determined through spectrometry.
            While there was no statistical difference in larval mortality between the test and control broods, Wu et al. found delayed development at days 4 and 8 in the test combs. The lack of differential mortality rates in the larval stage may be due to cross-contamination of the control broods by bees from the infected comb. This seems especially plausible given that larval mortality increased in the control combs in the second and third generations. A chemical analysis of the control combs found that many pesticides from the test combs were present after the experiment, suggesting these chemicals can spread quickly to non-infected bee populations. In terms of adult emergence and longevity, Wu et al. found an average delay of about two days in adult emergence in test populations. In the control populations, there was a delay in adult emergence in the second and third cycles, suggesting that the impact of traveling pesticides. Furthermore, the results showed that bees from comb without pesticides lived an average of four days longer than the bees from the test populations.
            The results of Wu et al. point to pesticides as being responsible for sub-lethal effects on bee populations which can increase susceptibility to pathogens responsible for CCD. A drawn out life cycle provides a reproductive advantage for Varroa mites which feed on the hemolymph of pupating bees. The longer honey bees remain in a larval stage, the higher the level of mite reproduction, posing a serious threat to colony health. Furthermore, the researchers argue that the early death of adult worker bees in colonies with pesticide in the combs can lead to foraging and other responsibilities taken on by younger bees which negatively impact the overall health of the colonies. While further research is required, Wu et al. argue exposure to pesticide seems to be another plausible cause of colony collapse disorder. The paper argues that bee keepers should end the practice of reusing wax which can build up high levels of pesticides over a relatively short period of time. 

Toward a Greater Understanding of Wild Bee Phenological Advances and the Dangers of Climate Change

Given that climate change has been linked to phenological advances in numerous species of flora and fauna worldwide, new research is being done to determine what, if any, unique challenges mutualistic ecological relationships face as global temperatures continue to rise. Bartomeus et al. (2011) seek to determine to what extent wild bees of northeastern North America have undergone phenological advances due to climate warming and whether their host plants have are advancing in compatible ways. Researchers found wild bee phenology to have advanced in the last few decades paralleling global warming. However, they also determined that the the ten species of bees studied have kept pace with the phenological advances of their host-plants in the region. Nevertheless, further research must be done to determine if climate change will eventually cause phenological mismatches between bees and their host-plants.
Bartomeus, I., Ascher, J., Wagner, D., Danforth, B., Colla, S., Kornbluth, S., Winfree, R. 2011. Climate-associated phenological advances in bee pollinators and bee-pollinated plants. PNAS 51.

            Phenological advances have been recorded in many plant and animal species over the last fifty years as a result of climate warming. One potential threat to food production caused by phenological advance is what is known as a phenological ‘mismatch,’ when a mutualistic relationship in an ecosystem is destroyed because the species in question undergo different advances as temperatures increase. Generalist species of wild bees are a critical pollinators in North America yet until Bartomeus et al. no major study had been launched to determine phenological advances in key species. Using historical data from museums over a 130 year period for ten species of wild northeastern North American bees, researches sought to determine phenological advance by comparing the day in April over time bees were sited with the historical mean temperatures for the month over the time period studies. The results demonstrate a mean advance for the ten species between 10.4 and 1.3 days in April.
            There were many challenges in the formulation of this study and the collection of data. Unlike many other fauna in North America, there exists no standardized scheme for monitoring bees, thus researchers had to collate data from a variety of institutions collected in disparate ways. The ten species chosen for the study were selected for the richness of data and for the widespread presence of all ten species in the geographic area being studied. Furthermore, Bartomeus et al. argue little is known about the relationship between bee development and environmental triggers, with the few studies completed thus far showing North American bees to have complex relationships to winter and spring temperature changes. Finally, despite the results shown by this research project, the authors argue for the need of more complex, physiological models to predict phenological advances in bees and their host-plants into the future, beyond the data confines of this paper.
            Having graphed historical data on collection days in April for the ten bee species in question and mean April temperatures against the year of collection, Bartomeus et al. demonstrate that the bees in question have been appearing earlier and earlier as temperatures increase. Roughly 69% of phenological advance has occurred since 1970, mirroring the comparatively steeper increase in mean temperatures since that time. This data leads researchers to conclude phonological advance appears to be gaining in severity as average temperatures increase. To see if there was threat of a mismatch between the bees and their host-plants, Bartomeus et al. used four published studies on   phenological advance in native plant species in the region under analysis which flower during the period in which the bees are active. In two of the studies, the researchers found bees to be advancing faster than host-plants by 3% to 33%, however the other two studies suggest there is no clear pattern of divergence. To further complicate these mixed results, the authors argue not enough data exists to determine whether the demonstrated divergence is a result of actual biological differences or simply methodological error. Thus, further research is needed to gain a clearer insight into threats of phenological mismatch in natural pollinators in North America.

Climate Change to Threaten Bee Populations in the Cape Floristic Region of Southern Africa

Bees are a critical pollinator in global food systems and thus a keystone species in the maintenance of healthy ecosystems. The Cape Floristic Region of South Africa enjoys a high level of ecological diversity however in the last five years multiple studies have demonstrated statistically significant increases in mean daily temperatures in both its winter and summer rainfall areas. The threats climate change pose to both generalized and specialized bee species have begun to be documented in Europe however, despite their importance, no similar research has been done into South African bee populations. Changes in temperature and meteorological conditions could have a negative impact on bee species’ ranges and population numbers in the coming century. Kuhlmann et al. (2012) thus seek to determine what effect, if any, climate change will have on twelve major ground dwelling bee species in the Cape Floristic Region (CFR) of South Africa. The researchers compared current and historical bee population data for the twelve species with future climate projections in the region based off the WorldClim Data Base and the 2006 Land Cover Project. Kuhlmann et al. (2012) found climate change to threaten bee ranges across the board with greater risks to winter rainfall species.

Kuhlmann, M., Guo, Danni., VEldtman, R., Donaldson, J., 2012 Consequences of warming up a hotspot: species range shifts within a centre of bee diversity. Diversity and Distributions, 2012.

Kuhlmann et al. (2012) chose for their study twelve ground-dwelling bee species from the CFR due to the comparatively significant distribution records available for them, their occurrence in both the winter and summer rainfall areas, as well as their overall importance as pollinators. Historical bee records from museums and natural records were collected irrespective of date, however a vast majority of available data dates from after 1980. Kuhlmann et al. used the program MaxEnt to model potential future geographic ranges for the twelve bee species. This program was selected because it can make up for relative small sample sizes by comparing input data with larger systematic ecological surveys. The MaxEnt projections were compared to the results of the HadCM3, or the Hadley Centre Climate Model, a climate projection model which is favored by scientists studying the CFR. Kuhlmann et al. modeled two scenarios for climate change by 2080, one in which the CFR had a high increase in population and CO2 emissions, and a second in which a commitment to environmental preservation prevents population and emission increase. The researchers chose a number of climatic and environmental variables in their projections with a focus on seasonality in rainfall, which is a critical factor in bee ranges.

Regardless of the climate scenario used, the results of Kuhlmann et al. suggests thatclimate change will have a major impact on the geographic ranges of all twelve bee species studied. If seasonal rainfall rates are impacted as these results suggest, eight of the twelve species of bees will see a net reduction of possible geographic range with five species seeing dangerously dramatic decreases. While changes to the species of the summer rainfall region are marked by shifts in geographic ranges, species of the winter rainfall species face reduction in overall geographic ranges, thus making them markedly more vulnerable to climate change in the region. Previous studies have suggested that the summer rainfall species have the capacity to travel east in the CFR to more favorable climate ranges in the future. However, for some species such as Patellapis, which are primitively social at higher temperatures and serves as major pollinators in the region, may become more abundant as winters warm over the coming decade.

Given that this is the first study of its kind in the CFR, Kuhlmann et al. are careful to ground their results with a call for further research. Of particular importance for researchers of pollinators and climate change is the issue of plant-pollinator interaction. The bee species studied in this article show little to no synchronization with their host plants, leading to the hypothesis that even if bees are able to migrate in the CFR, if their host plants are negatively impacted by climate change it could be enough to decimate these bee populations. Kuhlmann et al. argue for establishing population monitoring facilities in the coastal lowlands of the CFR for further study of the winter rainfall species which are believed to be especially at risk from climate warming.

Climate Change Poses Risk to European Bee Populations

Bees perform a critical role as pollinators in the ecosystems humans depend upon for food. Unfortunately, climate change poses significant risks to the habitats of important organic elements of the food cycle such as bees. Given the prevalence of Colony Collapse Disorder and various vectors and pathogens already ravishing Europe’s continental bee populations, Roberts et al. (2012) seeks to assess extinction threats to six species of pollinating bees by projecting climatic changes across Europe through 2050. By modeling temperature changes and growth rates of key plant species, the researchers hope to better understand where, if anywhere on the continent, these bee species will be able to survive. This is the largest geographic area ever studied for an experiment of this kind; the continental scope allows researchers to compare local and distant climatic changes which they believe will assist in predicting migration patterns for threatened bee species. The study found significant risks posed by climate change in the coming decades to all six bee species researched.
Roberts, Stuart P.M., Potts, Simon., Biesmeijer, Koos., Kuhlmann, Michael., Kunin, Bill., Ohlemüller, Ralf., 2011. Assessing continental-scale risks for generalist and specialist pollinating bee species under climate change. BioRisk 6 118.

            Roberts et al. selected six well-dispersed bee species in Europe, three of which were generalist species, meaning that they pollinate many different plants, and three of which were specialist species, meaning that they only forage for a specific plant. The researchers took 125 years of distribution data for the six bee species and organized it on a presence/absence map of Europe made up of 10’ grid cells. They also gathered distribution data for the chosen plants of the specialized species as well as records of climatic conditions from the past fifty years and predictions for the next fifty. Combining these data, Roberts et al. were able to create bioclimate models which determined the preferred climates of the six species in question. When they tested the model in present conditions, its results overlapped closely with the actual bee populations. By 2050, the model predictions showed all six species suffering severely curtailed local and continental suitable habitats. One species, C. impunctactus, was predicted to have little to no suitable climate in all of continental Europe by 2050.
            An interesting component of this project was the testing of both generalist and specialist species of bee. Given that the specialist forage plants are widely distributed across the continent, Roberts et al. conclude threats to bees are not related to specialization. Rather, the major common threat to all six species is a severe reduction in climatically suitable ranges and growing isolation between these shrunken ranges. Most dramatically, the aforementioned C. impunctatus would have to travel over 100 km to find any climatic region in which they could conceivable live. For the specialist species C. Wolfi, 70% of regions local to its current location will become uninhabitable, however most of Europe will remain habitable if the species manages to disperse. In the best case, the model predicts two of the specialist species, C. anchusae and C. hederae should have significant local and continental habitats still suitable by 2050. Even though the latter two species might fair better, all six face increased isolation which could negatively impact rates of pollination.
            While Roberts et al. argue that greater research is required to generate a fuller understanding of climate change on pollination, they do offer a few conclusions from their research into six species of bee. They demonstrate the strong likelihood that decreased populations and increased isolation will become more common as temperatures raise through 2050. It seems logical to suggest that many more of Europe’s 2,250 species of bee could also be at risk from climate change. One possible consequence of a decline in suitable climatic regions could be the spread of parasites as colonies are forced to migrate. Two of the species studied are believed to be transmitters of parasites. A spread of vectors could significantly decrease the already dwindling bee populations, even in areas with suitable climates. 

Study Finds North American Bumble Bee Populations Dangerously Low, Prone to Infection

Healthy bumble bee (Bombus) populations are essential to the pollination of commercial agriculture and wild plant communities in the United States. Unfortunately, initial studies confirmed the widespread fear that American bee numbers were drastically shrinking. Cameron et al. (2011) make important progress in understanding the reasons behind the dwindling number of bumble bees through a three year interdisciplinary research project tracking distribution patterns, genetic diversity and pathogen infection levels in bumble bee populations in each major bee region of the United States. Their research confirms that the presence of four major species has declined by up to 96% while their geographic presence has shrunk 23–87% over the last two decades. Furthermore, declining populations are distinguished by the presence of the pathogen Nosemba bombi and low levels of geographic diversity. While the research provides pathogen levels and genetic diversity as predictors for population collapse, the cause remains unknown.–Michael Landsman

Cameron, S., Lozier, J., Strange, J,. Koch, J., Cordes, N., Solter, L., Griswold, T. 2011. Patterns of decline in North American bumble bees. PNAS 108, 66–-667.

American food production has become dependent upon bumble bees for pollination since recent domestication in major agricultural areas. Their comparatively large anatomy, long tongues and high frequency buzzing, which helps scatter pollen off their bodies, make them uniquely efficient pollinators. Recently North America has joined other global regions in witnessing disturbingly fast-paced bee population decline. Various hypotheses speculating on the causes of bee decline have been made yet Cameron et al. (2011) represents the first major study into the problem in North America. This study sought to accomplish two major tasks; to quantitatively demonstrate a reduction in bumble bee populations and geographic ranges, as well as to test for two of the projected reasons for population decline, pathogens and genetic diversity levels. To quantify current population and geographical ranges, the team chose four varieties of the bumble bee in North America and compared empirical data from the last two decades with a count taken between 2007 and 2009 at over three hundred locations in North America. To determine pathogen infection rates and genetic diversity, the project examined midgut tissue samples of over six thousand bumble bees from representative regions and performed genotypes on both stable and declining populations. Their findings demonstrate both an overall reduction in bumble bee population numbers and geographic ranges and that communities which have suffered the most feature low levels of genetic diversity and a prevalence of the pathogen Nosemba Bombi.

Many followers of bee decline in Europe have blamed the rising temperatures and diminished food sources resulting from climate change for the drastic drop in numbers. Cameron et al. (2011) have observed that in North America, even species which have previously withstood wide climactic variations are facing population collapse, thus they argue for the inclusion of other elements in exploring the root of the bee problem. While the widespread tissue study highlighted the prevalence of N. bombi in declining populations, the authors do not assert their study yielded sufficient evidence to argue the pathogen is a cause of decline; future research is required to determine whether or not N. bombi becomes a hallmark of populations already in decline. While bumble bees can pick up certain infectious pathogens from contact with flowers, no tests have yet explored whether N. bombi is transmitted this way. While the presence of N. bombi is a useful warning sign for threatened bee populations, there remains much more research to do in understanding the infectious agent’s exact role.

An exploration of genetic diversity in bumble bees through genotyping confirms initial suspicions that populations in decline suffered from smaller gene diversity. In a situation similar to that of the N. bombi question, further research needs to be done to determine whether small gene pools is a cause or effect of species dwindling. The genotype study found significant gene flow among populations across a very wide scale. While this is good news in the sense that there is a possibility for dwindling communities to diversify, it also means infectious contagions have the ability to travel long distances as well. The authors expect more research to be done in this area before definitive statements on the cause of this bee crisis. With regards to climate change, it would be useful to determine if limited gene diversity makes bumble bees more vulnerable to temperature variance. Hopefully a major study in PNAS and the dangerous threat to food production dwindling bumble bee numbers present will provoke further research in the area.