August 10, 2016 at 3:53 pm by Kalyn Bickerman-Martens
“Can you tell how old a bee is?”
This is a question that I frequently hear when people ask about my bumble bee research. This goes hand in hand with another question: “How long do bees live?” As an ecologist, I study how bumble bees relate to one another and their environment. Being able to determine the “age” of my study bees is important. It’s an integral piece of information I collect on each bee, along with forage plant, location, sex, and species.
The short answer about bumble bee lifespan is that it varies quite a lot depending on species, environmental factors, and whether the bee is a queen, male, or worker. Queens have the longest lifespan. In the fall, newly emerged queens go underground for the winter months and then re-emerge in spring to find nest sites, lay eggs and establish colonies. Once their worker daughters take over foraging duties, queens remain in their nests and continue to lay eggs through the growing season. But when fall arrives and hard frosts turn summer flowers brown, all of the colony members die – including the old queens. The exceptions are the new queens who have already gone into hibernation. Therefore, if a queen survives the winter and is successful in founding a colony the next spring, she will live a full year.
Male bumble bees are produced in the colonies from mid to late summer. Newly emerged males spend a few days in the nest consuming food stores without contributing to the workload. After this time, they leave and do not return. They spend their time feeding on nectar and attempting to locate new queens for mating. Unlike males of most other social insects, which typically die soon after mating, male bumble bees are thought to live several weeks.
Most of the research on bumble bee lifespan has been done on the female workers, who are responsible for gathering nectar and pollen and defending the nest. There is no definitive estimate, but their life expectancy ranges from just a couple of weeks in the field to over a month when kept in the lab. Foraging is a dangerous activity, which puts workers at a high risk of predation (e.g., by birds, dragonflies, and spiders) and exposure to severe weather like heavy rain, high winds, and extreme temperatures. It’s also possible that total “work effort” and energy expended are linked to total life span, and that the “hard work = early death” hypothesis may be a driving factor in limiting the lifespan of worker bees. Therefore, keeping a bee in a laboratory setting where there is no predation risk and no need to forage would prolong its life.
Now that we’ve answered the question about how long do bumble bees live, what about telling how old a bee is? Multiple papers have found that bees’ wings degenerate with use and that there is a link between the amount of degeneration and a bee’s age. Through time and use, bees’ wings will become frayed and torn. This increases the wing-loading, which is the relationship between the weight of the bee to the total area of its wings (milligrams per square millimeter). As wing wear increases, the wing-loading measurement increases, which translates to a higher energy cost for the bee. Torn and tattered wings also limit maneuverability, which can increase a bee’s risk of predation.
In my research, I use a four-point scale from 0 – 3 to “age” my study bees.
0 = perfect wing with intact margin
1 = a couple of nicks, no major wear or tear
2 = wing margin nearly completely tattered
3 = wing margin gone, with large chunks missing
Although the degree of wing wear cannot be directly correlated with a bee’s age in days or weeks, a score of “0” likely represents a very young bee. Likewise, a score of “3” could indicate an older bee nearing the end of its lifespan. As in butterflies, moths, dragonflies, and other insects that spend a lot of time flying, we know there is a positive relationship between wing wear and a bees age. The relationship is not exact however, probably because of environmental variation.
Interestingly, a 1987 paper concluded that there may be a latitudinal effect on bumble bee lifespan with bees in higher latitudes having shorter lifespans. Previous studies noted that foraging bumble bees in Brazil (Bombus morio) had an average lifespan of 36.4 days whereas bees in New Brunswick (Bombus terricola) only lived 13.2 days. One hypothesis for this is that longer days in the summer months mean more time per day spent foraging, resulting in more energy expended per day. Also, cooler temperatures at higher latitudes mean more energy is required to maintain suitable temperatures in the nest. Finally, if bees are forced to fly farther in order to locate floral resources, this can also result in shorter lifespans (hard work = early death) (Goldblatt & Fell 1987).
How does bumble bee lifespan compare to that of other social insects? Some worker ants can live up to several years and queen ants of the harvester ant species Pogonomyrmex owyheei can live as long as 30 years! Honey bee workers most likely have similar lifespans to bumble bees in the summer but can live inside the hive for up to a few months during the winter, whereas honey bee queens can potentially live five years or more.
Cartar, R. V. 1992. Morphological senescence and longevity : an experiment relating wing wear and life span in foraging wild bumble bees. Journal of Animal Ecology 61:225–231.
Goldblatt, J., and R. Fell. 1987. Adult longevity of workers of the bumble bees Bombus fervidus (F.) and Bombus pennsylvanicus (De Geer) (Hymenoptera: Apidae). Canadian Journal of Zoology 65:2349–2353.
Mueller, U. G., and B. Wolf-mueller. 1993. A Method for Estimating the Age of Bees : Age- Dependent Wing Wear and Coloration in the Wool- Carder Bee Anthidium manicatum ( Hymenoptera : Megachilidae ). Journal of Insect Behavior 6:529–537.
January 25, 2016 at 6:34 pm by Kalyn Bickerman-Martens
As I write this on a cold January morning with snow falling outside my office window, the mated bumble bee queens that emerged last fall as their parent colonies were ending are now hibernating under the soil waiting for spring. Their bodies are able to produce glycerol, the same ingredient in anti-freeze, which keeps them from freezing completely. Technically, the queens are in a state called diapause, during which their metabolisms have slowed as they consume the fat and nectar reserves they collected in the fall. This stage will last for six to nine months depending on location. Temperature and day length are thought to potentially control the onset and termination of diapause.
We have had unusual weather for the Northeast in the past few months as a particularly strong El Niño event has affected our climate. El Niño (“little boy” in Spanish) is a large-scale ocean-atmosphere climate interaction linked to warming sea surface temperatures in the Pacific Ocean near the equator. Occurring on average every two to seven years, an El Niño creates a very active jet stream across the southern US which keeps much of the cold air in Canada. This results in warmer-than-average temperatures for the Northeast and colder-than-average temperatures across southern states. This past fall, Maine experienced one of the strongest El Niño events since the late 1990s, with temperatures well above normal. The National Weather Service reported temperatures in northern and eastern Maine averaging 1.5 to 4 degrees Fahrenheit above normal, and we saw Bangor tie its previous Christmas Day record of 54º F, well above the 31º F average and Portland reach 62º F, leaving the old record of 54º F in the dust.
Will these unusually warm fall and winter temperatures have an effect on the metabolism of bumble bee queens in diapause? The rate of all biological mechanisms increases with temperature, especially in animals whose internal temperatures vary with external temperatures, such as insects. Because the queens’ metabolisms will be processing at a faster rate, they may consume more of their fat and nectar stores during warmer temperatures. This could potentially result in a depletion of resources such that a queen might not survive until spring.
Another possible effect of a warm winter is that important early season sources of pollen and nectar, such as willows and rhododendrons, may bloom earlier than usual. Bumble bee queens may emerge after the high point of this bloom, resulting in less availability of these resources, which are often staples for the establishment of new colonies. Indeed, the National Weather Service Climate Prediction Center does predict that temperatures in April – June of this year will be above normal.
The bottom line is that we cannot be certain as to how the 2015-2016 El Niño will affect our bumble bee populations for 2016. An important thing to keep in mind is that bumble bee population dynamics are not static from year to year. The relative abundances of bumble bee species can vary each year with weather and climate conditions and complicated interactions between species and resources occur with these changes. Some bumble bee species do tend to be more tolerant of a wider range of climates, such as the broadly dispersed Eastern Bumble Bee (Bombus impatiens), and may have a competitive advantage in times of climate uncertainty.
For more information:
Fall 2015 Climate Summary for northern and eastern Maine. Available from http://www.weather.gov/car/Fall2015ClimateSummary
Three Month Outlooks. Available from http://www.cpc.ncep.noaa.gov/products/predictions/long_range/seasonal.php?lead=4.
What are El Niño and La Niña? Available from http://oceanservice.noaa.gov/facts/ninonina.html.
Map Image obtained using Climate Reanalyzer (http://cci-reanalyzer.org), Climate Change Institute, University of Maine, USA.
October 30, 2015 at 1:06 pm by Kalyn Bickerman-Martens
With Halloween just a day away, who wouldn’t love a good ghost story to liven up our favorite spooky holiday?! But this ghost story is a true tale – about a once common species in the midst of a very scary vanishing act. Named for the distinctive orange-brown patch on its abdomen, the Rusty-patched Bumble Bee (Bombus affinis) was once a common sight throughout its range, which extended across the eastern United States from Maine south through Georgia and west to Minnesota and southern Canada. But since the late 1990s, this species has undergone an alarming population crash. Today, its numbers have declined by an estimated 95% and its geographic range has shrunk by 87%. To find a Rusty-patched Bumble Bee anywhere today would be like looking for a ghost!
The specific cause of this decline is unknown, but there are some plausible theories at the front of the line. All bumble bees in the United States face similar threats: widespread use of pesticides; introduced parasites and diseases spread through the use of commercially-raised bumble bees; habitat loss and fragmentation; and in some cases, climate change. The Rusty-patched is not the only bumble bee that is disappearing from the North American landscape. At least three other species have experienced similar rangewide declines, including another Maine native – the Yellow-banded Bumble Bee (Bombus terricola). But not all of the continent’s 46 bumble bee species are in trouble. Some are even expanding their range and increasing in abundance compared to historical data. So why are some species vanishing while others seem to be doing just fine? One explanation may be genetics. Interestingly, three of the four species undergoing severe declines, including the Rusty-patched, are closely related to each other. Perhaps they share the same susceptibilities to threats that other species are more tolerant of?
This past year, the International Union for Conservation of Nature classified the Rusty-patched Bumble Bee as “Critically Endangered” (extremely high risk of extinction in the wild). Just last month, the U.S. Fish & Wildlife Service announced it is initiating a status review to determine if the species qualifies for listing under the federal Endangered Species Act. With the exception of a few isolated populations in the Upper Midwest and southern Ontario, where individuals are rarely observed, this once abundant and widespread pollinator now appears to have vanished from most of its former range. But what about Maine – could it still be here, hiding like a ghost in isolated corners of the state?
The last credible record of a Rusty-patched Bumble Bee in Maine was in 2009. Despite continued searching in the same area, it has not been seen again. But if there is any hope of finding it, it will likely be in the next few years. The Maine Bumble Bee Atlas (MBBA) project, which got underway this past spring, is unleashing a small army of citizen scientists to survey Maine’s bumble bee fauna over the next five years. Maybe we’ll get lucky, like they did in Virginia last year when ONE Rusty-patched Bumble Bee was found amongst 35,000 bees collected during an intensive sampling effort. And there is some good news that could herald a possible discovery of our own hidden population of Rusty-patched Bumble Bees. While still in decline in other parts of its range, the Yellow-banded Bumble Bee appears to be making a comeback in Maine and the Northeast! Last year it was present at nearly half of the field sites sampled by the University of Maine and this year it is turning up in most of the MBBA collections from across the state. If its sister species can develop resilience to and bounce back from the threats that sent them both into rapid decline, and if it’s not too late, the Rusty-patched Bumble Bee might just have a chance for a similar recovery and once again haunt the Maine landscape.
For more information about the Rusty-patched Bumble Bee:
The Xerces Society: http://www.xerces.org/rusty-patched-bumble-bee/
COSEWIC Assessment and Status Report: http://www.sararegistry.gc.ca/virtual_sara/files/cosewic/sr_Rusty%20patched%20Bumble%20Bee_0810_e.pdf
The IUCN Red List of Threatened Species: http://www.iucnredlist.org/details/full/44937399/0
For more information about the Maine Bumble Bee Atlas:
September 23, 2015 at 5:54 pm by Kalyn Bickerman-Martens
A question that tends to come up when discussing bumble bees (and honey bees) is: “Aren’t they all female?” The answer is that YES, most of the bees we see during the summer, such as the queens and the workers that do the foraging, are female. However, bumble bees still need males to contribute genetic material to the next generation – colonies that will be founded by new queens the following year. Now that it’s officially fall, I’ve been seeing quite a few males and even some new queens on my collecting trips, indicating that the colonies have entered “the beginning of the end” of their colony cycles.
A bit of genetic background: a chromosome is a package inside of an organism that contains that individual’s DNA and is passed from parent to offspring. Humans have 23 pairs of chromosomes and one copy of each chromosome is inherited from the female parent and the other is from the male parent. These chromosomes contain all the genetic hereditary information. Because there are 23 pairs, this means humans have 46 total chromosomes within each cell. Because our chromosomes come in pairs, humans are diploid.
Bumble bees (and other members of the order Hymenoptera) have a “haplodiploid” sex-determination system. This means that females are diploid (have two sets of chromosomes) whereas males are haploid and only have one set of chromosomes. How does this happen? Workers (and future queens) develop from fertilized eggs which contain genetic material from both the queen and the male drone with whom the queen mated the previous fall. Males, on the other hand, develop from unfertilized eggs and all of their genetic material is 100% from the queen. Technically, workers are also capable of laying eggs that would develop into males, but the queen uses a pheromone (an excreted chemical factor) to inhibit worker ovary development since it is in the queen’s genetic interest that all of the offspring in the colony are her own.
In the beginning of the colony cycle, the queen lays only fertilized eggs that turn into worker females. It is only toward the end of the season when she begins to lay both unfertilized eggs that turn into males and fertilized eggs that will develop into the new queens. The factors that cause the fertilized eggs to turn into new queens instead of more workers are not fully understood, and could differ between species. However, research suggests that queen larvae in some species may be fed more frequently as compared to worker larvae. Another possible reason is that worker larvae may be exposed to the queen pheromone very early in their development, which acts to suppress their ovary development.
It has been suggested that the density of workers in the colony is what triggers this switch to laying reproductive males and queens, since there needs to be enough workers to feed the larval queens, which require more food and take longer to develop than workers. The new queens do leave the nest during the day to forage and return at night, but usually do not contribute to provisioning the colony. At this point their main priority is building up enough fat reserves for the long winter ahead. Males, on the other hand, leave the colony and focus on finding a new queen from another colony with whom to mate, often by dropping pheromones in an area then patrolling until queens arrive.
Once males and the new queens depart the nest, the colony has reached its end for the season and the remaining workers and founding queen die. This entire cycle will be repeated once the new queens emerge from their winter dormancy the following spring.
Chromosomes. 2015. Available from www.genome.gov/26524120 (accessed September 1, 2015).
Goulson, D. 2010. Bumblebees: behaviour, ecology, and conservation, 2nd edition. Oxford University Press, New York, NY.
Haplodiploidy and relatedness in bumblebees. 2015. Available from www. bumblebee.org/Haplodiploidy.htm (accessed September 1, 2015).
September 10, 2015 at 6:17 pm by Beth Swartz
We are pleased to announce that in addition to a website and Facebook page, we now have a blog dedicated solely to the Maine Bumble Bee Atlas (MBBA) project! MBBA is a five-year (2015-2019) statewide survey of Maine’s bumble bee fauna coordinated by the Maine Department of Inland Fisheries & Wildlife (MDIFW) in partnership with the University of Maine at Orono and Farmington. Closely modeled after MDIFW’s highly successful Maine Butterfly Survey (2007–2015) and Maine Damselfly and Dragonfly Survey (1999-2005), MBBA engages volunteer citizen scientists from around the state to help survey and document the diversity, distribution, abundance and habitat use of bumble bee species in Maine.
The blog will serve as a place to communicate information and updates about survey results and the project’s progress to both volunteers and the general public. During MBBA’s first field season, over 100 volunteers were trained in the project’s survey and data collection protocols. This enthusiastic group of citizen scientists has been out in the field all summer collecting data on Maine’s bumble bees and will soon be sending their data back to MBBA – so stay tuned, we’re expecting some exciting results! We’ll also use the blog to share interesting news and information about the life history, ecology and conservation of bumble bees. We encourage you to participate and envision the MBBA blog as an opportunity for folks to share their bumble bee experiences as well!