August G. Beckemeier Conservation Area – A Thousand Acres of Silphiums

Photographic Observations of a Communal Nesting Sweat Bee (Agapostemon virescens)

Hymenoptera, insects, macro, wildlife, wildlife photography

For the past few years I have noticed a good number of native bee nest holes along exposed sections of bare soil at one of my favorite hiking and nature observation sites – August G. Beckemeier Conservation Area in St. Louis Co., MO. This past spring I finally decided to make this a project and set about a quest to make some images of these gals provisioning their nests. As usual, I wound up learning along the way.

An *Agapostemon virescens* pauses at the entrance of the largest of the communal nest entrances I observed. It is impossible for me to accurately count the number of females using this ~ 10 cm tall conical entrance, but I observed six individuals at one time on or hovering above the entrance.

As is commonly known, many of our native bees are solitary and nest without close contact or cooperation in regards to conspecifics. At the opposite side of this spectrum of sociality in the Hymenoptera are most species of bumble bees and the honeybee. These bees are considered truly social, or, eusocial. The characteristics necessary to be considered a eusocial species are 1) cooperative care of offspring of others within the colony, 2) overlapping generations within a colony of adults, and 3) a division of labor into reproductive and non-reproductive groups. Many of our bee species lie somewhere between these two extremes. The bee of focus here, Agapostemon virescens, lies early in the area we call being presocial, aka parasocial.

Two *Agapostemon virescens* females exiting a communal nest entrance having dropped off their loads into their individual cells.

Let’s clarify the differences between a presocial species such as A. virescens and the eusocial honeybee. The honeybee shows all three necessary characteristics of a eusocial species. The individual workers obviously care for brood that are not their own – they don’t even have offspring of their own, instead spending much of their lives caring for the offspring of their queen (sisters). They have multiple overlapping generations within the hive in a particular season, as well as across multiple seasons and as just mentioned, there is a division of labor into reproductive and non-reproductive castes. A. virescens on the other hand, is not nearly as cooperative. Individuals of this species share basically just a front door to their brood chambers and nothing more. After entering the communal nest, each female builds their own brood sub-chamber cells and each provisions their own by processing pollen into cakes and leaving them in their respective brood chambers. There is no brood care after the egg is deposited and the sub-chamber sealed. The offspring then emerges later in the summer.

So, what are the pre-conditions necessary for the eventual development of more complicated forms of sociality, i.e. eusociality? Or more directly, what advantages are there in adopting more of a social lifestyle if we assume the starting point was a solitary existence? Scientists consider two important pre-conditions need be met for the evolution of eusociality. First, the species offspring must be altricial, or require a great amount of parental care in order to reach maturity. Second, there need be low reproductive success rates of solitary pairs that attempt to reproduce. Here is what is believed to be the primary driver that pushed A. virescens into this presocial condition.

A sentry Agapostemon virescens stands guard at the communal nest entrance allowing only conspecifics to enter. This guarding of potential kleptoparastism is regarded as the primary benefit that led to communal nesting in this species.

This sentry *Agapostemon virescens* closely inspects an incoming conspecific. How it is determined who stands watch while its neighbors forage is not known.

Kleptoparasitism is where one animal takes advantage of the hard work of another by taking their prey or collected foods. In this case, we are primarily concerned with the large group of bees known as cuckoo bees. Kleptoparasitism has evolved numerous times in the Hymenoptera and cuckoo bees lay their egg on or near the host’s provisions. The parasite will hatch first and eat the host’s pollen and will often kill and eat the host’s larvae as well. With such an obviously successful reproductive strategy, it should come as no surprise that there would be a strong selective advantage of finding ways to thwart these parasites. In the case of A. virescens, evidence suggests that by communal living as described here, the rate of kleptoparasitism is much lower when compared to related species that have the completely solitary reproductive strategy.

A busy day of bringing in pollen provisions for these *Agapostemon virescens* sweat bees.

I guess the obvious next question is how in the world could eusociality evolve from this state? This is a fascinating story that involves terms like kin selection, altruism and haplodiploidy. It also involves a good deal of math and explanation from some of the greatest evolutionary thinkers since the time of Darwin (read anything by William D. Hamilton for example). It is also well out of the scope of this piece. But, I hope it is clear that before getting near the high rung of eusociality on this ladder, that a small first step like seen in this example would be necessary.

Although *Agapostemon virescens* sweat bees are communal nesters, this photo gives a clue that they are not cooperative foragers like the honeybee. Each of the three returning females is carrying different colored pollen, indicating different pollen source plants for each.

I hope I got most of this correct enough. It’s been a long time since I took Zuleyma Tang-Martinez’s Evolution of Animal Sociality class at University, which I thoroughly enjoyed. Please feel free to leave a comment to correct or clarify or ask a question.

Much of what I covered here and a lot more can be found in Malte Andersson’s The evolution of eusociality (Ann. Rev. Ecol. Syst. 1984. 15:165-89

The evolution of Eusociality

Spring Beauty Rust (Puccina mariae-wilsoniae)

fungi, macro, native plants

I shared some images and info on the spring beauty rust last year. I did not find it nearly as prevalent this year in the same patch of spring beauty (Claytonia virginica) but I was able to find the alternate and rarer sporulating telia. The life cycle of the Puccina rusts are very complex and often require the use of two hosts (heteroecious). In the case of this species, there does not seem the need to use more than one host to complete its lifecycle. The first sporulating legions are the yellow “cluster cups” or aecia. These structures burst open and release dikaryotic (containing two nuclei) aeciospores.

“Cluster cups” or aecia of *Puccina mariae-wilsoniae*

The next photo shows the darker teliospore-producing telia. Known as “black rust” in the wheat pathogen, the teliospores are able to survive harsher conditions in the environment and do not need the strict temperature and humidity requirements to survive and infect the next generation.

This is all I have for now. Next year I would like to see if I can get photographs of each respective spore if I can figure out the right equipment.

-OZB

The interesting and important Spring Beauty (Claytonia virginica)

Hymenoptera, insects, macro, native plants

Until this spring, I assumed that spring ephemerals, like Claytonia virginica (spring beauty) and others that begin flowering in early spring, did not provide much sustenance for early season pollinators. For no reason in particular, I assumed that most of these plants preferred selfing versus providing the resources to attract insect pollinators.

After taking a closer look at the blankets of C. virginica that lie on the slopes of Beckemeier Conservation Area near our house, my eyes were opened. I found pollinators everywhere on multiple trips during this long and cool spring. Unfortunately many species were so quick that they eluded me and my camera. However, I managed to nab a few of the more cooperative and with some help of those smart folks at BugGuide.Net, I got as close to the right identifications as I could.

Andrena erigenidae, the spring beauty bee

Have you heard of oligolecty? Until doing this research, I had not either. Oligolectic is a term that describes certain bees species that have specialized preference to pollen from only specific plant groups – plants from a small group of genera, a single genus, or in this case, one single species.

*Andrena erigenidae* reaching for its nectar reward

The spring beauty bee (Andrena erigenidae) is a mining bee (Andrenidae) that feeds exclusively on the pollen and nectar of C. virginica. In fact, the larvae of this species cannot grow optimally on any other pollen source. So, it may not come as a surprise that this was the most common bee I found foraging on the fields of spring beauty.

*Andrena erigenidae* female with pollen-laden legs

These mining bees will take the pollen during a flight run that may last up to more than an hour and then bring it back to their self-constructed nursery hole in the ground. There they will turn the pollen into cakes and lay a single egg on each. This will be all the material needed for an individual larvae to develop into an adult.

*Andrena erigenidae* making another stop

The next pollinator is a bee from the same genus, Adrena. This is a huge genus, comprised of more than 450 species in the U.S. Most often they are impossible to identify to species without having the bee in-hand and available for close inspection.

This beautiful and hairy ginger was considerably larger than the previous Andrena. I estimate this bee was about two-thirds the size of the domesticated honeybee.

I’m not sure if this individual was a male, or if it was only interested in getting nectar, but I never saw this species actively collecting pollen from C. virginica.

The long tongue on this one will allow for it to collect nectar from a larger variety of flowers, while the hairs on this bee definitely help it meet its pollinator status.

I found a couple cuckoo bees foraging amoung the C. virginica as well. This “nomad cuckoo” pictured below is a cleptoparasite, meaning the female will lay its egg inside the nest of a different host species. The cleptoparisitc larvae will hatch first and will often kill the eggs or larvae of its host and then use the pollen provisions the host mother left to complete its development. This particular genus, the Nomada, is known to primarily use species in the above discussed Andrena genus as its host.

Cuckoo bee (*Nomada* sp.) nectaring on spring beauty

The cuckoo wasp, like this metalic green beauty in the Chrysididae family are also cleptoparasites that likely will use Adrena bees as hosts.

Cuckoo wasp (Chrysididae) on spring beauty

Bees and wasps were not the only pollinators I found on spring beauty. I also found a couple species of ants (not pictured because they never stand still long enough) and a couple of dipteran species, like this tachinid fly.

Tachinid fly (Gonia sp.) on spring beauty

I now want to introduce what was probably the most interesting thing I learned about spring beauty this year. Having been able to work on Asian Soybean Rust for a couple years during my career, I have since been very interested in the complex life-cycles of plant rusts. I suppose due to the dense population of C. virginica at this location and the cool and wet spring we have had, I found that many plants were infected with spring beauty plant rust (Puccinia mariae-wilsoniae). With just taking a cursory estimation of the hillsides, I think that as many as 50% of this population was infected with this rust. When I took the succeeding photo ( I so wish I had taken more and better photos of this), little did I know that my investigation would take me into a complex relationship that not only involved this plant host and rust relationship, but would also involve slugs (yes slugs) and the very pollinators that enticed me to bend the knee in the first place.

Spring beauty plant rust (*Puccinia mariae-wilsoniae*) aecia (a type of spore forming legion) on the abaxial (lower) leaf surface of spring beauty (*Claytonia virginica*)

I am sure that anyone who has taken the time to appreciate spring beauty more than during one season and/or place has noticed the variability in flower parts coloration. The majority of what is to follow here comes from an intriguing bit of work by Frank Frey (2004). C. virginica can vary from almost completely white to being mostly colored with pink to mauve to crimson stripes and other floral parts. Frank describes that plants that with higher levels of theses reddish pigments are preferred by pollinators and therefore, “…floral redness was associated with higher percentage fruit set.” Well then, this should beg the question, if this is the case why are there still plenty of individuals and populations of the less-fecund whitish pigmented flowers? Shouldn’t selection have taken care of this by now?

Here is where the slugs and rust comes into the story. These two, surprisingly, affect opposing selective forces on the coloration of C. virginica flowers. Plants with more white-colored flowers hold up better against predation by slugs due to the anti-herbivore properties of the flavonol pigments that produce the white coloration in these plants. In addition, for reasons that are not completely understood, the rust pathogen does better at infecting and propagating new spores on plants with redder-colored flowers. This was eye-opening for me to learn that something besides pollinator preference was manifesting a selective force on floral morphologies.

This is a highly simplified summary of the story this paper holds. I highly encourage you to check it out for yourself by following the link below.

An aberrant spring beauty flower. Typical spring beauty flowers have five petals. This plant may be infected by virus or have a genetic mutation that caused the increase in petal numbers seen here.

I love the never ending stories that can be learned from a single, common and seemingly simple spring ephemeral wildflower. I’m sure that spring beauty still has a number of stories to tell. I wish I had taken more photos of the rust and I will try and see if I can find plants with telia, the next form of spore-producing legion by this rust. It occurs later in the lifecycle of the plant. I just hope I’m not too late to get it this season.

Thanks for the visit!

-OZB

Citations

Frey, Frank M. 2004. Opposing natural selection from herbivores and pathogens may maintain floral-color variation in Claytonia virginica (Portulacaceae). Evolution, 58: 2426-2437.

Spring Ephemeral of the Day – Dicentra cucullaria (Dutchman’s Breeches)

macro