Pollination of Downy Yellow Violets ~ An Upside Down Approach

Downy Yellow Violets ~ Viola pubescens
Downy yellow violets are one of my favorite woodland violets. The heart-shaped leaves set off the bright yellow flowers in early spring. Because of its short stature (6-12"), I use this violet on woodland borders, intermixed with Pennsylvania sedge, rue anemone and virginia waterleaf.

The flowers are attractive to pollinators, especially small bees. The lower petal acts as a nice landing platform and the bold black stripes guide the visitors to the nectar. Nectar is secreted from a gland-like spur on the bottom anthers which are shortened and form a ring around the ovary.

Bees with short tongues such as this shiny, blue, small carpenter bee, Ceratina sp. have a hard time reaching the nectar in the spur. In order to reach the reward, they turn their bodies upside down.

Long-tongued bees like bumble bees stay right side up and push their head into the flower.

Both the right side up and upside down positions cause the style to be pushed upwards. When a right side up bee inserts its head into the flower, the cone formed by the stamens is opened, releasing pollen onto the top of the visitor’s head and thorax. In the upside down position, insects land on the front petal and turn themselves upside down. The style is pushed upwards and pollen is released on the face and lower abdomen of the visitor. Subsequent visits to other violets transfer pollen to the receptive stigma.

Small sweat bees, Lasioglossum sp. are also upside down visitors.

They push their head into the flower as far as possible to try and reach the nectar reward.

Other visitors of downy yellow violet include bee flies (Bombylius sp.), clouded sulphur butterflies (Colias philodice) and Syrphid flies.




References:

Beattie, A. J. (1974). Floral evolution in Viola. Annals of the Missouri Botanical Garden, 781-793. Retrieved from: http://www.jstor.org/stable/2395029

Wild Geranium Pollinators & Floral Visitors

Like many spring-flowering native plants, wild geranium flowers have the ability to self-pollinate when no pollinators are present. However, the flower matures to ensure cross-pollination when insects are present, with the row of outer anthers developing on the first or second day after the flowers open, followed by the inner row on the second or third day. The stigma becomes receptive after the anthers have dehisced on the third or forth day.

Bees, flies and beetles visit the flower for nectar and pollen. Nectar is secreted from five glands located between the stamens and sepals. In a study by Bertin et al, bees visiting for nectar were responsible for depositing more pollen than pollen collecting bees. Larger bees such as bumble bees and mason bees are considered effective pollinators because pollen brushed onto the underside of their abdomen contacts the stigma. Smaller bees are able to circle around the base of the stamens feeding on nectar without coming into contact with pollen from the anthers above.

Wild geranium flowers are over one inch in width and extremely showy. Dark lines on the flowers act as nectar guides, showing pollinators the location of the nectaries at the base of the stamens.

Small Carpenter Bees, Ceratina spp.
Smaller bee species circle the base of the flower seeking out nectar without coming in contact with the anthers and stigmas above.

Cuckoo Bees, Nomada spp. 
Wild geranium is a nectar source for this cuckoo bee in early spring. Female Nomada bees lay their eggs in the nests of ground nesting native bees, especially mining bees (Andrena spp.). The cuckoo bee eggs hatch and the larvae kills the host bee larvae and consumes the provisions provided by the host. Nomada bees are reddish-brown to black with yellow or white markings.

Mason Bees Osmia spp. 
Mason bees visit wild geranium for both pollen and nectar. Females land on top of the anthers gathering them together with her legs. Pollen is brushed onto the pollen-collecting hairs on the underside of the abdomen. Wild geranium is an important source of pollen and nectar for mason bees, it flowers when females are provisioning their nests.

Sweat Bees Lasioglossum spp.
Sweat bees visit the flowers to feed on nectar.

Fruitworm Beetles Byturus unicolor 
Long, dense hairs cover the elytra of these beetles where pollen grains attach. Adults emerge from the soil in early spring, feed on host plants (raspberries, blackberries and avens), mate, then lay eggs. Larvae burrow into the flower buds and fruit of the host species and buds drop off or decay. Fruit becomes misshapen and ‘wormy’. Look for adult beetles feeding on the pollen of woodland natives in early spring such as Viriginia waterleaf and wild geranium.


References 
Bertin, R. I., & Sholes, O. D. (1993). Weather, pollination and the phenology of Geranium maculatum. American Midland Naturalist, 52-66. Retrieved from: http://www.jstor.org/stable/2426435

Willson, M. F., Miller, L. J., & Rathcke, B. J. (1979). Floral display in Phlox and Geranium: adaptive aspects. Evolution, 52-63. Retrieved from: http://www.jstor.org/stable/2407365

Milkweed Pollination - A Sticky Situation

Milkweed plants, Asclepias spp. have a unique method of transferring pollen from one plant to the other for cross-pollination. Pollen is aggregated in sac-like bundles called pollinia, located on either side of the stigmatic chamber. The two bundles are strung together with a gland (filament) at the top of the stigmatic chamber.

Bees, wasps, flies, beetles and butterflies visit the flowers for nectar. Milkweed plants typically produce a lot of nectar, it is replenished overnight, to the delight of nocturnal moths, and the remaining nectar is ready for the first diurnal visitors in the morning.

For accessing nectar, floral visitors prop themselves on one of the five flower hoods, sliding their tongues down the side of the hood where the nectar is held. They must be careful not to slip their leg down into the flower between the anthers.

When pulling their leg out, they could snag it on the filament holding together the sticky pollinia sacs.

Pollina stuck to the legs of a great
black wasp, Sphex pensylvanicus

The sticky pollinium sacs are carried to other milkweed plants on their legs and if the insect again ‘slips’ the pollinia can be inserted into the stigmatic chamber ensuring cross-pollination. Unable to pull their leg out, smaller bees can become trapped in the flowers and perish.

In a study by Fishbein and Venable (1996), small- and medium-sized bees, and medium-sized butterflies had the lowest removal rates of pollinia. Their study found that it was the larger bees, like bumble bees that were most effective at transferring pollinia from one plant to the other.

Leafcutter bee, Megachile sp. alighting
on top of the flower hoods to nectar.

Ivey et al. (2003), also found large carpenter bees, Xylocopa spp. and bumble bees, Bombus spp. effective pollinators, partly due to their foraging efficiency; they visit flowers methodically, probing all the hoods of a flower, and visiting more flowers per flowerhead.


Leafcutter bees are common visitors of milkweed feeding on nectar. They rarely snag pollinium sacs so are considered ineffective pollinators.

Small carpenter bees, Ceratina spp. prop themselves on the top of the hood and slide their tongue down the side of the hood to reach nectar.

Cuckoo bees, Coelioxys spp. are true nectar thieves. The have no pollen-collecting structures on their legs. They only visit flowers for nectar because they are cleptoparasites, laying their eggs in the nests of other bees.

This particular cuckoo bee is a cleptoparasite of leafcutter bees,  Megachile spp. Females have a tapered abdomen ending in a sharp point that is used to break through leafcutter brood cells.

Another example of a small-sized bee, yellow faced bees, Hylaeus spp. are frequent visitors to swamp milkweed in late summer for nectar.

Soldier beetles, Chauliognathus spp. also love to feed on nectar on milkweed plants but are rarely found carrying pollinia.

What seems to be a not-so-mutualistic relationship between floral visitor and plant, where floral visitors are exploiting nectar resources, cross-pollination is still occurring due to the effective visitation by large bees, who transfer the polllinium sacs from one plant to another.


References
Fishbein, M., & Venable, D. L. (1996). Diversity and temporal change in the effective pollinators of Asclepias tuberosa. Ecology, 1061-1073.

Ivey, C. T., Martinez, P., & Wyatt, R. (2003). Variation in pollinator effectiveness in swamp milkweed, Asclepias incarnata (Apocynaceae). American Journal of Botany, 90(2), 214-225.

Kephart, S. R. (1983). The partitioning of pollinators among three species of Asclepias. Ecology, 120-133.

Plan Now for Spring Pollinators

Tall Beard Tongue Insect Visitors

Tall Beard Tongue ~ Penstemon digitalis
Beard tongue flowers have a large, hairy staminode on the lower half of the tubular flower which restricts access to bees to the flower and helps in pollen deposition. Small to medium sized bees are the most frequent visitors.

Tall Beard Tongue flowers can be white to light pink, sometimes with darker pink to purple stripes which act as nectar guides for bees.

Small Carpenter Bees (Ceratina spp.) visit Tall Beard Tongue flowers primarily to feed on pollen. Their small size allows them to easily climb over the staminode into the tubular flowers to access the pollen on the anthers.

As they feed on pollen, they often inadvertently contact the stigma. The hairs on the staminode keep their bodies held closer to the stigma, resulting in more contact and pollen transfer.

Digger Bees (Anthophora spp.) are frequent visitors to Tall Beard Tongue flowers as well. They are fast moving and visit flowers for a very short time frame compared to Small Carpenter Bees.

Their medium sized bodies and long tongues allow them access into the tubular flower which results in abundant pollen removal as their bodies scrape on the anthers above.

Bumble Bees (Bombus spp.) are not primary pollinators of Tall Beard Tongue. Visiting the flowers for nectar, they are able to reach the nectar reward with their long tongues without having to insert their body into the corolla and come away with pollen on their bodies.

Look for small holes chewed at the base of the flower. Mason Wasps will chew holes to reach the nectar reward without having to enter the flower. Smaller bees will take advantage of these nectar thievery holes.




References:
Attracting Native Pollinators: The Xerces Society Guide, Protecting North America's Bees and Butterflies

The Interaction between Pollinator Size and the Bristle Staminode of Penstemon digitalis (Scrophulariaceae) Gregg Dieringer and Leticia Cabrera R. American Journal of Botany , Vol. 89, No. 6 (Jun., 2002), pp. 991-997

Wild Lupine Insect Visitors

Wild Lupine ~ Lupinus perennis 

Wild Lupine is a native perennial of dry, sandy sites in full sun. Flowering from late April/early May into June, the flower color ranges from light blue to dark purple.

Because of its early flowering time, overwintering queen Bumble Bees or their female offspring will visit the flowers. The irregular flower form means that the larger Bumble Bees don't have too much difficulty prying open the lower wing petals to reveal the reward inside.

Bombus auricomis

According to Illinois Wildflowers, there is no nectar reward provided by Wild Lupine, and pollen is forcibly ejected into the faces of bees.

Butterflies and moths will visit the flowers looking for nectar but come away with no reward. I photographed this Hummingbird Clearwing Moth this spring on our Wild Lupine flowers.

I also observed many Mason Bees (Osmia spp.) visiting Wild Lupine flowers this spring. They start with their rear legs prying open the petals, get a start on it opening, then use their mid and forelegs to hold the flowers open.

Wild Lupine and Mason Bees were built for each other, as Mason Bees collect pollen on their abdomens. Perfect for where the fused stamens are located just above the bottom keel, rubbing off some pollen for cross-pollination onto the Mason Bee abdomen.

Look for Mining Bees (Andrena spp.) a ground nesting native bee that emerges in early spring and visits flowers to collect pollen and nectar for nest provisioning.

Small Carpenter Bees (Ceratina spp.) also look in vain for nectar on flowers that have been forced open and are accessible as they cannot pry open the petals themselves.

Wild Lupine is a larval host plant to several butterfly and moth species, the most notable is the specialist Karner Blue Butterfly (Lycaeides melissa) an endangered butterfly.

Native Bee Spotlight: Small Carpenter Bees ~ Ceratina spp.

Small Carpenter Bee
on Hepatica flower

Small Carpenter Bees ~ Ceratina spp.

In my landscape, I start to see Small Carpenter Bees in March when the first woodland ephemerals are blooming.

Small Carpenter Bees are very tiny, for identification I look for white markings on the face and a shiny blue-green to black body. Not all species have white on the face although.

Small Carpenter Bee on
Wild Geranium ~ Geranium maculatum

These native bees nest in cavities of plant stems. Females will chew holes through the center of soft, pithy wood and create a nesting cavity. The female "places herself as a guard at the entrance. She will die during the winter but remains in place to block the nest access." (Attracting Native Pollinators, p. 248.)

Small Carpenter Bee
visiting Virginia Waterleaf

Leaving dead plant material in your landscape standing helps provide habitat for cavity nesting bees. If you have Elderberry species, think of those soft wood branches that often die back significantly each season providing nesting habitat.

This Small Carpenter Bee is visiting a Bluestar flower (Amsonia spp.) looking for available nectar and pollen.

Small Carpenter Bees continue to visit my native perennials throughout the spring into July. Pictured here on Ohio Spiderwort (Tradescantia ohiensis).

Also Harebell (Campanula rotundifolia). Their small size gives them an all access pass to small open flowers.

Look for these bees also on Beardtongue (Penstemon spp.),

Butterfly Milkweed (Asclepias tuberosa),

Wild Petunia (Ruellia humilis),

and Prairie Coreopsis (Coreopsis palmata).