Pollinator Handouts

You can now download some of the recent handouts I created for pollinators and native plants from the right sidebar of my blog homepage.

More to come, stay tuned!

American Pasqueflower ~ A Welcome Sign of Spring

American pasqueflower ~ Anemone patens

American pasqueflower is a wonderful native alternative to tulips or daffodils, flowering in early spring. It can be found on sunny, prairie slopes with poor, dry soils. This year, it's flowering before any of the woodland ephemerals such as bloodroot, Sanguinaria canadensis. The leaves are held tight to the stem during flowering, looking like a prop holding the flower upwards. These palmately-divided leaves relax away from the stem and open after flowering.

American pasqueflower provides an abundant amount of pollen to pollinators, an important, early-spring resource for female bees to provision their nests. The plant is protogynous, developing the female parts first (stigmas), with the male anthers shedding pollen after the stigmas are no longer receptive. This is one of many fascinating strategies to ensure cross-pollination. In order to attract pollinators during the male phase, small staminal nectaries located at the base of the stamens produce nectar. It is likely that a visiting insect seeking nectar only will come into contact with the anthers transferring pollen on their bodies to the next pasqueflower.

The flowers when open, track the sun throughout the day turning the flowerheads. This solar tracking (heliotropism) tends to occur in plant families that flower when pollinators are scarce. The flowers facing the sun trap the sun's heat creating a warm place for pollinators to forage and warm body temperatures. The pollinators have little difficulty flying to the next flower when warm, aiding in the cross-pollination of the plant.

Small Sweat Bees, Lasioglossum spp. 
Frequent visitors, small sweat bees collect the white pollen which is abundant, circling around the outside of the numerous stamens on each flower.

Large Mining Bees, Andrena spp.
Large mining bees are common in early spring and can be mistaken for bumble bees. They have shiny, black abdomens, unlike bumble bees who have hairy abdomens. Mining bees nest in the ground in sand or loose, loam soils.

Other pollinators to look for include large syrphid flies feeding on pollen. These flies are mimics of large mining bees and bumble bees. Bumble bees also visit the flowers.

Because American pasqueflower blooms in early spring during fluctuating temperatures, insect activity can be sporadic. If the sepals are closed on a cool day, look for bees forcing their way into the flower.


References:
Bock, J. H., & Peterson, S. J. (1975). Reproductive biology of Pulsatilla patens (Ranunculaceae). American Midland Naturalist, 476-478. Retrieved from: http://www.jstor.org/stable/2424441

Emerald Ash Borer Treatment- Toxic To Bees?

Image Source: Wikipedia

The emerald ash borer, Agrilus planipennis a beetle native to China, Japan and Korea was introduced into North America in the Great Lakes area in the early 1990's and populations were identified in 2002. It is suspected that this beetle was introduced from ash shipping crates. Emerald ash borer beetle larva burrow through the outer bark of ash trees, Fraxinus spp. and into the living cambium tissue.

As the larvae feed on the cambium, they create 'S'-shaped galleries in the wood. The galleries created from a large infestation weaken the ash trees causing canopy thinning and eventually canopy die-back. A secondary symptom is numerous shoots forming around the base of the ash tree.

Current Map of Emerald Ash Borer Range
Source: emeraldashborer.info

As a homeowner living in Minnesota just outside the range of emerald ash borer, I started to research the treatments being offered by local tree care companies. I only have one ash tree on my property and do not plan to treat it but many of the suburban neighborhoods in the Twin Cities were heavily planted with ash trees in the late 1970's and early 1980's. I am reminded when driving through these neighborhoods that planting a diversity of native plant species in your landscape will help with weathering the impacts from invasive species and climate change.

"Systemic insecticides containing the active ingredients imidacloprid, dinotefuran or emamectin benzoate are commonly used to protect ash trees from EAB." (Potential Side Effects of EAB Insecticides) Imidacloprid belongs to the group of neonicotinoid insecticides which has been linked to Colony Collapse Disorder (CCD). Read a recent Xerces Society report here: Are Neonicotinoids Killing Bees? Today, a coalition of bee-keepers have filed a suit against the EPA for failing to suspend the use of neonicotinoid pesticides.

Imidacloprid, sold under the trade names Merit, Xytect, Optrol, ArmorTech, Enforce, Hawk-I, Turfthor, Malice, Premis, Criterion, Hunter, Submerge and Touchstone is typically applied as a soil drench or soil injection annually as a preventative treatment for emerald ash borer. For a homeowner with several ash trees, the cost can be very high. The city of Minneapolis now recommends replacing ash trees on residential properties rather than treating them due to the environmental risks from the treatments including, leaching into the surface or ground water, uptake by other plants visited by pollinators for nectar and pollen and non-target effects on woodpeckers feeding on EAB larvae.

Are your ash trees worth saving or should you be preparing for their replacement? Are the risks of using neonicotinoids too high? Purdue University offers a cost calculator for EAB treatment for homeowners here. Trees with structural defects, poorly sited, or with no historical or aesthetic value should not be treated. Read more guidelines here.

Perhaps our efforts should be focused on the conservation of ash tree species. Volunteers are needed for the collection of ash seeds to help preserve genetic variation and with a long-term goal of the reintroduction of ash trees into affected areas. Find out more information on how you can help collect ash tree seeds.

References:
The Effects of Neonicotinoids on Honey and Bumble Bees.Vera Krischik, Entomology, University of Minnesota.
Chemicals Implicated. BeyondPesticides.org
Blacquiere, T., Smagghe, G., Van Gestel, C. A., & Mommaerts, V. (2012). Neonicotinoids in bees: a review on concentrations, side-effects and risk assessment. Ecotoxicology, 1-20.
Emerald Ash Borer Info

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 Halictus 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

Ten Great Native Plants for Dry, Sandy Soils

Flower: June - Late July  |  Exposure: Full Sun

Soil Moisture: Mesic to Dry  |  Soil Type: Sand to Loam

Butterfly milkweed develops a substantial taproot and is not easy to transplant. Find the right sunny location and let it grow. It is an excellent plant for pollinators, and a larval host plant for the monarch butterfly, queen butterfly and milkweed tussock moth caterpillar.

Flower: Late April - June  |  Exposure: Full Sun

Soil Moisture: Mesic to Dry  |  Soil Type: Sand to Loam

Prairie smoke's most unique feature is the wispy, feathery ends attached to the seeds that persist into the summer and wave in the wind. The fern-like foliage stays green under the snow and is a welcome sight in spring. Prairie smoke is pollinated by bumble bees who use buzz pollination to release the pollen from pores.

Flower: June - September  |  Exposure: Full - Part Sun

Soil Moisture: Mesic to Dry  |  Soil Type: Sand to Loam

Harebell has a fine, dainty form but is very tolerant of tough sites. It's native range covers most of North America except for the southern-most states. It likes high alpine rocky terrain, growing from cracks in rocks on the edge of lake superior and sandy bluffs.

Flower: July - October  |  Exposure: Full - Part Sun

Soil Moisture: Mesic to Dry  |  Soil Type: Sand to Clay/Loam

Stiff goldenrod is a well behaved goldenrod with an upright form and large flat-topped flowerheads. The flowers are very long-lasting and combine well with prairie grasses such as little bluestem. An absolute pollinator magnet in late summer, the shallow disc flowers allow most types of pollinators access to nectar.

Flower: July - September  |  Exposure: Full Sun

Soil Moisture: Dry Mesic to Dry  |  Soil Type: Sand to Sandy Loam

Spotted bee balm can be short lived but if planted in suitable sites will reseed enough to maintain a stand. The interesting whorled/tiered flowers are unique, the lower bracts can range from pink to white in color. If you're looking for a plant that stands out at dusk, this is a good candidate.

It a larval host plant for the gray marvel moth and two snout moths, Pyrausta spp.

Flower: July - September  |  Exposure: Full Sun

Soil Moisture: Mesic to Dry  |  Soil Type: Sand to Loam

Hoary vervain is common in disturbed sites with sandy soils. It is a great performer in the garden, with an upright form and showy flowers arranged on narrow spikes. The flowers open from the bottom upwards and are visited by bees and butterflies for the nectar. It a larval host plant for the verbena moth and fine-lined sallow moth.

Flower: May - June  |  Exposure: Full - Part Sun

Soil Moisture: Dry Mesic to Dry  |  Soil Type: Sand to Sandy Loam

Wild lupine loves sandy soils. It is an excellent perennial for early spring color. The flowers lack nectar but it still attracts bumble bees and mason bees for pollen. It a larval host plant for the endangered karner blue butterfly, as well as several duskywings and sulphur butterflies.

Flower: June - September  |  Exposure: Full - Part Sun

Soil Moisture: Mesic to Dry  |  Soil Type: Sand to Clay/Loam

You can't find a more versatile plant than black-eyed susans. It flowers in its first year from seedlings, reblooms throughout the summer months, and is very showy. It can be short-lived but but reseeds. It a larval host plant for the wavy-lined and southern emerald moths, and the 

silvery checkerspot butterfly.

Flower: June - September  |  Exposure: Full - Part Sun

Soil Moisture: Mesic to Dry  |  Soil Type: Sand to Clay/Loam

Fragrant hyssop belongs to the mint family, and like many plants in this family the leaves are fragrant. If you like black licorice, then you will enjoy nibbling on the leaves of fragrant hyssop. 

It can get quite tall in soils that are too rich - close to 60", but in dry prairies 30" is more typical. It works well to mass this plant which highlights the range in flower colors from light blue to dark 

purple.

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.