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Pollinators in the Landscape I: Importance of Pollinators and Causes of Decline

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Butterflies are important pollinators
Butterflies are important pollinators
Butterflies are important pollinators
Butterflies are important pollinators

Photos by Mandy Bayer

The Importance of Pollinators

Concerns about honeybee populations and monarch butterfly migration have brought attention to the need to protect and support pollinators in the landscape. To understand the importance of pollinators, it is necessary to have an understanding of pollination. There are two types of pollination, self-pollination in which a plant is able to pollinate itself without outside help, and cross-pollination which is pollination aided by animals, wind, and water. The majority of pollination is cross-pollination with animal assisted pollination accounting for around 75%. Pollination is necessary for fruit development, seed production, and can result in better quality of some fruits (such as tomato). Almost all fruit and grain crops grown in the US require pollination (over 150 crops!) and crops dependent on pollinators are estimated by the USDA to be worth more than $10 billion per year.

Pollinator Decline

Pollinator decline is an area of controversy and concern, with the growing consensus being that it is not a singular cause, but a combination of multiple stressors leading to population declines. Pesticides, with a focus on neonicotinoids, are one of the most controversial contributors to decline. The concern with pesticides and herbicides is twofold: 1) the direct health implications of pesticides on pollinators and 2) the use of herbicides in cropping systems, which creates monocultures that poorly support pollinators by reducing the variety of flowering plants in the area. The issue with neonicotinoid insecticides is that they travel systemically throughout the plant, including to pollen and nectar, increasing the likelihood of pollinator contact.

Loss of suitable habitats is another cause of concern. Urbanization and land conversion have contributed to loss of habitat. A combination of habitats is needed for food, nesting and mating areas, and migration. Urbanization has led to the fragmentation of habitats and the disruption of some migratory pathways. Land conversion from diverse natural landscapes to intensive cropping areas that are almost monocultures, decreases the variety of pollen and nectar sources for pollinators. Flowers vary in protein content and nutrient composition, so a diet of a singular plant species has the potential to impact pollinator health.

Transportation of bees and an increase of commercial bee colony trade have contributed to the spread of parasites and diseases outside of the normal range. The spread of parasites and pathogens is problematic because the new host species often lacks resistance, increasing the likelihood of death.

The impact of current and future climate change on pollinators is not yet well understood. Historically, changes in climate have caused the native ranges of plants and animals to shift to where conditions are more favorable. Many plants and pollinators have evolved to have a mutualistic dependency, so with potential range shifts there is concern that plant and pollinators will shift in different directions. Range shifts due to climate change have already been observed with some butterflies. Another concern is the alteration of bloom time and pollinator emergence. Climate change has the potential to lead to earlier warmer temperatures in the spring, which could disrupt the synchronization of flower development and pollinator emergence. There may also be increased potential for flower and bud damage due to increased frequency of late frost events if warmer temperatures come early.

The good news is that urban landscapes have great potential to support pollinators, both as nectar and pollen sources and as pollinator habitats.

Pollinator Plant Spotlight: Milkweed

Milkweed (Asclepias spp.) is the larval host plant for the monarch butterfly, meaning that milkweed is the only plant that monarch caterpillars feed on. Many plants and their pollinators have evolved together creating mutualistic dependencies. Milkweed contains toxins that are not harmful to monarch caterpillars, but are poisonous to many animals, providing protection for monarchs both as larval caterpillars and as adult butterflies.

Milkweed species for the Northeast:

Asclepias incarnata

Swamp milkweed

Asclepias tuberosa

Butterflyweed

Asclepias verticillata

Whorled milkweed

Asclepias exaltata

Poke milkweed

Pollinator Highlight: Butterflies and moths

Butterflies have four life stages: egg, caterpillar, pupa, and adult; all of which have differing habitat needs. There are many habitat options for butterfly eggs including leaves or branches of various plants and the soil. Larval, or caterpillar, host plants are much more limited (for example Monarch butterflies and milkweed) and need to provide the caterpillar with both food and shelter. At the pupa stage butterflies need a protected area, such as shrubs, tall grasses, or fallen branches. As adults, butterflies need plants that provide a nectar source. Butterflies are attracted to flowers that are brightly colored, open during the day and provide a good landing platform. Nectar is usually deeply hidden within the flower; however butterflies are able to use nectar guides to find nectar. Nectar guides are markings on flowers that are not visible to humans but can be seen by pollinators and direct them to nectar. While some butterfly species migrate in the winter, others hibernate, requiring leaf litter, bark, or other landscape debris as cover.

Moths can be either nocturnal or day-time pollinators depending on the type, with the majority being nocturnal and very important for the pollination of night blooming flowers. They are generally attracted to white or dull colored flowers that are heavily fragranced.

Plant features for attracting butterflies include:

  • Bright colored flowers
  • Wide landing pad
  • Tubular flowers

Plant features for attracting moths include:

  • Pale/dull colored flowers
  • Strongly sweet fragrance (especially at night)
  • Tubular flowers

Plants for Butterfly Gardens

Plants that attract butterflies (nectar sources):

Annuals

Scientific Name

Common Name

Size

Color

Bloom Time

Cosmos bipinnatus

Cosmos

12-48"

pink, red, white

June to frost

Lantana camara

Lantana

36-48"

yellow, pink, white, orange, red, purple, mixed

July to frost

Tagetes erecta

African marigold

12-48"

yellow, orange, white

June to frost

Tagetes patula

French marigold

6-12"

yellow, orange, red, bicolor

June to frost

Tithonia rotundifolia

Mexican sunflower

48-72"

orange-red

July to September

Tropaeolum

nasturtium

12-36"

red, orange, yellow, or cream

May to September

Zinnia spp.

zinnia

6-48"

red, orange, yellow, pink, white, purple, cream

June to frost

Perennials

Scientific Name

Common Name

Size

Color

Bloom Time

Native

Allium cultivars

ornamental onion

12-60"

purple, lavender

May-June

 

Asclepias incarnata

swamp milkweed

48-60"

white, pink, mauve

July - August

*

Asclepias purpurascens

purple milkweed

24-36"

pink to purple

May- July

*

Asclepias tuberosa

butterfly weed

12-30"

yellow/orange

June-August

*

Aster spp.

Aster

12-24"

purple, blue, lavender, white

August - September

some

Coreopsis cultivars

tickseed

12-24"

yellows

June - October

 

Coreopsis rosea

tickseed

12-36'

pink

June - September

*

Dianthus barbatus

sweet William

12-24"

red, pink, white, bicolor

May - frost

 

Echinacea cultivars

coneflower

6-48"

purple, pink, white, yellow, orange, lime

June - August

 

Echinacea purpurea

purple coneflower

24-60"

purple/pink

June - August

*

Eutrochium purpureum

Joe Pye weed

60-84"

pink

July - September

*

Gaillardia spp.

blanketflower

8-36"

yellow, orange, red

May - September

 

Helenium cultivars

sneezeweed

12-48"

red, orange, yellow

August - October

 

Lavandula angustifolia cultivars

English lavender

8-36"

purple, lavender, pink, blue

June - October

 

Leucanthemum x superbum

shasta daisy

22-36"

white

July - September

 

Liatris spicata

blazing star

8-18"

purple

July - August

*

Lobelia cardinalis

cardinal flower

24-48"

red, white, or pink

July - September

*

Lobelia siphilitica

blue cardinal flower

24-36"

blue

July - September

*

Monarda cultivars

bee balm

8-36"

reds, pinks, or purples

June - August

 

Phlox paniculata cultivars

garden phlox

12-48"

pink, red, white, purple, lavender, bicolor

July - September

 

Phlox subulata

creeping phlox

4-6"

red, purple, lavender, pink, white

March - May

*

Rudbeckia fulgida

black-eyed Susan

24-36"

yellow/orange

June - October

 

Scabiosa 'Butterfly Blue'

pincushion flower

12-18"

lavender blue

April - frost

 

Sedum spp.

stonecrop

2-18"

pink, red, white

July - September

 

Symphyotrichum novae-angliae

New England aster

36-72"

deep pink purple

August - September

*

Shrubs and Trees

Shrubs

Scientific Name

Common Name

Size

Color

Bloom Time

Native

Aesculus parviflora

bottlebrush buckeye

8-12'

white

June-July

 

Buddleja alternifolia

alternate-leaved butterfly bush

8-15'

lilac purple

May

 

Buddleja davidii cultivars

butterfly bush

3-12'

lilac, purple, pink, red, white

June - September

 

Ceanothus americanus

New Jersey tea

3-4'

white

May - July

*

Cephalanthus occidentalis

buttonbush

5-12'

white

June

*

Clethra alnifolia and cultivars

sweet pepperbush/ summersweet

2-8'

white, pink

July - August

*

Fothergilla gardenii

dwarf fothergilla

1.5-3'

white

April-May

 

Kalmia latifolia cultivars

mountain laurel

2-15'

pink, white, multicolor

May - June

*

Kolkwitzia amabilis

beautybush

6-10'

pink

April-May

 

Lindera benzoin

spicebush

6-12'

yellow/green

March

*

Rhododendron spp.

Rhododendron and azalea

       

Syringa vulgaris cultivars

common lilac

3-16'

lavender, purple, white, pink, blue

May

 

Vaccinium spp./cultivars

blueberry

3-12'

white

May

*

Viburnum spp.

viburnum

2-20'

white

April - June

some

Trees

         

Aesculus glabra

Ohio buckeye

20-40'

greenish yellow

April - May

 

Amelanchier spp.

Serviceberry

6-25’ white April - May *

Cornus florida and cultivars

flowering dogwood

15-30'

white, pink

April - May

*

Malus cultivars

flowering crabapple

7-30'

white, pink, coral

   

Prunus spp.

cherry, flowering almond

10-40'

white, pink

March - April

 

Host Plants (plants that caterpillars like to feed on):

Larval Host Plants

Scientific Name

Common Name

Size

Native

Alcea rosea

hollyhock

5-8'

 

Anethum graveolens

dill

3-5'

 

Asclepias spp.

milkweed

24-60"

 

Artemisia spp.

wormwood

6-36”

 

Aster spp.

aster

12-24”

 

Carex

sedge

0.5-1.5'

 

Echinacea purpurea

coneflower

18-36”

 

Panicum

switch grass

2.5-6'

 

Petroselinum crispum

parsley

0.5-1'

 

Schizachyrium scoparium

little bluestem

2-4'

 

Sedum spp.

stonecrop

2-18"

 

Viola spp.

violet

4-12"

some

Aesculus glabra

Ohio buckeye

20-40'

 

Amelanchier spp.

serviceberry

15-30'

some

Betula spp.

birch

30-70'

some

Carpinus caroliniana

hornbeam

20-35'

*

Ceanothus americanus

New Jersey tea

3-4'

*

Cephalanthus occidentalis

buttonbush

5-12'

*

Cercis canadensis

redbud

20-30'

*

Clethra alnifolia and cultivars

sweet pepperbush/ summerweet

2-8'

*

Cornus florida

flowering dogwood

15-30'

 

Cornus alternifolia

pagoda dogwood

15-25'

 

Fraxinus spp.

ash

35-80'

some

Lindera benzoin

spicebush

6-12'

*

Populus spp.

poplar, aspen

30-80'

some

Quercus spp.

oak

30-80'

some

Rhododendron spp.

rhododendron and azalea

2-12'

some

Rhus spp.

sumac

1.5-30'

some

Sassafras albidum

sassafras

30-60'

*

Salix spp.

willow

20-40'+

some

Syringa vulgaris cultivars

common lilac

3-16'

 

Vaccinium spp./cultivars

blueberry

3-12'

*

Viburnum spp.

viburnum

2-20'

some

Ulmus spp.

elm

30-80'

some

Sources:

Goulson, D., E. Nicholls, C. Botias, and E.L. Rotheray. 2015. Bee declines drive by combined stress from parasites, pesticides, and lack of flowers. Science 26 Feb 2015.

USDA Forest Service. Pollinators. https://www.fs.fed.us/wildflowers/pollinators/animals/

USDA Forest Service. Plant Milkweed for Monarchs. https://www.fs.fed.us/wildflowers/pollinators/Monarch_Butterfly/documents/MilkweedInfoSheet.pdf

University of Maine Extension. Landscaping for Butterflies in Maine. https://extension.umaine.edu/publications/7151e/

Massachusetts Butterfly Club. http://www.naba.org/chapters/nabambc/downloads/Butterfly%20gardening%20101%20-%20Western%20Massachusetts.pdf

USDA Natural Resources Concervation Service and the Wildlife Habitat Council. Native Pollinators. https://plants.usda.gov/pollinators/Native_Pollinators.pdf

UMass Center for Agriculture Food and the Environment. Protecting Bees and Pollinators from Pesticides in Home Gardens and Landscapes. https://ag.umass.edu/home-lawn-garden/fact-sheets/protecting-bees-pollinators-from-pesticides-in-home-gardens-landscapes

Missouri Botanical Garden Plant Finder http://www.missouribotanicalgarden.org/plantfinder/plantfindersearch.aspx

Author: 
Mandy Bayer
Last Updated: 
May 6, 2015
Topics: 
Commercial Horticulture
Commercial Horticulture topics: 
Insects and Mites