Monday, March 3, 2014

Managing Milkweed Aphids

Inviting Syrphid Flies for Lunch!

Syrphrid Fly - Hover Fly
Syrphrid Fly - Hover Fly

  How to best deal with Milkweed Aphids (Oleander aphids) which have a preference for Asclepias species (milkweed) has created a bit of a dilemma for sometime now.

    As an aspiring organic farmer, applying pesticides is out of the question, besides it doesn’t make sense to raise native plants only to exterminate insects one attracts. In addition, there is risk of accidentally damaging butterfly eggs and larvae.

    In the past, I devised a strategy which temporally outwitted those six legged beady-eyed, mustard colored aphids; I sold milkweed plants early in the season, before they flowered. This provided a reasonable solution as typically aphids infest our plants late in the summer. It quickly became apparent that customers preferred purchasing plants in bloom, especially ones they were not familiar with. Another possible course of action was to wipe down each plant. Not only does that mask the problem, I honestly don’t have the time or patience for it.



Dealing With Milkweed Aphids

   The reality is, once Asclepias plants have been purchased and planted, there is a fairly good chance local aphids will discover them! Other articles suggest using a powerful spray to blast them out of the universe. From my experience, yes they are sent flying but only to return a bit soggy and bedraggled the next day.

Butterfly Weed - Asclepias tuberosa
Butterfly Weed - Asclepias tuberosa
    In 2013 at NOG our aphid population was noticeably less than the previous year, even though our milkweed inventory had doubled. I considered the fact that the hot dry summer may have played a role. My hunch was correct. According to author H.J.McAuslane, at the University of Florida, decreasing water and fertilizer levels tends to reduce milkweed aphid populations.

   Douglas Tallamy, in his book "Bringing Nature Home" confirms this, explaining second generation winged aphids forge for nitrogen, found in phloem of asclepias stems. 

Milkweed aphids
Milkweed Aphids
  Phloem, under pressure transports: carbohydrates (sugars), hormones, amines (amino acids: asparagine, glutamine, aspartic acid) and other organic materials from the leaves to the roots. Sounds like a nourishing meal for hitch-hiking aphids!
  Is it then possible to provide a less desirable gourmet feast without sacrificing the health and quality of our plants? Perhaps, if our entrees were a bit less palatable, Oleanders would head towards I 90 with thumbs held high!

“What are Natural Predators of Oleander Aphids?” 

Gray-headed Coneflower
Gray-headed Coneflower
  Managing water and fertilizer levels is easier said than done. I am  bit concerned, that decreasing sugar levels may have an adverse effect on roots surviving harsh Ohio winters?

  I decide to approach this from a different direction, “What are the natural predators of the Oleander Aphids?” Fortunately, this question was answered in a thread on the website What's That Bug?

  As it turns out I was correct in assuming that hosing down aphids doesn’t eradicate the problem, as a matter of fact a powerful spray actually drowns natural predators like the larvae of the Lacewing and Syrphid Fly (Hover Flies). 

  For the sake of time and length of the post, I decide to concentrate on discovering how to attract Hover Flies. Hover flies do indeed hover like helicopters; flying both forward and backwards, maybe inside out and upside down. They resemble bees but have only one set of wings not two, are less harry and actually do have beady little eyes. Larvae are especially ravenous, consuming up to 400 aphids during their growth period. Now these guys you want to invite to lunch!

  “What Native Plants Attract Syrphrid Flies?”

Golden Alexander
Golden Alexander - Apiaceace Family
  The second question then became, “What native plants will attract Hover Flies?” Back in September 2013, I presented my question on the website What's That Bug? This was their response. 

You can attract Syrphid Flies with blossoms, especially those in the composite family Asteraceae and umbel blossoms in the families Apiaceae and Alliaceae. We always let some of our carrots and onions go to blossom because of the beneficial insects they attract."


Pale Sunflower
Pale Sunflower - Asteraceae Family

  Asteraceae (Aster) Family includes a large number of plants like: Joe-Pye-Weed, Downy Sunflowers, Purple Coneflower, New York Ironweed and Purple-headed Sneezeweed. We raise only two native plants in the Apiaceae (carrot) Family: Golden Alexander and Rattle Snakemaster and one in the Alliaceae (Onion) Family, Nodding Onion (Allium cernuum). However, the USDA Department of Natural Resources list Nodding Onion as being in the Liliaceae family. 

    Regardless of how Nodding Onion is categorized it is apparent we have room for improvement when it comes to raising a more diverse group of native plants.

  In Heather Holm's new book, Pollinators of Native Plants, Attract, Observe, and Identify Pollinators and Beneficial Insects with Native Plants. Holms mentions: Swamp Marigold (Ranunculaceae Family), Ohio Spiderwort (Commelinaceae Family,) Purple Prairie Clover ( Fabaceae Family) and numerous other native plants as attracting Syrphid flies to consume pollen, nectar, or both. How exciting! The list of native plants which one can expect to “lure” in Hover Flies includes more plants than I expected!




A Few of our Native Plants That Attract Syrphid Flies



New England Aster
New England Aster - Asteraceae Family

Brown-eyed Susans
Brown-eyed Susans - Asteraceae Family

Rattle Snakemaster
Rattle Snakemaster - Apiaceace Family

Cup Plant
Cup Plant - Asteraceae Family

Purple Coneflower
Purple Coneflower - Asteraceae Family

New York Ironweed
New York Ironweed - Asteraceae Family



Strive for Diversity

  It really isn't important if you plant 5 native plants in family "A" or six in family "B" what really matters is diversity/variety. Experiment! Try growing one or two new native plant species each year. Consider raising them from seed, although a bit more work it is extremely rewarding. Grow your favorite annuals, herbs and vegetables, they too attract native pollinators. 

  Make a point to familiarize yourself with your region's non-native, invasive species. What resource zappers they are, taking more than their share of: water, garden space and soil nutrients. Chance are, Hover Flies won't even give them a second glance!

The Tricky Part is Stepping Back and Letting the "Picnic" Begin! 



Holm, Heather. Pollinators of Native Plants Attrqact, Observe and Identify, Pollinatorsa and Benificial Insects with Native Plants. Portland, Or.: Timber, 2007. Print.
Mader, Eric. Attracting Native Pollinators: Protecting North America's Bees and Butterflies: The Xerces Society Guide. North Adams, MA: Storey Pub., 2011. Print.
Tallamy, Douglas W. Bringing Nature Home: How Native Plants Sustain Wildlife in Our Gardens. Portland, Or.: Timber, 2007. Print.Bartlett, 

 Bartlett, Troy."Family Syrphidae - Syrphid Flies". Bug Guide. Iowa State University Entomology. 16 February, 2004
 Berry, R. E. and L. B. Coop . "Syrphid Predator Identification.." Integrated Pest Management on Peppermint - IPMP3.0 [online]. Publication No. IPPC E.01-01-1. Oregon State University, Department of Entomology and Integrated Plant Protection Center, Corvallis, OR.  [published 24 October 2000].
University of California Division of Agriculture and Natural Resources, Publication 828, May 2008
Garvey, Keatley, Kathy. "Syrphid Fly". California Master Gardener Progarm. University Of California Cooperative Extension, 16 Dec 2010.
Marlos, Daniel. "Syrphid Fly Larvae eat Oleander Aphids on Milkweed." What's That Bug?. 9 Sept., 2013.

"Oleander Aphid - Aphis Nerii Boyer De Fonscolombe." Oleander Aphid - Aphis Nerii Boyer De Fonscolombe.
"Phloem vs Xylem." - Difference and Comparison.
Reveal, James. "YYPG by Family". Plant, Department of Plant Biology Cornell University. 24 May 2013
Saupe, Stephen. "Solute Transport:  "Phloem Structure & Function." Home Page - Stephen G. Saupe. College of St. Benedict/St. John's University,Collegeville, MN, Jan. 7, 2009. Mar. 2, 2014.
 Weems, HV. "A Hover Fly, Allograpta obliqua (Say) (Insecta: Diptera: Syrphidae)", University of Florida IFSA Extension. 2013


  1. Excellent post! I know where some of my Ironweed will be planted! On my list of perennials to get this year is New England Asters and I already have Brown Eyed Susans, so I feel better already about those little buggers!


  2. Beth, You have such a wide range of flowers and vegetables growing in your yard (in summer) I would be surprised if you have a problem with aphids. It will be fun to watch and see what happens!

  3. Both the milkweed and aphids are keystone species, providing forage and prey for many other insects. I have seen lots of flower flies on umbellifers, including cilantro/coriander, parsley, and Queen Anne's Lace.

  4. Thank you Pam, What a bonus with the parsley and cilantro, they attract natural predators and you can use them in the kitchen!