We had some questions about the bright yellow aphids show up on milkweeds each year.
Oleander aphids
Where did the aphids come from?
Oleander aphids, Aphis nerii, are thought to have been introduced throughout the world from the Mediterranean region, where oleander is native (the species name nereii comes from Nerium, the genus name for oleander). The aphids are now found over much of North America, where they also use milkweeds and a few related plants as hosts.
How do the aphids reach my plants?
Each spring, when the temperatures and other weather conditions are just right, winged females are blown long distances on the wind. When the air becomes calm, the aphids can make directed flights to host plants. Experts have failed to find male oleander aphids in North America, so they believe the winged females produce young without mating (called parthenogenesis). The first offspring are female aphids without wings. The aphids continue to give live birth to more aphids until conditions cause winged forms to be produced. The winged forms move on again.
Why are they yellow?
Like the monarch and related butterflies, these aphids pick up the toxic cardiac glycosides from the milkweed in their bodies. Their bright yellow-orange color serves as a warning to anything that tries to eat them. The chemicals also are secreted from their cornicles (the tiny black tubes on their rear ends).
Does that mean nothing will eat them?
Unlike many other introduced insects, oleander aphids have a number of parasites and predators. You may have seen the results of tiny wasps (for example, Lysiphlebus testaceipes). The female wasp lays its egg by inserting its ovipositor within the young aphids. The wasp’s larva then eats the aphid’s insides. When the parasite goes through metamorphosis into a pupa inside the body of the aphid, it causes the body of the aphid to turn brown, tan or black, and stiffen. This immobile aphid is referred to as a “mummy.” When the wasp emerges from the pupa, it cuts a hole in the back of the aphid’s abdomen and flies away, leaving the aphid’s empty body.
Flower fly larvae and small lady beetles will also eat oleander aphids.
Flower fly (Syrphidae) larva eating an aphid.
Flower fly adults feed on flowers and are pollinators (see below).
What should I do about oleander aphids on milkweed?
Let’s face it, aphids have a negative reputation. Virtually every gardening book you pick up will list aphids under the “pest” section. These labels are made by humans, however, not the plants or insects. The first thing to realize is that there are a lot of different kinds of aphids, and each species has its own special way of doing things. Often the aphids that are pests are introduced species, with no or few natural enemies, living on introduced plants growing under less than optimal conditions. Other species of aphids are much more benign. If you are willing spend some time observing the insects you find on milkweed, I think you may be surprised. Believe it or not, you might even find that you like them better once you get to know them.
I have had oleander aphids on my milkweed plants (Asclepias subulata) for 20 years. Every year I do absolutely nothing to them. Every year the wasps appear, the mummies build up and the aphids disappear. The main plant is 20 years old, huge and healthy. The other milkweed plants are also growing well. I don’t see any evidence that the aphids are doing harm. Why not leave yours alone for a week or two and see what happens?
What about monarch and queen caterpillars? Will aphids hurt them?
Frankly, you are much more likely to do harm by knocking off eggs and small larvae while trying to control the aphids.
You also might consider that although we humans think that monarch caterpillars eat only milkweed, no one told the monarchs that. Several species of caterpillar are carnivorous (eat insects), including a species that feeds on sundew plants and eats the insects the sundew traps. I would not be at all surprised to find out that monarchs eat an aphid or two from time to time.
Bottom Line:
You can read all sorts of things on the Internet these days. My advice is to be interested and patiently observe what is going on in your own landscape. Do the aphids go away? Do the plants look okay? Do you have a lot of monarch larvae survive? Each situation is unique, and with time and willingness to investigate with an open mind, nature can answer your questions.
Flower fly (Syrphidae) adult
P.S. Of course I am interested in ants and aphids. I have never seen ants tending oleander aphids here. Have you ever seen ants tending this species?
Welcome to the Diversity in Science Carnival #8 in honor of Women’s History Month. Thanks to all of you who submitted posts.
Women have long been prevented from having scientific careers. Responsibilities for raising a family, duties within a community, local customs, rules, and laws have been barriers preventing women from becoming scientists, engineers or mathematicians. But even those tenacious women who overcame the many hurdles and succeeded in their profession are now in danger of disappearing from history, as their stories are forgotten. In honor of this year’s theme for Women’s History Month, let’s write about some women with careers in science, technology, engineering and mathematics (STEM). Let’s get their stories back into the history books.
Why should we care about women’s stories? First of all, women have made significant contributions to these STEM fields and deserve recognition. Secondly, by sharing women’s stories we can help girls to enter scientific fields in the future by allowing them to sidestep common pratfalls, or at least see the roadblocks in a historical context. And finally, encouraging women of all races to participate in STEM enriches everyone.
Case Study
Let’s start with an example of how history repeats itself. My grandmother, Mabel Austin, went to Cornell University where she studied botany, horticulture and entomology. Her burning desire was to become a high school biology teacher. Upon graduation, she eagerly sought work. She had two things going against her, though. Mabel had the misfortune to graduate in the 1930’s during the Great Depression when jobs were scarce. She also had the misfortune of being a woman. As she reported to me later, “All the high schools wanted the biology teacher to double as the football coach.” During those times (and these as well), women were not accepted as football coaches. Mabel never taught high school biology.
Have things changed since the 1930’s? In the 1970’s, my male high school biology teacher also coached several sports. Fortunately he was also truly passionate about science and encouraged anyone who showed an interest or talent, regardless of gender.
How about in 2010? Although progress has been made, when I asked my neighbor if her brilliant daughter still wanted to be a marine biologist, she replied that her daughter’s high school biology teacher was also a coach. He told them the first day of class that he didn’t like teaching science. She hated the class so much she gave up her dream of marine biology and now she’s studying marketing.
How many women have been turned away from STEM through similar circumstances? How many discoveries and inventions have we squandered because of those losses?
(Note: We had some wonderful posts come in late, so I have made some additions and changes on April 1, 2010).
Women in Science and Technology
The Diversity in Science carnival starts with an extensive essay by Elizabeth Pain, Making Science and Family Fit about how Israeli structural biologist Michal Sharon manages to be a high profile scientist and a mother. Having a supportive husband who is willing to quit his job to allow her to follow her career is one critical element. Sharon wants to get the word out to young women, letting them know what they are capable of and what is possible.
Samantha Miller at EKG Classes gives us a reminder of 15 Female Scientists Who Changed the World. Some of the women are still household names, but many are not. How many do you recognize?
Chelsea Wald, editor of Under the Microscope: Where Women and Science Connect, brought Ada Lovelace Day to our attention, as well as the interesting and relevant posts which follow. Ada Lovelace Day is an international day of blogging to celebrate the achievements of women in technology and science. It was held on March 24, 2010. Who was Ada Lovelace? She was the first woman to write what could be considered to be computer software, although she was a mathematician as well. Her accomplishments inspired the following posts:
Being an entomologist, I am particularly interested in women entomologists. Debbie Ball has a list of seven Women Entomologists of the 19th and Early 20th Centuries at About.com. As she points out, women often were not allowed to publish their results under their own name, which makes it difficult to establish how much of a contribution they actually made. For example, some of Mary Ball’s discoveries were credited to her brother.
Women have participated in science and technology from the first. Telescope Women in History is a video that celebrates women astronomers from the earliest days of science.
For a fascinating look at women in science, visit the Smithsonian Institution Archives sampling of images of women scientists and engineers from around the world. This is the source of the photo below of botanist Wilmatte Porter Cockerell with biologist Theodore Dru Alison Cockerell standing with sunflowers. See how many women scientists from the past you can recognize at the Smithsonian site.
Agnes Scott College has an ongoing project recording the biographies of women mathematicians.The website also has information about the International Conference of Women Mathematicians (ICWM), which will take place in Hyderabad, India, on August 17 and 18, 2010.
Finally, perhaps it is time we as women began to write down our own stories. Chelsea Wald has invited women in science, technology, engineering and math to write a message to themselves at a younger age. See the results at Message 2 a younger me.
Let us know if you have posts about yourself or other women in STEM to share. Let’s keep telling the stories.
The April Carnival will be hosted at Rooted in the Earth. Since April is the month we celebrate earth day, arbor day, environmental awareness and all other earthy-eco-related things, the the theme for Diversity in Science Carnival will be “All Shades of Green” Diversity in Outdoor and Environmental Awareness. If you are interested in participating, please submit your posts via the carnival submission form.
If you have never seen a carnival by Jason, you will be surprised. His carnival posts are always so much more than a list of links.
