Saturday, July 11, 2009

All about aphids...

...is not what you're going to learn from this single post, but they are fascinating creatures. I'm not an entomologist, so the following information comes from Stephen A. Marshall's Insects: Their Natural History and Diversity, a phenomenally learned yet accessible and beautiful book.

According to Dr. Marshall, "Even in winter you can find little black aphid eggs on apple and other trees, usually near buds. In spring these eggs will hatch into wingless females, which will develop rapidly and give birth to more wingless females without bothering with sex or eggs. Later in the season, as things become a bit more crowded, winged females will appear and, depending on the species, move to other plants.... In temperate regions many aphids produce wingless sexual females in late fall; these mate with the winged males to produce eggs that withstand the winter and hatch to wingless females in the spring."


There are apparently more than 1,300 species of aphids in North America. I don't have the resources to identify the species here, but if anyone who does know would like to comment, I'd be grateful. The pink ones were found on a cilantro plant. They "do the wave" continually--one of them will give a little shimmy, then they all do it in chorus.


I believe these black aphids may be black willow aphids.


What the ant is doing is sucking honeydew from the backside of one aphid. "Like most other homopterans, aphids pierce the phloem tissue of plants, and feed by pumping huge amounts of sugar-rich and nitrogen-poor sap through their bodies. Homopterans must suck enormous quantities of sap to obtain sufficient protein, excreting the excess sugary fluid as copious quantities of honeydew. Far from the mere waste product it appears to be at first, honeydew is like a currency with which aphids pay for services provided by other organisms." The honeydew gets secreted in large clear drops. Later in the summer, it's not uncommon to find honeydew literally splashed all over the foliage under an aphid colony, and a variety of insects, including flies and wasps, feeding on it.


The green ones again, I'm not going to guess the species of, but they're on a spirea bush and they return every year, possibly, as Dr. Marshall suggests, placed there by the ants that care for and protect them (and which also may "take [their eggs] home for the winter, moving the eggs around the ant nest to maintain them at optimum temperature and humidity. In the spring, newly hatched aphids are solicitously placed on the roots of weeds, where the first generations of aphids feed...").



The two little "hairs" sticking out of their backs are called cornicles, and they "secrete a sticky substance that deters predators and may even trap and kill would-be parasitoids....The same chemicals may also attract ants to the defence of the threatened aphid..."







It doesn't always work, though.

One benefit that veganic gardening (which here means essentially that I no longer dig the soil, and that I leave the plant foliage in the garden after it has died back in the fall at least until the following spring) has, is that it provides undisturbed homes for predators. I used to have a lot of trouble with aphids, horrific infestations that used to maim and kill perennials. The aphid eggs would overwinter on the plants themselves, but the predators couldn't.

There are still aphids in my garden, as these images show, but their populations haven't become threatening in any of the four summers since I stopped digging.
And, as you can see, they fill an important role in the garden mini-ecosystem and provide me with hours of enthralling entertainment.

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