Trying to Understand Aphids

I know a little about the life cycles of aphids.  I know enough to know I don’t know very much.  I was walking around with my camera today and I came upon about three plants of giant ragweed that were covered with aphids–at least several inches of stem were.  We have ragweed all over the place, and none of the other plants seem affected.

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Aphids have many generations each season–somewhere between ten and twenty generations for some species.  There are winged forms and wingless forms which give birth to live young through parthenogenesis.

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There is one popping out right there.

Sometimes you can find mummies–aphids which have been infected with some internal parasite and have just a shell, with the fly or wasp larva developing inside.  This group had a couple, but mostly had apparently healthy live aphids.

Sometimes they are tended by ants, but these weren’t.

A few feet away was a wild lettuce plant with a number of apparently dead or parasitized aphids, looking like the same species.

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Why did they succeed on the ragweed and not on the wild lettuce?  Will there be more parasites in a few days?  If they reproduce so rapidly, why don’t they take over every plant?

 

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About the roused bear

Nature photographer from central Iowa.
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2 Responses to Trying to Understand Aphids

  1. theresagreen says:

    Fascinating post and some good close-ups. I know nothing about aphids so found this very interesting; I had no idea that there was anything else around that would parasitise them. Perhaps they choose ragweed for the same reason the cinnabar moth larvae do- they take in the noxious chemicals from the plant so predators find them unpalatable. May account for the aphid’s apparent success on that plant?

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