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Friday, September 11, 2015

What are these bugs in my garden?

“A few weeks ago, I noticed a lot of strange insects on my magnolia tree. They were black in color with antennae and wings folded over the top of their bodies. When you looked at them from the side, they have a kind of pointed teardrop shape, but from above they looked very narrow. They were clustered in pretty large circular groups all over the bark and branches of my tree. I sprayed them with a hose and they scattered. Do you know what they were?”

We brought out Insects by George C. McGavin and The National Audubon Society Field Guide to Insects and Spiders. First we looked up termites, which is what our patron thought their insects were. However, they turned out to be the wrong shape, their antennae were too short, and their wings were too pale. We flipped through the color plates at the beginning of the Audubon Society Field Guide, and that’s where our patron recognized their mystery insect as a type of aphid.

We were surprised, as we’re used to thinking of aphids as tiny, plump, wingless bugs, usually green in color. (These wingless aphids are sometimes called “ant-cows” because ants will “milk” them for the honeydew they secrete.) Winged female aphids will migrate to a new host plant and establish a new colony through a kind of asexual reproduction called parthenogenesis. (Eggs produced this way can develop into young without being fertilized.) The aphids produce several wingless generations this way, eventually producing more winged female aphids, which then fly back to their original host plant to mate with males and lay fertilized eggs.

According to Rodale’s Vegetable Garden Problem Solver by Fern Marshall Bradley, the best way to deal with aphids is to lure beneficial insects, like ladybugs and lacewings, to the aphid-infested plants. In the meantime, hosing the aphids off every three or so days for two weeks should help keep them at bay.

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