[Pollinator] Habitat Tip: Controlling Aphids on Milkweed - let the wasps work instead

[Clement Kent]

While I appreciate Peter Berthelsen's use of plain soap, I've been watching
my milkweeds for natural enemies of oleander aphid. There weren't many of
these enemies 8 years ago when I first started noticing big infestations on
milkweeds, but now (in my area, at least) there are some. I'm raising some
60 swamp milkweeds for planting out in various pollinator gardens, and the
usual infestation started a little over a month ago. Within 2 weeks,
though, some of the aphids were turning black, and now the first plant
infested is almost aphid-free.

Watching carefully one morning, I saw a small parasitoid wasp flying to
different milkweed leaves and stems. When it found oleander aphids, its
antennae started tapping them busily. I didn't have time to see it laying
eggs into the aphids, but I'm betting that's why my infestation seems to be
controlled. Note that the aphids are not entirely eliminated but their
numbers are reduced to the point where they don't seem to be harming the
plants.

If you have badly infested specimen plants and no signs of natural enemies,
use soap if you must. But be aware that if you spray a monarch egg or
caterpillar, you may kill it.

Clement Kent
Toronto, Canada
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