A new scourge is attacking the milkweed plants that are essential to the survival of Monarchs:
But the menaced monarchs have another problem, the destructive oleander aphid (Aphis nerii). This bright, yellow insect, introduced from the Mediterranean area along with the oleander plant, has found milkweed to be an attractive food source. They form large colonies on milkweed stems and leaves that aspirate sap from the plants’ nutrient-transporting phloem, stunting or killing their host before it can provide sustenance for migrating monarchs and their larvae. This photo shows an aggressive colony of oleander aphids feeding on a first-year common milkweed (Asclepias syriaca) near the coast of Massachusetts. For cultivators of monarch milkweed gardens, non-toxic insecticidal soaps are effective against the oleander aphid. However, the threatened monarch will likely need more help in order to survive.Photo credit Rob Sheridan, via the Earth Science Picture of the Day, with a tip of the blogging hat to reader David Laidlaw for bringing this to my attention.
Here in central Ohio I have a few native milkweed on the property, and large patches of Asclepias tuberosa all over the place - these aphids can destroy the orange butterfly weed in a day or so, it's amazing, but so far they mostly ignore my native milkweed. Somewhere I have a picture of a single a. Tuberosa with 11 monarch caterpillars on it, I think it was in 2014; the last 2 summers the aphids have done so much damage to my plants that I have seen virtually no caterpillars, except on my native milkweed. I will stock up on insecticidal soap for next summer, for sure.
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