More Misfortune for Monarchs

December 13, 2016

Aphids2 (1)

Photographer: Rob Sheridan
Summary Author: Rob Sheridan

The monarch butterfly (Danaus plexippus) is particularly famous for two things: its multi-generational annual migration from Canada to Mexico and its reliance on milkweed as sustenance. The U.S. Fish and Wildlife Service is now evaluating monarchs for placement on the endangered species list because monarch numbers have plummeted by 80 percent in recent years. This dramatic population decline is thought to be largely caused by the herbicide-induced reduction of milkweeds in the agricultural midwestern United States.

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 taken on October 21, 2016.

Photo Details: Camera: NIKON COOLPIX P900; Focal Length: 18.7mm (35mm equivalent: 105mm); Aperture: ƒ/4.0; Exposure Time: 0.017 s (1/60); ISO equiv: 100; Software: Microsoft Windows Photo Viewer 6.1.7600.16385.