This aphid has been parasitized by a tiny parasitoid wasp. Parasitoid wasps lay eggs in a host, like this aphid. As the egg hatches and the larva develops, it causes the aphid to swell, making it appear bloated. When the larva matures, it bores out of the host, leaving a hole in the abdomen, as seen above. The bloated body that the wasp leaves behind is known as an “aphid mummy.” These beneficial wasps can be attracted to fields and gardens by planting a variety of wildflowers, especially sweet alyssum, dill, cilantro, parsley, buckwheat, etc. Click here to learn more.
For more information on Natural Enemies, see HGIC 2820, Natural Enemies: Predators and Parasitoids and Natural Enemies: Parasitic Wasp.