Bill Cissel, Extension Agent – Integrated Pest Management; bcissel@udel.edu
Congratulations to Bob Leiby for correctly identifying the parasitized aphid in the photograph and for being selected to be entered into the end of season raffle for $100 not once but five times. Everyone else who guessed correctly will also have their name entered into the raffle. Click on the Guess the Pest logo to participate in this week’s Guess the Pest challenge!
The aphid in the photograph has been parasitized by a tiny wasp, about 1/10th inch in length. The adult female wasp, referred to as a parasitoid, lays an egg in the aphid. When the egg hatches, the tiny white parasitoid larva develops inside the aphid which eventually kills the aphid. Once the parasitoid larva finishes its development, it pupates, causing the aphid body to turn tan or black depending on the species of parasitoid. An aphid that has been parasitized is referred to as an aphid mummy.
Highly magnified image of a Braconid wasp (parasitic wasp).
Parasitic wasps and other beneficial insects play a major role in keeping aphid populations in check in many cropping systems. For example, in small grains during heading, a ratio of one beneficial insect (lady beetle larva, syrphid fly maggot, lacewing larva, damsel bug or parasitic wasp) per 50-100 aphids is often sufficient to achieve biological control. Because of this, if you have an aphid infestation, it is always important to also note beneficial insect activity.