Lysiphlebus testaceipes (aphid parasitoid)
Blake Layton (Mississippi State University) and Scott Stewart (University of Tennessee), Department of Entomology and Plant Pathology
This small parasitic wasp does not really have a common name, but it is often referred to as the “aphid wasp”. Next to the “aphid fungus” (Neozygites fresenii), it is probably the most important biological control agent of cotton aphids. Levels of parasitism can exceed 70% in some situations. It is likely that this parasite would play an even greater role in aphid population suppression if it weren’t for the fungal disease eliminating aphids first. On the other hand, there are indications that the parasite helps spread the fungal spores from one aphid to another, thus hastening the development of the disease epizootic.
Description and Biology:
The adult is a very small black wasp, approximately the size of a winged cotton aphid but more slender. Females can be seen crawling about on the undersurface of cotton leaves in search of aphids to parasitize. When a suitable aphid is found, the wasp curls its abdomen forward between its legs and ‘stings’ or lays an egg in the unfortunate host. An individual adult can parasitize up to 100 aphids during its brief life. Eggs hatch in 2-3 days, and the larval parasite begins feeding inside its aphid host before ultimately killing it. The larval stage lasts about a week, and the pupal stage, which takes place inside the body of the host aphid, takes an additional 4-5 days. Thus, the complete life cycle takes roughly two weeks.
During the early stages of parasitism, parasitized aphids appear normal. As the developing parasitic larva grows larger, it eventually kills the aphid, causing it to swell and turn beige to tan in color. These “aphid mummies” are readily recognized and provide an easily observed indication of parasite activity. However, it is important to keep in mind that the actual level of parasitism is considerably higher than would be indicated by counting the percent of aphid mummies. Once the percentage of mummified aphids reaches 10-20%, it’s a good bet that most of the aphids present on a leaf have been parasitized. Upon reaching the adult stage, the wasp cuts a small circular hole near the back end of the aphid, emerges, and begins searching for aphids into which to lay its eggs. Lysiphlebus overwinters inside its aphid host as a larva or pupa, and mummified aphids can be found throughout the year.
For a parasitoid, Lysiphlebus has a relatively wide host range, attacking a number of economically important aphid species. Cotton aphids and greenbugs, an important pest of wheat and sorghum, are two of the more important aphids that are parasitized by this wasp, but it can be found attacking many other aphids.