Stink Bug Egg Parasitoids
Blake Layton (Mississippi State University) and Scott Stewart (University of Tennessee), Department of Entomology and Plant Pathology
If it weren’t for egg parasitoids, stink bug populations would be a lot higher than they are each year. Stink bugs lay their eggs in masses, and there are several species of very small parasitic wasps that take advantage of this by searching for stink bug egg masses and laying their own eggs inside the individual stink bug eggs. These little wasps are so small that they usually go undetected, but if you approach a newly deposited stink bug egg mass carefully and look closely, you can often see a very small gnat-like wasp lurking nearby. These wasps belong to the Scelionidae, a family that contains a very large number of species of parasitic wasps. Members of this family also attack the eggs of many caterpillar pests and other insects. There are several different species of these stink bug egg parasites. Some are quite host specific, attacking only one species of stink bug or a few closely related species. Others may have a most favored species, but will also attack others. Collectively, these stink bug egg parasites are probably the most important natural enemies of stink bugs. In one Louisiana study, levels of egg parasitism often were as high as 30 to 50%, and one California study reported parasitism levels as high as 87%.
Adults of these stink bug egg parasites can live from 2 to 6 weeks, and may parasitize from 30 to 300 stink bug eggs. Parasitized eggs turn black within a few days, and, depending on species and temperature, the adult parasites emerge within 8 to 20 days. Normally, only one parasitoid develops within each parasitized egg.
The eggs of all of the common species of stink bugs are subject to attack by at least one species of these stink bug egg parasites. The major parasite of the southern green stink bug is Trissolcus basalis, but this parasite will attack the eggs of other stink bugs when southern green stink bug eggs are lacking. Telenomus podisi is the most common egg parasite of brown stink bugs, but there are other species that also attack brown stink bugs. It is not uncommon to collect stink bug egg masses that have been attacked by more than one species of egg parasitoid.
There are several different species that attack the eggs of the beneficial spined soldier bug. One of these, Telenomus calvus, has a rather unusual behavior. In order to assure that it is present when the spined soldier bug female lays her eggs, this small wasp actually searches for female soldier bugs and then simply rides on their backs until the eggs are laid. Then it hops off and parasitizes the newly laid soldier bug eggs. At least one species of tropical stink bug has adopted the habit of sitting on its egg mass until it hatches in order to protect the eggs from being parasitized. Eggs around the outer edge of the mass still get parasitized, but this behavior does help protect the eggs located on the inside of the mass.