Today I am showcasing an example of biological pest control that I came across in my own neighborhood in late April of this year. The image below shows a bronzed cutworm moth larvae (Nephelodes minians) in the Family Noctuidae that has been parasitized by a Braconid wasp in the genus Cotesia. This is a very species-rich genus of parasitoids, but there is a fair chance of this species being C. marginiventris. Thanks very much to Alex Soohoo-Hui for his assistance in narrowing down the identification of this minute wasp.
The bronzed cutworm is a very common moth that feeds on various grasses, including crops like maize and other cereals as well as turf grasses. I consistently find these cats or their chrysalis whenever I dig a new hole in the yard.
After the wasp deposits her eggs on the host, the wasp larvae feed on the caterpillar internally, being careful not to do much damage to vital organs. The host will never survive, but the parasitoids must ensure that it stays alive long enough for the brood to reach maturity. Often, the caterpillar will still be alive when the wasp larvae emerge and begin to spin their cocoons and will defend itself and its parasites from potential predators.
In this case, the caterpillar seemed dead. I collected it and took it home with hopes of rearing out the tiny wasps to photograph and identify. In about four days, I came home to find 15-20 adult wasps had emerged.
The adult wasps are extremely tiny, measuring 2-3 mm. In order to have a chance at getting photographs, I placed their enclosure into the refrigerator for a minute or two. The wasps in the accompanying images might appear dead, but they perked up within a couple of minutes. After getting my photographs, I released the brood into my backyard to continue their pest control services.
A couple more looks at this diminutive but effective parasitoid.
A Thousand Acres of Silphiums 