Cotesia Species
Braconid Wasps

Hemileuca eglanterina larva and Cotesia species cocoons,
courtesy of Richard Wasson.

I (Bill Oehlke) think that the Cotesia cocoons that are depicted in the specimen above are probably those of Cotesia electrae which frequently attacks Hemileuca species.

Richard writes, "Hello Bill,

"On the 13th of June 2009, I collected eight Hemileuca eglanterina larvae on a ranch in Sonoma County, California. Two weeks prior I collected over fifty H. eglanterina on that ranch in the same area. During the trip of the 13th I found 3 caterpillars that were full of small white cocoons on their bodies.

I killed the caterpillars and made sure the cocoons were destroyed. About the 14th of June I found a caterpillar in my rearing cage that was full of cocoons. I found another one a few days later. I placed these caterpillars in a glass jar and waited till the cocoons emerged.

On the 26th of June I found a bunch of small wasps in the jar. I posted this picture on “BugGuide”, hoping to get help identifying them. I got the following feedback from “BugGuide”:

“Braconidae: Microgastrinae... There are numerous braconid subfamilies that prey on caterpillars. Although the wing venation is a critical element to confirm an ID here, this wasp does resemble adult members of the Microgastrinae which live exclusively off of Lepidoptera larvae, so I would place it there for now. …….”

Cotesia electrae adult, courtesy of Richard Wasson.

"I pinned one of the caterpillars with the wasps.

"If you like, I will send the full size pictures. I will search my pictures I believe I have few more pictures.

"Of the 50+ caterpillars collected on 4 June only about 3 ended up with parasites. On the 13 June collecting at the same place I only collected 8 caterpillars and 2 of them came up infected. So about 6% infected on the June 4 date and 25% on the 13 June. It seems that the wasps were just getting started about June 1 and by mid June they were out in force.

"Two years ago while collecting on the west face of Mt. Shasta I found literally millions of California Tortoiseshell chrysalis and larva. I brought back a couple branches that had 15 to 20 chrysalises on them. Two chrysalises emerged and a few days later I noted small wasps in the cage. I started by opening one chrysalis that had 60+ small wasps almost ready to emerge in it. I then opened up the rest of the chrysalises and they all were full of wasps. They averaged about 60 per chrysalis. Remembering how many caterpillars I saw and to think of 95% being infected with 60+ wasps, well the number of little wasps must be incredible."

There are many species in the Cotesia genus of parasitoid wasps.

Adult females have an ovipositor that can penetrate the skin of early instar larvae. Often large numbers of tiny eggs are inserted under the larval skin, and emergent wasp larvae feed internally on the lymph and fatty tissues. At maturity, the wasp larvae eat their way out and spin elongate silken cocoons, attached to the back and sides of the caterpillar.

Cotesia electrae (Viereck, 1912), commonly known as the Electra Braconid Wasp, lives in many diverse habitats including grassland prairies, arid deserts, oak/pine forests, and riparian zones. This species attacks virtually all species of Agapema, Hemileuca, and Coloradia in western North America, especially in the southwestern United States.

Infected larvae feed and often develop to normal size with the wasp larvae making their exit when the host larvae appear mature. Unfortunately, parasitism is often very high among found larvae, and a collector can receive a nasty surprise after rearing found larvae to near maturity.

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