67 genera worldwide, 38 (with over 500 spp.) north of Mexico(1)(2)
Endoparasitoids. Examples of cocoons
They are koinobiont
endoparasitoids; hosts are mostly Lepidoptera, Symphyta and a few attack Coleoptera. (Koinobionts allow for further host development to occur before the host is destroyed. Koinobiont endoparasitism allows the parasitoid to oviposit inside conspicuous hosts, while using the host's pupation concealment to secure continued development.)
Females of this subfamily inject POLYDNAVIRUSES into the host during oviposition. These virus particles compromise the host immune system, protecting the parasitoid progeny. Click here
for more information on this fascinating example of mutualism.
"Gauld (1984) writes about certain campoplegines that emerge from the host before it reaches the final instar: 'the parasite generally spins a characteristic greyish or blotched cocoon attached to the host’s food plant. In such a situation the cocoon is particularly vulnerable to being secondarily parasitized by small phygaduontines and pimplines. Consequently campoplegines have adopted a number of ruses to avoid parasites. Some species (e.g. Charops) suspend their cocoon from the plant by a long thread and many also have black and white blotched cocoons that resemble bird droppings. Some other species construct a false cocoon above the real one whilst the mature larvae of a few genera (e.g. Spudastica and some Phobocampe) are able to cause their cocoons to jump.'" - quoted from correspondence with Dr. Andrew Bennett, Curator of Hymenoptera, Canadian National Collection of Insects
A further note from Andrew Bennett, regarding species level identification of Campopleginae: "most genera have no keys to species, and so the only way to identify specimens is with reference to type specimens... some genera have more than 100 described Nearctic species."
Gauld, I.D. 1984. An introduction to the Ichneumonidae of Australia. British Museum (Natural History) Publication 895. 413 pp.
Shaw, M.R. & R.R. Askew. 1983. Parasites. Chapter 2 in Heath, J (Editor): The Moths and Butterflies of Great Britain and Ireland. Volume 1 Micropterigidae - Heliozelidae. Harley Books. pp.24-56 [many photos of cocoons]