On one of my first days at Cornell, I stumbled upon an interesting scene. A pink-spotted ladybeetle (Coleomegilla maculata) stood motionless on a lamppost. Underneath the beetle was a brown fuzzy object, with strands wrapped around the beetle’s feet. What was going on here?
This scene was the result of the handiwork of a fascinating parasitoid wasp, Dinocampus coccinellae. Like many parasitic wasps, it is tiny, only a few millimeters long. The species is mostly parthenogenic, with occasional males found. The female lays an egg in a lady beetle, commonly either C. maculata or the 7-spotted lady beetle, Coccinella septempunctata). When the wasp larva hatches out, it first feeds with the help of “trophic cells” that absorb nutrients directly from the host. Later, the larva feeds directly on the lady beetle. Once the larva has finished development, it severs the nerves in the lady beetle’s legs and then pupates underneath the beetle. This leaves the beetle alive, but immobilized, essentially turning it into a zombie. The helpless beetle can only twitch and reflex bleed from its joints. The fascinating thing is that since lady beetles are poisonous to most predators, the presence of the stricken beetle above the wasp larva’s cocoon affords protection for the wasp. After a few days, the adult wasp emerges and flies off to start the cycle again. Interestingly, about 25% of parasitized lady beetles recover from this situation, highly unusual for most hosts of parasitoid wasps. Dinocampus is a concern in the UK because the rate of parasitism of lady beetles is very high. Because lady beetles are important in controlling aphids in gardens, this represents a real threat to gardeners. However in most places where the wasp occurs, it is simply an interesting creature going about its business.
I collected the lady beetle and wasp cocoon, and in 4 days the wasp emerged. It is a pretty red and black animal with greenish blue eyes. A very cool insect to see. Watch for an unmoving lady beetle and perhaps you will find one of these interesting wasps yourself.
Species Dinocampus coccinellae – BugGuide.net. (2009, November 20). Retrieved from http://bugguide.net/node/view/157232
Bruce, A. Parasitoid Wasp threatens Scottish Seven Spot Ladybird. Retrieved from http://www.microscopy-uk.org.uk/mag/indexmag.html?http://www.microscopy-uk.org.uk/mag/art98/ladybird.html
Dinocampus coccinellae. (2015, February 18). Retrieved from https://en.wikipedia.org/wiki/Dinocampus_coccinellae