|The ensign wasp, Evania appendigaster may be one of the |
oddest looking insects in pest control. Its name comes from
the flag-shaped abdomen that it waves while searching
for its cockroach prey.
Ensign wasps are cockroach egg parasites. They are experts at locating cockroach egg cases (oothecae). According to one account, when the female ensign wasp encounters a cockroach egg case, she first taps it with her antennae, presumably to confirm that it is an acceptable host for her egg. Then she lies down beside it (I have never heard of an insect voluntarily lying on its side before!) and braces her legs against the ootheca. After much labor she inserts her slender ovipositor into the tough ootheca and lays a single egg. After hatching, the wasp larva matures while feeding on the dozen or more cockroach eggs inside each ootheca. No cockroaches will hatch from an egg case that has been parasitized by an ensign wasp.
The name ensign wasp comes from the unique, stalked abdomen. Shaped like a sailor's signal flag, the wasp frequently waves her abdomen up and down while stalking her prey as if to say, "Here I am! Look out cockroaches!"
|The oothecae of American cockroaches are glued in out of|
the way locations in walls, attics and other places. A single
egg inserted by an ensign wasp inside the ootheca will prevent
hatching. Bugwood photo by Gary Alpert, Harvard Univ.
Nevertheless if you or your customer are seeing these wasps on a regular basis, it might mean there are more cockroaches around than you suspect. Check the crawl space, attic and utility areas. Make sure that p-traps in the floor drains are being filled with water on a regular basis. Consider setting out sticky traps and baiting suspected harborage areas such as garages, attics, pantries or utility rooms.
If you are looking for more information to provide your customers about cockroach control, check out the Extension fact sheet Cockroaches and Their Control.