Pest description These small (males: 2 to 3 mm, females: 3 to 4 mm) wasps are metallic dark green to black parasitoids with red eyes that enter bee nests through cracks. Female wasps typically deposit about 10 eggs into a developing host BOB pre-pupa or pupa; a wasp may lay eggs in several host pupae. Wasp larvae feed internally in the BOB pupae and pupate within the dead bee. Development of wasps from egg to mature adult takes about one month, at which time adults emerge through round holes chewed in the host body wall. Mature wasp larvae overwinter in the cocoons of bees. Infestation levels may build up over the summer and may reach harmful levels if not managed well.
Management Chalcid adults become active toward the end of the BOB nesting period and therefore it is important to remove nesting materials soon before or after nesting activities have ended to minimize initial infestation. Mosquito screen (with mesh < 1 mm) can be used to isolate and maintain chalcid-free nests. Physical barriers, such as double-sided tape, may be used in the back and entrance of the nests and help reduce accessibility to wasps. Paper straws (with walls >1 mm) can be used as inserts in cardboard tubes and nesting blocks to minimize parasitism. In storage areas, adult wasps may be attracted to blacklights and drowned in a tray of baby oil or detergent-containing water.