Issue 15, August 28, 2009

Scoliid Wasp

Scoliid wasps, family Scoliidae, feed as parasitoids on the larvae of green June beetles. With higher numbers of these beetles in many areas of Illinois this summer, we are now getting reports of large numbers of scoliid wasps. These are one inch long black wasps with the posterior portion of the abdomen being orange with a couple of yellow spots. These wasps cruise over turf areas in figure 8 patterns searching for locations to lay their eggs. They tend to fly a foot or so above the grass, being very noticeable.

Once located, the wasps crawl down into the burrows of the green June beetle grubs. Once it locates a beetle grub, it stings it to paralyze it, and lays an egg on the underside of the grub. This egg hatches into a legless larva that feeds on the paralyzed, but still living, beetle grub. When fully grown, the larva spins a cocoon, pupates, and emerges as an adult wasp during the next growing season.

Although fearsome in appearance, the adult wasps are unlikely to sting unless grabbed or stepped on while barefoot. With these wasps in almost constant motion, it is difficult to find one at rest where it could be grabbed or stepped upon. Thus, treatment is normally not recommended. However, applying a grub control should indirectly cause the adult wasps to leave due to a lack of hosts to attack.--Phil Nixon

Phil Nixon

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