Scoliid Wasps
Scolia dubia Say, Scoliidae, HYMENOPTERA


DESCRIPTION

Adult -- The adult is over 20 to 25 mm long, with black antennae and a shiny black head, thorax and fore abdomen. Two yellow spots (one on each side of the abdomen) are sometimes very faint or absent. They may appear as a band across the abdomen when the wasp is flying. Behind the yellow spots, the abdomen is more brownish and the hairs on the body more noticeable. The wings are dark blue.

Larva -- The larva of Scolia dubia is a legless, white grub with a brown head. It appears hairless and has no eyes. The antennae, maxillary and labial palps are one-segmented. There is a slit-like silk gland on the labium.


BIOLOGY

Distribution -- Scoliid wasps (S. dubia in particular) range from New England to Florida and west to the Rocky Mountains. Other Scoliids are found throughout the tropics and temperate zones of the world.

The wasps are present in North Carolina from June to October; however, in the Raleigh area, they are most prevalent during the month of August.

Feeding Habits -- Green June beetle and Japanese beetle grubs seem to be the primary host of S. dubia.

Damage -- No damage has been reported from these wasps. Homeowners, however, are often needlessly alarmed by the attractive scoliid wasps which are often abundant in August and September. Although scoliid wasps are virtually harmless and are beneficial in their control of beetle grubs, their presence in large numbers may indicate a large population of beetle grubs.

Life History -- One of the most common scoliid wasps in North Carolina is S. dubia, often referred to as the blue-winged wasp. These beneficial wasps lay their eggs on soil-infesting white grubs such as the larvae of May and June beetles and green June beetles. The adults feed on the nectar and perhaps on the pollen of flowers. They do not sting people unless greatly aggravated or captured in the hands. They fly several centimeters (a few inches) above grub-infested soil in a more or less figure-eight pattern.

Female wasps work they way through the soil in search of grubs, burrowing their own tunnels or following those made by grubs. On locating a grub, she stings and paralyzes it. She may burrow 1.2 cm deeper to construct a cell around the host. Then she lays an egg on the outside of the grub. The parasitized larva provides a fresh food supply for the wasp larva. The stung grubs never recover. Many grubs are stung, but only a few eggs are laid. These wasps, therefore, are very important natural agents in the control of grubs in the soil.


CONTROL

Since these beneficial insects rarely, if ever, sting people no control measures are needed. Their presence, however, means there is a green June beetle, Japanese beetle or May beetle grub infestation that may be only partially controlled by these parasites. For recommended insecticides and rates, consult the stage agricultural extension service recommendations.