Green June beetle (Figure 1) flight has begun across Kentucky. They are similar to, and at the same time different from, Japanese beetles.
What They Have In Common
Both species are good fliers and congregate in large numbers when feeding. Also, each has one generation each year and their larval stages are white grubs that develop in soil.
Females of both species fly low over the turf during July and August as they look for suitable areas to lay eggs. These beetles will land and enter the soil to lay eggs where conditions are right for them. Adequate soil moisture is vital because eggs of both must absorb a significant amount of water in order to hatch. That should be relatively easy this summer because of the amount of rainfall that has fallen.
Different Feeding Habits
Green June beetle grubs feed on organic matter, while Japanese beetle grubs feed on grass roots. Feeding by Japanese beetle grubs can result in dead patches in turfgrass; green June beetle grubs will not do this.
While Japanese beetles feed extensively on leaf tissue, green June beetles eat soft sugary foods: ripe and over-ripened fruits, corn tassels and silks, tree sap, and honeydew. Feeding causes fermentation and production of volatile organic compounds that attract other individuals. Information on green June beetle management on grapes is available in the publication, Green June Beetles on Grapes (ENTFACT-227).
Green June Bug Grubs Have a Natural Enemy
When green June beetles show up, the blue winged wasp is not far behind. This distinctive 1/2-inch long wasp with blue-black wings has a reddish tail and two yellow bars near the end of its abdomen (Figure 2). It is a natural enemy of green June beetle grubs.
These wasps cruise over grassy areas in search of grubs. They will enter the soil and burrow to find the beetle larva, sting it, and then lay an egg. The wasp larva uses the grub for food and spends the winter in a cocoon within the host, emerging the following year. The wasps are not aggressive and do not pose a threat. Nectar provides them with an energy source that allows them to search for prey so they are commonly seen on flowers.
By Lee Townsend, Extension Entomologist