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June Beetle or Emerald Ash Borer?

How to tell the difference between the two insects

By: Sandy Feather 2009
Penn State Extension


Ever since emerald ash borers were discovered in late June just north of Pittsburgh, PA in Cranberry Township, people have been understandably nervous about shiny green insects. The green June beetle has been generating phone calls to my office this past week, and I thought it would be helpful to write an article to help distinguish green June beetle from emerald ash borer.

Green June beetles (Cotinis nitida) are one of the scarab beetles whose larvae are known as white grubs, which can be destructive pests of lawns. Adult green June beetles can be intimidating because they are large - three-quarters to one inch long - and they make a loud buzzing noise as they fly. Their backs are dull green, often with tan stripes running down their sides, and shiny green or gold underneath.


Basic Identification Method

The overall impression is that of a "shiny green insect." Green June beetle grubs are cream-colored with brown heads. They range in size from three-eighths of an inch to an inch-and-a-half long, depending on maturity, and have three pairs of stubby legs. They have the unusual characteristic of crawling on their backs to move since those tiny legs cannot support their large bodies adequately.

japanese beetle
Japanese Beetle

 


Life Cycle of Grubs

We have one generation a year in our area. They overwinter as mature grubs deep in the soil. As temperatures warm in spring, they migrate back to the soil surface where they feed briefly on thatch, soil, and grass roots before pupating. Pupation takes 16 - 18 days, and then they hatch out as adult beetles. That occurred the week of July 9 in the Pittsburgh area, if I can judge by the calls made to our office. Scarab beetles typically hatch in groups, and they come up out of the soil in a mass of wriggling beetles that looks like something out of a sci-fi movie!


What Scarab Beetles eat

Adults often feed on ripening fruit, and females are attracted to piles of bark, grass clippings, manure and compost as ideal places to lay their eggs. Lawn areas that are fertilized with organic fertilizers, sewage sludge and/or compost are more attractive to egg-laying females than those treated with conventional fertilizers. They may also be attracted to lawns with heavy thatch layers. Grubs hatch in 10 -15 days.


Green June Beetle foods

Green June beetle grubs feed primarily on decaying organic matter (thatch), although they can destroy enough grass roots to damage lawns. Mature larvae burrow to the soil surface at night and often graze on the grass. The burrowing activity can be the most damaging, as they build mounds two to three inches in diameter, and the burrows can be six to twelve inches deep.


Insecticidal Controls

Preventative controls such as Bayer Advanced Season Long Grub Control (imidacloprid) or Spectracide Grub Stop Once & Done (halofenozide) should be applied before green June beetle eggs hatch. Once you see the damage - and the grubs - Bayer Advanced 24-hour Grub Killer Plus (Dylox) is a better choice. Overwintered, mature grubs that are active in spring are more difficult to control.

If the adults are active in your yard, monitor your lawn for signs of damage. Where you see thinning or browning, dig up a square foot to check for grubs. Five or more green June beetle grubs per square foot warrants treatment. An otherwise healthy lawn can tolerate fewer.

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