Today, they are aserious nuisance to gardenersand farmers across this continent.
However, not all metallic green or copper beetles are Japanese beetles.
They run in cycles; some years are almost devoid of beetles, while others are everywhere.
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Knowing when they are passing through each stage in your climate is important because control methods differ.
Egg
The mature beetles lay small, oval, white eggs in the soil.
If moisture is sufficient, the eggs will absorb it and enlarge, becoming rounder as they do.
The Spruce / Jayme Burrows
Larvae
Larvae are the white grubsthat are so familiar (and damaging) in lawns.
Japanese beetle larvae have a V-shaped series of bristles on their underside.
Grubs will grow in length as they feed and mature.
The Spruce / Jayme Burrows
As the soil cools and the grubs mature, they move back down deeper into the soil for winter.
Pupae
The pupae stage is when the grub starts to transform into a beetle.
Japanese beetle pupae start cream-colored and age to reddish-brown.
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As the soil warms, the larvae burrow toward the surface to change into beetles.
The pupating stage lasts about two weeks.
Adult Beetles
Adult beetles are less than 1/2-inch long and have shiny, metallic green shells.
The Spruce / Sanja Kostic
Depending on your area, adults emerge from the ground between May and June.
When the first beetles emerge, they immediately look for suitable plants and feed.
They also send out an odor known as a congregation pheromoneto signal later emerging beetles where to go.
The Spruce / Jayme Burrows
Mating starts soon after.
By the end of the season, each female Japanese beetle can lay about 50 eggs.
They live for about 30 to 50 days as adults.
The Spruce / K. Dave
Adult beetles will appear the following year if this cycle isn’t broken.
It’s impossible to entirely get rid of Japanese beetles.
More will fly in as the current group is killed.
The Spruce / Steven Merkel
And there aren’t many natural controls for adult Japanese beetles.
Controlling this pest will require you to use one or several hands-on methods.
Warning
A word of caution about pheromone beetle traps: They attract beetles.
The Spruce / Jayme Burrows
You might attract more beetles to your yard than before.
But you will need to do this every few days for the month.
Other methods include physical barrier controls, organic methods, and chemical pesticides.
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Chemical pesticides can kill other beneficial insects likeladybugs, bees, and butterflies.
Make Insecticidal Soap
Insecticidal soap is a mixture of water and the potassium salts of fatty acids.
Use a pureliquid Castile soap.
Do not use the soap solution if you notice spotting, wrinkling, or browning on leaves.
Spray Insecticidal Soap on Insects
Concentrate the spray directly on the insect and not the plant.
This is a relatively safe chemical pesticide.
They can be used in tandem and applied at the same time.
Non-organic farmers have a long list of broad-spectrum and selective chemical-based pesticides.
Neem oil is effective against Japanese beetles.
Japanese beetles in yards and gardens.
University of Minnesota Extension.
Using pesticides safely and correctly.
Insect Control: Soaps and Detergents.
West Virginia Extension Service.
Organic management options for the Japanese beetle at home gardens.
Integrated Pest Management University of Missouri.
Colorado State University Extension.
