The Japanese beetle, Popillia japonica, a member of the scarab beetle family, is the adult stage of the white grubs found in your lawn. They were first introduced to the United States via New Jersey from Japan in 1916, where they were not considered a pest. In some parts of the country there are protozoans in the soil which help in controlling the larval stage of Japanese beetles. These destructive pests do have a couple of natural controlling agents; the fly Istocheta aldrichi and the tiphid wasp Tiphia vernalis, however, neither can exert complete control over infestations.
Right on schedule, the beetles have been active since early July and females will have already laid eggs or will do so very soon. Japanese beetles can be very destructive pests of both turf grass and ornamental plants. Grubs will target the roots of grass while adults enjoy defoliating over 300 species of plants. Japanese beetle adults are pretty easily identifiable; they are approximately 3/8 inches long with a metallic green head and metallic tan wings. Grubs can be identified by their characteristic “C” shape along with the distinctive hair patterns on their hind ends which form a small “V” shape just below the anal slit.
Life Cycle Contrivance
Adult Japanese beetles will emerge from the soil in early July and begin feeding, mating and laying eggs. Intensive feeding activity will be seen for the next 6 to 8 weeks when beetles eventually begin dying off. Beetles can live up to 60 days and females can lay approximately 60 eggs over this time span. They like to feed on the top foliage of plants, in full sun and then continue downward consuming as they proceed. Damaged vegetation emits an odor which attracts more beetles and, in addition to pheromones secreted by adults, can result in large aggregations of beetles. When dusk arrives the pheromone ceases to be emitted and females will land on turf to lay eggs, burrowing 2 to 3 inches into the soil.
If you already have a lawn program in place or you have concerns about grubs and/or Japanese beetles talk to your arborist about adding grub control to your program. If you are already seeing Japanese beetles feeding on your ornamental plants, contact your arborist as soon as you possible and they will help establish control and develop a plan for aiding your plants in recovery. Unfortunately, Japanese beetles feed on many popular landscape plants, including, but not limited to; American chestnut, American elm, American linden, American mountain ash, apple, birch, black cherry, cherry, flowering crabapple, grapes, hollyhock, horse chestnut, Norway Maple, plum, roses and walnut. While they tend to avoid defoliating; American elder, arborvitae, black oak, box elder, common lilac, hemlock, holly, juniper, pine, red maple, silver maple, spruce, white ash, white oak, white poplar, euonymous, fir, green ash, red oak, rhododendron, scarlet oak and yew. If there is a Japanese beetle problem in your area consider some of the more rarely targeted plants as additions to your landscape, or if possible, replace some highly targeted plants. These are not hard and fast lists, there are always exceptions to the rule, if you have any concern at all, speak with your arborist.