I don’t know about you but part of my regular nighttime routine involves reading a good book at bedtime. This puts me in pretty good company as Bill Gates and Oprah Winfrey also do a little reading just before dozing off. During the past few weeks, these moments of mindfulness have been interrupted by a steady pelting of rather large scarab beetles attracted to the light from my bedroom window. Asiatic garden beetles are notorious for being attracted to light. These rascals are close kin to Japanese and Oriental beetles we visited in previous episodes. Like Japanese beetles, they are invaders from Asia first detected in New Jersey. Their discovery in the Garden State in 1921 followed the earlier discovery of Japanese beetles in 1916. Asiatic garden beetles now range from Canada to Florida and west to the Mississippi.
As adults, these scalawags are known to eat more than 100 species of ornamental plants, but they can also be important pests of vegetables, including corn. The misery they levy on our ornamental plants comes as they munch leaves and flowers of our trees and shrubs. Over the past week or so, great chunks of leaves and flowers vanished seemingly overnight from my sunflowers and butterfly bushes. Repetitive and thorough daytime plant inspections failed to reveal the perpetrators of this assault. However, a midnight’s visit to my butterfly bush revealed hordes of Asiatic garden beetles busily stripping away the foliage.
Like Japanese beetles, the six-legged larvae are soil dwellers shaped like the letter “C” which go by the name of white grubs. Gourmands of roots of a wide variety of weeds and herbaceous plants, they can be particularly damaging to cool-season grasses. Recorded densities can be as high as 100 per square foot and, not surprisingly, turf can be severely damaged at these levels of infestation. Adults wreak havoc on plants through July and into August, moving between feeding sites on plants to the soil where females dig into the earth and lay eggs. Each female lays roughly 60 eggs during her four-week lifespan. Eggs hatch from July through October and grubs consume the roots of plants before moving deeper into the earth with the approach of winter’s cold. With the return of warm temperatures in spring, grubs return to the root zone to feed and complete development. Pupae can be found in the upper six inches of soil during June and July, whence adults issue forth to visit their desolation on above ground portions of plants.
Asiatic garden beetles are very poor swimmers and brushing them into a container of soapy water put an end to their mischief. Floating row covers can exclude beetles from ornamental plants and may help prevent damage to vegetables. Applications of white grub-infecting nematodes may also prove useful in reducing populations of grubs in flower beds and turf. Several species of parasitic wasps attack white grubs with paralyzing stings and deposit their eggs on the grub. Upon hatching, these parasitic wasp larvae consume their hapless victim. Flowering plants such as goldenrods and bee-balms are magnets for adult wasps, which require nectar and pollen sources. I always have these in my flower beds to attract these highly beneficial wasps, part of Mother Nature’s hit squad that help mitigate pests like white grubs.
At this rate not much will be left of my plants once marauding Asiatic garden beetles arrive.
Adequate soil moisture is critical to the survival of eggs of Asiatic garden beetles and other members of their clan. Withholding irrigation from flower beds during times of adult feeding and egg-laying may encourage adults to lay eggs elsewhere. Drought may also reduce the survival of eggs and a dry July and August may translate into fewer beetles a year downstream. Unfortunately, with plentiful rain last year and again this spring and early summer, my money is on a bumper crop of Asiatic garden beetles and their relatives, including Japanese beetles, in 2020 in the Washington-metro region. So, if you hear something go bump in the night at your bedroom window and if your sunflower’s leaves are disappearing mysteriously, grab a flashlight a have a look for these midnight marauders.
The fantastic reference “Destructive Turfgrass Insects” by Dan Potter was used in preparation of this episode, as was the University of Florida website “Featured Creatures”- common name: the Asiatic garden beetle.