Chafers such as exotic invasive Asian garden beetles (top) and Oriental beetles (bottom) can mean big trouble for your ornamental plants.
Three weeks ago, we visited fireflies that are enjoying a spectacular year here in the DMV and in other states in our region. One reason for this renaissance may be due to the benign winter and mild moist spring that may have boosted survival and development of soil-dwelling larval fireflies. Ah, but it appears that in addition to beneficial fireflies, there are other denizens of the soil which also enjoyed conditions favorable for their survival: plant-eating scarab beetles known as chafers.
Despoiling petals of my coneflowers is just another meal for the Oriental beetle.
Each year, I strive to raise a crop of interesting sunflowers to attract pollinators and birds to photograph and enjoy. However, over the past few weeks, leaves of my sunflowers disappeared in bits and pieces down the gullets of small scarab beetles known as Oriental beetles and Asiatic garden beetles. We met other members of this destructive branch of the scarab clan in previous episodes on Japanese beetles and green June beetles. Oriental beetles are yet another exotic invasive pest introduced to the US sometime before 1920. Originally detected in Connecticut, Oriental beetle now ranges from Maine to the Carolinas and west to the Heartlands. Like Oriental beetles, Asiatic garden beetles are invaders from Asia first detected on the east coast 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 these beetles 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 and Oriental beetles busily stripping away the foliage. Grubs of these little rascals, commonly known as white grubs, have been rooting about in my flower beds and lawn since their mothers deposited eggs in the soil early last summer. During the past year, conditions for survival of white grubs were spectacular. This heralded the possibility that the scarab clan would likely be problematic this year and unfortunately for our plants, the prediction seems to be coming true. By munching roots of grasses, annual, and perennial plants, white grubs can be important pests. Oriental beetle grub counts can approach as many as 60 per square foot of turf in heavy infestations. Here in Maryland by late spring larvae of chafers have completed development, pupated, and adults make their grand appearance in the first half of June. They will be present for the majority of the summer, devouring leaves and punishing blossoms in my landscape beds.
Leaves of my sunflowers have been disappearing over the past few weeks. Daytime inspections revealed nothing but a nocturnal recon nailed the perps, Oriental beetles like the patterned one on the left and brown Asiatic garden beetles like the one on the right. Watch as an Asiatic garden beetle devours a sunflower leaf. The handiwork of these rascals leaves me wondering if my poor sunflowers will bloom at all.
Managing Oriental beetles and other scarabs usually focuses on destruction of grubs in the turf and several products are available. One group of insecticides widely used for controlling white grubs including Japanese beetles and Oriental beetles are the neonicotinoids. These compounds have received much recent attention due to their impacts on pollinators, particularly bees. A fascinating study by Dan Potter and his colleagues at the University of Kentucky revealed that turf treated with the neonicotinoid insecticide clothianidin was not the best place for bumble bees to forage. White clover in plots treated with clothianidin expressed the insecticide in their blossoms, which in turn intoxicated the bees. However, once the clover blossoms had been removed by mowing, the exposure to bees was mitigated. A second white grub-killing insecticide evaluated in the study, chlorantraniliprole, presented no detectable adverse effect for the bumble bees.
Like other species of white grubs, Oriental beetle larvae consume the nutritious roots of plants.
In addition to synthetic insecticides, many folks recommend the use of nematodes to control white grubs in turf. Nematodes enter the grub and release a lethal bacterium. There are many different species and strains of nematodes. Dave Shetlar of the Ohio State University suggests that products containing strains of Steinernema carpocapsae are a bit less effective against beetle grubs than species in the clan named Heterorhabditis. You must wait until late July or August when grubs are in the soil, if you go the nematode route. 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. For me, plucking the beetles from the plants and either crushing their small bodies or giving them a swim in a cup of soapy water provides some retribution for their miscreant behaviors. There may be some good news on the horizon regarding these noisome grubs. Droughty conditions in June and July when female beetles deposit eggs in the soil generally disfavor survival of eggs and young larvae. While summer droughts may not benefit lawns and ornamental plants, they are a pariah to pesky chafers.
One more thing about Asiatic garden beetle. They are notorious for being attracted to light. I don’t know about you, but part of my regular nighttime routine involves reading a good book at bedtime. 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. 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 and have a look for these midnight marauders.
Acknowledgements
Excellent references such as “Assessing Insecticide Hazard to Bumble Bees Foraging on Flowering Weeds in Treated Lawns” by Jonathan L. Larson, Carl T. Redmond, and Daniel A. Potter, “Destructive Turfgrass Insects” by Daniel Potter, and the publication found at the following link were used in preparing this episode: https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0066375