A homeowner brought these beetles to The Ohio State University’s Plant Pest Diagnostic Clinic, (PPDC) in mid-June 2024. The beetles look like European chafers but have iridescent elytra and are smaller in size. They were observed damaging the homeowner’s vegetables including basil, especially at night, and although they searched, the homeowner could not find these beetles during the day.
1. AGB eating foliage at night, 2. At dusk, they burrow into the soil and hide during the day, 3. AGB can completely destroy crops. Images © Barbara Crawford, Marshallville, OH
Taxonomy and identification
This beetle is commonly known as asiatic garden beetle (AGB), Maladera formosae (Brenske 1898), (formally known as Maladera castanea (Arrow, 1913)) and is native to Japan, China, South and North Korea, and Russia. AGB was likely introduced to North America in the 1910s or 1920s. It was first discovered in New Jersey in 1921. Since then, AGB has spread throughout the Northeastern region of the United States, and in 2012, AGB was reported in Alabama and Florida. As of 2024, AGB is reported in at least 24 US states, as well as Quebec and Nova Scotia in Canada.
AGB belongs to the family Scarabaeidae in the Order Coleoptera. The size of the adult is about 10 mm on average. These beetles are similar in appearance to chafer beetles, especially European chafers, oriental beetles (there are 3 color variations), rose chafers, and June beetles.
AGB can be identified in the field due to their smaller size, iridescent elytra, elytra not completely covering the apical portion of the abdomen (pygidium), and strongly flattened hind femurs.
Economically important beetles in the family Scarabaeidae found in Ohio in comparison to AGB 1. Two morphological variations of green June beetle, Cotinus nitida, 2. Two morphological variations of May/June beetle, Phyllophaga fusca, 3. Southern masked chafer, Cyclocephala lurida, 4. European chafer, Rhizotrogus majalis, 5. . Northern masked chafer, Cyclocephala borealis, 6. Japanese beetle, Popillia japonica, 7. Asiatic garden beetle, Maladera formosae, 8. Three morphological variations of Oriental beetle, Exomala orientalis, 9. Black turfgrass ataenius, Ataenius spretulus, and morphologically similar Aphodius spretulus.
In addition, adults can be separated from other similar-looking beetles by the hidden labrum, antennae with 10 segments, wider and strongly flattened hind tibia, and bi-clawed tarsal claws.
A distinctive feature of AGB larvae is their pear-shaped white cheeks on each side of the head. This feature is unique and serves as a key characteristic to differentiate AGB larvae from other similar white grubs.
Characters to identify M. formosae. 1-Iridescent elytra, 2. Labrum is indistinct from top. 3. Bi-clawed tarsal claws. 4. 10 segmented antennae. 5. Strongly flattened hind tibia and barrel-shaped body. 6. Mature larvae with white cheeks.
Life cycle in Northern Ohio
AGB adults are nocturnal, and they feed on the foliage of a wide variety of crops, ornamental plants and weeds, consuming entire plants including the veins and petioles. The adults are active from mid-June to late September in Northern Ohio.
Females of AGB lay eggs in small batches in the soil during the summer. These eggs typically hatch within 1-2 weeks after being laid. Upon hatching, the young first instar larvae begin feeding on roots and organic matter in the soil. As the soil temperature starts to drop in late September and early October, the larvae burrow deeper into the soil. This behavior helps them survive the cold winter months. They overwinter as 2nd or 3rd instars, which are less vulnerable to the cold compared to younger larvae. Sometimes, females will lay eggs late in the growing season. We have observed inactive 1st and 2nd instar larvae during May and June when sampling soils planted with corn and soybean. This finding suggests that these larvae hatched late during the previous growing season.
As the soil warms up in the spring, the larvae of AGB start moving upwards in search of roots to feed on, including those of various weed species. The last instar larvae pupate in late May and June. The pupal stage typically lasts 1-2 weeks, depending on soil temperature. After pupation, adults emerge in June and July. Following emergence, adult AGB begin feeding on the foliage of many plants. Adult AGB are strong fliers and can travel considerable distances. They are attracted to lights and can often be found near porches and street lights. After mating, females burrow into the soil during the daytime to lay eggs.
During field visits to survey these beetle grubs in Northern Ohio, before planting corn and soybean, we observed the grubs aggregating around the root systems of weeds especially Conyza canadensis, commonly known as marestail/horseweed/Canada fleabane. This behavior can assist farmers and agronomists in making informed decisions regarding pest management strategies, including the timing of treatments or cultivation practices.
Ecology and management of AGB in home garden setting
Adults continue to feed at night and hide during the day during the summer, damaging many crops on their way.
The most effective way to control adult beetles in a backyard setting is to hang a light bulb at a height of 1 foot and keep a pan of soapy water underneath. This technique is most effective if implemented as soon as you see the damage. Visiting the crops at night is important, to see if the beetles are present and active since there are many beetle species that produce crop damage similar to AGBs but are active during the day.
Feeding AGB adults to chickens as a method of control can indeed be an effective and natural approach, especially for homeowners with backyard chickens. Chickens are known to eat insects as part of their diet, and they find AGB adults particularly palatable. Allowing chickens access to areas where AGB adults are present can help reduce the beetle population.
Insecticides with Bacillus thuringiensis galleria (Btg) bio-insecticide as the active ingredient can be used to control AGBs. This insecticide will control any adults on vegetation and larvae in the soil upon contact. These products are mostly effective for Japanese beetles, asiatic garden beetles, June beetles, oriental beetles as well as European chafers, and Southern and Northern masked chafers. Check the label of the product, it has to specifically say the name Btg on it. Read the label carefully before application.
The advantages of Btg products are that they will not harm insect pollinators or other beneficial natural enemies (such as parasitic wasps and beneficial nematodes, which also kill white grubs). Also, these products claim to be effective at any temperature range and stable for long periods of time, unlike ‘milky spores’ (Milky spores is a disease caused by a soil-dwelling, bacterium (Paenibacillus popilliae) in white grubs).
References
Asiatic Garden Beetle identification and management tips - https://www.youtube.com/watch?v=AbfP4Airu5A
Identification, monitoring, & management of Asiatic garden beetle in field crops https://aginsects.osu.edu/sites/aginsects/files/imce/AGB%20in%20field%20crops%202019.pdf
Pekarcik, Adrian J.; Clem, C. Scott; Akred, Kyle J.; and Tilmon, Kelley J. 2022. "Quick Sex-Determination of the Asiatic Garden Beetle, Maladera castanea (Coleoptera: Scarabaeidae)," The Great Lakes Entomologist,vol 55 (1)DOI: https://doi.org/10.22543/0090-0222.2417
Pekarcik, A. J. (2022). Ecology and Management of the Asiatic Garden Beetle, Maladera formosae, in Corn-Soybean Rotated Agroecosystems (Order No. 29705016). Available from Dissertations & Theses @ Big Ten Academic Alliance; Dissertations & Theses @ Ohio State University; ProQuest Dissertations & Theses A&I; ProQuest Dissertations & Theses Global. (2720408058). https://proxy.lib.ohio-state.edu/login?url=https://www.proquest.com/dissertations-theses/ecology-management-asiatic-garden-beetle-em/docview/2720408058/se-2
Pekarcik , Adrian J., Amy L. Raudenbush, Eric Richer, Kelley J. Tilmon. 2023. Active and passive sampling methods for grubs of the Asiatic garden beetle, Maladera formosae (Coleoptera: Scarabaeidae), in a corn-soybean rotation, Crop Protection, Volume 165, 106165, ISSN 0261-2194, https://doi.org/10.1016/j.cropro.2022.106165
Sturr, Connor Eric; richmond, Doug; Y. Long, Elizabeth; Krupke, Christian (2023). Quantifying Asiatic garden beetle (Maladera formosae) populations and their impacts on commercial mint production. Purdue University Graduate School. Thesis. https://doi.org/10.25394/PGS.24749238.v1
