Maladera formosae

{{Short description|Species of beetle}} {{Speciesbox | image = Maladera castanea.jpg | genus = Maladera | species = formosae | authority = ([[Ernst Brenske|Brenske]], 1898) | synonyms_ref = | synonyms = *''Autoserica formosae'' Brenske, 1899 *''Serica (Autoserica) korgei'' Petrovitz, 1967 *''Autoserica castanea'' Arrow, 1913 }}

'''''Maladera formosae''''', commonly known as the '''Asiatic garden beetle''' and formerly known as '''''Maladera castanea''''', is a species of beetle in the family [[Scarabaeidae]]. It is native to [[Japan]], [[China]], [[Taiwan]], [[South Korea]], [[North Korea]], and [[Russia]] but was introduced to [[North America]] in the 1920s where it is considered a [[Pest (organism)|pest]] of turfs, gardens, and crop fields. Adults are active in the summer during which they can be found feeding on leaves and flowers or gathering around light sources at night.<ref name=":0">{{Cite journal |last=Eckman |first=Laura E. |title=Host Plant Feeding Preferences of the Adult Asiatic Garden Beetle, Maladera castanea Arrow (Coleoptera:Scarabaeidae) |url=https://digitalcommons.lib.uconn.edu/gs_theses/714/ |journal=Master's Theses|date=29 January 2015 }}</ref>

== Morphology == Adults range in length from 8-9mm and are reddish-brown in color with an [[Iridescence|iridescent]] sheen.<ref name=":1">{{Cite web |last=Skelley |first=Paul E. |title=The Asiatic Garden Beetle, Maladera Castanea (Arrow 1913) (Coleoptera; Scarabaeidae), a White Grub Pest new to Florida |url=https://thefsca.org/wp-content/uploads/2022/03/ent425.pdf |website=Florida Department of Agriculture and Consumer Sciences}}</ref> Larvae, similarly to larvae of other species in the family [[Scarabaeidae]], are referred to as [[White grub|white grubs]]. ''M. formosae'' grubs grow from approximately 1.4 mm to 19 mm in length as they feed on plant roots and decaying plant material.<ref name=":2">{{Cite journal |last1=Held |first1=David W. |last2=Ray |first2=Charles H. |title=Asiatic Garden Beetle Maladera castanea (Coleoptera: Scarabaeidae) Grubs Found in Damaged Turf in Alabama |journal=Florida Entomologist|date=2009 |volume=92 |issue=4 |pages=670–672 |doi=10.1653/024.092.0426 |doi-access=free }}</ref>

''Maladera formosae'' are frequently mistaken for other species of scarab beetles. However, adults can be distinguished by their sturdy bodies, reddish-brown hue with an iridescent shine, concealed [[Labrum (arthropod mouthpart)|labrum]], [[Antenna (biology)|antenna]] with 10 segments, flat rear tibia featuring apical spurs separated by tarsal articulations, and elongated male genitalia with sizable, movable apical hooks.<ref name=":1" />

Larvae have C-shaped bodies, are predominantly white, and have brownish-orange white heads. ''M. formosae'' larvae can be distinguished from other white grub larvae by their prominent [[Maxilla|maxillary]] stipes, aggressive behavior, and unique [[Chevron (insignia)|chevron]]-shaped raster pattern underneath their Y-shaped anal slits.<ref name=":3" />

== Geographic distribution == ''Maladera formosae'' is native to [[East Asia]]. Aside from the [[Type locality (biology)|type locality]] Taiwan (formerly known as Formosa)<ref>{{cite journal|last=Brenske|first=E.|year=1898|title=Die ''Serica''-Arten der Erde|journal=Berliner Entomologische Zeitschrift|volume=43|pages=205-403|language=de|url=https://www.biodiversitylibrary.org/page/32553570}}</ref>, it was also native to China, Japan, North Korea, South Korea, and eastern Russia. It has also become established in the [[United States]] as an [[invasive species]].<ref name=":0" /> ''M. formosae'' was first discovered in North America in the United States, specifically in New Jersey in 1921.<ref name=":3">{{Cite thesis |last=Sturr |first=Connor |title=Quantifying Asiatic Garden Beetle (Maladera Formosae) Populations and Their Impacts on Commercial Mint Production |url=https://hammer.purdue.edu/articles/thesis/Quantifying_Asiatic_garden_beetle_i_Maladera_castanea_i_populations_and_their_impacts_on_commercial_mint_production/24749238 |website=Purdue University|date=2023 |doi=10.25394/PGS.24749238.v1 }}</ref> In its first decade in the United States, ''M. formosae'' spread throughout the East Coast. By 1933, ''M. formosae'' was recorded within 10 states and 1 district consisting of Connecticut, Delaware, Maryland, Massachusetts, New Jersey, New York, Pennsylvania, Rhode Island, South Carolina, Virginia, and Washington, D.C. It then spread southward and westward, leading to it being found by 2009 in at least 11 additional states, including Alabama, Georgia, Illinois, Indiana, Maine, Michigan, New Hampshire, North Carolina, Ohio, Vermont, and West Virginia with possible identification in Kansas and Missouri. The most recent state in which ''M. formosae'' was newly reported is Florida in 2012. ''M. formosae'' has also been identified in the two [[Canada|Canadian]] provinces of Quebec in 1996 and Nova Scotia in 2003.<ref name=":0" /> In total, ''M. formosae'' is now found in the United States in at least 24 states and Canada in 2 provinces.<ref name=":4">{{Cite journal |last1=Pekarcik |first1=Adrian J. |last2=Clem |first2=Scott C. |last3=Akred |first3=Kyle J. |last4=Tilmon |first4=Kelley J. |title=Quick Sex-Determination of the Asiatic Garden Beetle, Maladera castanea (Coleoptera: Scarabaeidae) |url=https://scholar.valpo.edu/tgle/vol55/iss1/8/ |journal=The Great Lakes Entomologist|date=2022 |volume=55 |doi=10.22543/0090-0222.2417 }}</ref>

== Diet == Adult beetles feed most actively during the [[Nocturnality|night]]. Their diet consists predominantly of the [[foliage]] and flowers of various plants totaling over 100 different species. They also feed sparingly on blades of grass. Foliage consumption typically progresses inwards and, when beetles are abundant, only the [[midvein]] of the leaf will remains. This damage is often not attributed to ''M. formosae—''their nighttime feeding means they are rarely observed in the act. [[File:Ocimum basilicum CG NBG LR.jpg|thumb|240x240px|[[Basil]] (preferred [[Host (biology)|host plant]] for ''Maladera formosae'')]] Adults prefer eating flowers like [[Aster (genus)|asters]], [[chrysanthemum]]s, [[dahlia]]s, [[goldenrod]]s, [[rose]]s, [[strawflower]]s, [[Helianthus|sunflowers]], and [[zinnia]]s.<ref name=":2" /> Grubs act as pests for various [[Ornamental plant|ornamentals]], turfs, and gardens along with field crops, such as [[sweet potato]]es, [[soybean]]s, and [[maize|corn]].<ref name=":1" /> They typically feed on plant roots and decaying plant material.<ref name=":0" /> Field and laboratory experiments have been performed assessing adult beetle preference for different [[Host plant|host plants]]. Field experiments found that [[basil]] was preferred compared to [[beetroot|beet]], [[carrot]], [[eggplant]], [[hot pepper]], [[kohlrabi]], [[parsnip]], [[sweet pepper]], and [[turnip]]. Laboratory experiments found that basil was preferred when compared to [[American sweetgum]], [[Viburnum dentatum|arrowwood viburnum]], [[elderberry]], [[green ash]], [[red maple]], and [[sugar maple]], but equally preferred when compared to beets and kohlrabi.<ref name=":0" />

== Life cycle == ''Maladera formosae'' undergoes a similar life cycle to other white grub pests like [[Japanese beetle|Japanese beetles]] and [[Cyclocephala|masked chafers]].<ref name=":3" /> It undergoes a [[complete metamorphosis]] with one generation each year, though the exact timing of its life stages depends on temperature and humidity. Research has, however, suggested that multiple generations can be produced each year, granted a sufficiently warm and moist environment is provided.<ref name=":0" />

=== Eggs === After mating in July or August, females lay groups of eggs 1-10cm below the surface.<ref name=":0" /> They typically lay 3-15 groups of up to 20 eggs each with total egg counts averaging approximately 60 eggs, though as many as 178 eggs have been observed for a single female beetle.<ref name=":3" /> Females prefer [[Ovipositor|ovipositing]] in moist, sandy soils that are near host plants or beneath shady plants.<ref name=":0" /> These preferred environments are usually well-irrigated, weedy patches of turf. Eggs absorb and swell from moisture in soil over time, which is consistent with other white grub species.<ref name=":2" /> Eggs hatch within 10 days with most larvae emerging in mid July.<ref name=":3" />

=== Larvae === [[Larva|Larvae]] undergo three [[instar]]s, growing from 1.4mm to 19mm.<ref name=":2" /> First-instar larvae feed on young roots and decaying plant material in shallower soil up to 13cm deep.<ref name=":0" /> Larvae [[Moulting|molt]] to enter their second and third instars once they have eaten enough. They typically enter their third instar by September or mid October. Larvae then [[Overwintering|overwinter]] by burrowing and becoming dormant beneath the [[frost line]], 15-30cm below the surface.<ref name=":3" /> Approximately one-quarter of larvae are slow to mature or late to hatch. Such larvae often do not reach their third instar before the arrival of winter. Some of these larvae can survive the winter in their second instars, but first-instar larvae typically fail to do so. In the following spring, surviving larvae will burrow closer to the surface and continue feeding 13cm deep or less in the soil.<ref name=":0" />

=== Pupae === After approximately 10 months, third-instar larvae [[Pupa|pupate]] in June or July by compacting soil 4-10cm underneath the surface. They enter their [[Prepupa|prepupal]] stage first, becoming inactive for 4 days before fully pupating. After 10 days, they emerge as adults in July but remain in their pupal skin for several more days as their [[Exoskeleton|exoskeletons]] harden.<ref name=":0" />

=== Adults === Adults usually live no more than a month but can live for up to 100 days. They are usually seen from the period ranging from late June to the end of October during which they feed, mate, and reproduce.<ref name=":3" />

== Parental care == [[File:Corn and Soybeans Growing in a Field, Morgan Road, Pittsfield Township, Michigan.JPG|thumb|242x242px|Soybean and corn fields]] Females prefer specific host plants, soil moistures, and types of soil for [[Ovipositor|ovipositioning]]. Specifically, moist, cool soil that is shaded by canopies is preferred.<ref name=":6">{{Cite journal |last=Hallock |first=Harold C. |date=1936-04-01 |title=Notes on Biology and Control of the Asiatic Garden Beetle |url=http://dx.doi.org/10.1093/jee/29.2.348 |journal=Journal of Economic Entomology |volume=29 |issue=2 |pages=348–356 |doi=10.1093/jee/29.2.348 |issn=1938-291X|url-access=subscription }}</ref><ref name=":7">{{Cite journal |last1=Held |first1=David W. |last2=Ray |first2=Charles H. |date=December 2009 |title=Asiatic Garden BeetleMaladera castanea(Coleoptera: Scarabaeidae) Grubs Found in Damaged Turf in Alabama |journal=Florida Entomologist |volume=92 |issue=4 |pages=670–672 |doi=10.1653/024.092.0426 |issn=0015-4040 |doi-access=free}}</ref> ''M. formosae'' is mainly found in regions with long grass, but it shows no preference for ovipositioning in short or long grass environments. However, females have demonstrated a preference for corn-soybean fields for oviposition.<ref>{{Cite journal |last1=Buckley |first1=P. A. |last2=McCarthy |first2=Molly G. |date=May 1994 |title=Insects, Vegetation, and the Control of Laughing Gulls (Larus atricilla) at Kennedy International Airport, New York City |url=http://dx.doi.org/10.2307/2404544 |journal=The Journal of Applied Ecology |volume=31 |issue=2 |pages=291 |doi=10.2307/2404544 |jstor=2404544 |bibcode=1994JApEc..31..291B |issn=0021-8901|url-access=subscription }}</ref> Moist environments can prevent the female's eggs from drying out.<ref name=":6" /> As a mechanism for pest control, modifying these variables can reduce oviposition to regulate the number of this species. Furthermore, studying the pheromones that this species possesses can be useful for controlling mating and oviposition rates to monitor species numbers.<ref name=":6" /><ref name=":7" />

== Sex determination == In theory, the [[Sexual dimorphism|sex]] of individual beetles can be identified by females having more pronounced front tibia. However, this is difficult to identify in individual beetles given that they vary in size and no database for leg size measurements exists. Instead, [[Sex-determination system|sex determination]] for ''M. formosae'' can be quickly performed under a [[dissecting microscope]] or [[hand lens]] by assessing posterior abdominal sternite and pygidium orientation. The pygidiums of males pinch the edges of their sternites, while the pygidiums of females do not do so.<ref name=":4" />

== Ecosystem interactions == ''Maladera formosae'' is typically considered a minor pest of turf and [[Ornamental plant|ornamentals]]. However, these beetles quickly become a major nuisance when they grow to be locally abundant: larval radicular feeding and adult foliar feeding cause major damage.<ref name=":5">{{Cite journal |last1=Koppenhofer |first1=Albrecht M. |last2=Fuzy |first2=Eugene M. |title=Biological and chemical control of the Asiatic garden beetle, Maladera castanea (Coleoptera: Scarabaeidae) |journal=Journal of Economic Entomology|date=2003 |volume=96 |issue=4 |pages=1076–1082 |doi=10.1603/0022-0493-96.4.1076 |doi-broken-date=18 January 2026 |pmid=14503577 }}</ref>

=== Midwestern crop fields === ''Maladera formosae'' has become a problem for crop fields found throughout Ohio, Michigan, and Indiana, for which it has been reported as being even more damaging than other white grub species. Many crop fields in these states undergo a [[crop rotation]] between [[Mentha|mint]], [[corn]], and [[Soybean|soybeans]]. It is believed by researchers that ''M. formosae'' populations persist throughout the entirety of these crop rotations, feeding on the crops themselves and causing significant damage. Researchers have estimated that ''M. formosae'' larvae cause a loss of $325 per acre of land for growers in these states.<ref name=":3" />

=== Strawberry fields === [[File:Maladera formosae on Murraya paniculata leaf.jpg|thumb|''Maladera formosae'' on what appears to be a [[jasmine]] plant]] Various root diseases and root-feeding insects have been found to harm [[perennial]] [[strawberry]] cultivation within the northeastern United States. The most important of these damaging factors are black [[root rot]] disease caused by ''[[Rhizoctonia fragariae]]'' and physical root damage caused by white grubs and [[Weevil|root weevils]]. Alongside ''[[Anomala orientalis]]'', ''M. formosae'' has been identified as being amongst the most common white grub pests of Connecticut strawberry fields. Research studies have shown that physical damage by ''M. formosae'' did not affect rates of root infection.<ref>{{Cite journal |last1=LaMondia |first1=James A. |last2=Cowles |first2=Richard S. |title=Comparison of Pratylenchus penetrans Infection and Maladera castanea Feeding on Strawberry Root Rot |journal=Journal of Nematology|date=2005 |volume=37 |issue=2 |pages=131–135 |pmid=19262852 |pmc=2620957 }}</ref>

=== Insecticide control === Current pest control options for ''M. formosae'' are limited, relying primarily on [[Insecticide|insecticides]] that are either ineffective or unevaluated for ''M. formosae''. The [[Food Quality Protection Act|Food Quality Protection Act of 1996]] has also enacted restrictions that ban many [[carbamate]] and [[organophosphate]] insecticides traditionally used for white grub control. Of such options, only [[carbaryl]], a carbamate, and [[trichlorfon]], an organophosphate, remain viable for use on [[turfgrass]].<ref name=":5" />

[[Imidacloprid]], a [[neonicotinoid]], and halofenozide, a molt-accelerating compound, have been proven to be effective in controlling white grub populations. They are, however, limited in only being able to target eggs and larvae, which are difficult to detect due to being subterranean. Researchers believe this conflict in effectiveness of insecticides leads to overtreatment and mistreatment of agricultural fields with minimal or nonexistent ''M. formosae'' presence. This has the potential to create negative implications, such as expensive financial losses, increased resistance development, and unintended environmental consequences.<ref name=":5" />

Though grubs typically cause the most damage by feeding on plant roots, ''M. formosae'' adults are still an agricultural concern as they can defoliate several rows of field crops every night and their dispersal determines the location of future larval populations.<ref name=":0" /> Grub populations are difficult to notice but respond to limited insecticides. Adult populations are easier to notice than grub populations but respond to even fewer [[pesticide]] options, presenting a separate though related problem when compared to that of grubs.

=== Nematode control === [[Entomopathogenic nematode|Entomopathogenic nematodes]] have been identified by researchers as an effective [[Biological pest control|biological control]] for other white grub species. However, their efficacy for ''M. formosae'' is still being studied as the beetle has been shown to be less susceptible to common nematode strains, such as ''[[Heterorhabditis bacteriophora|Heterohabditis bacteriophora]]'' and ''[[Steinernema|Steinernema glaseri]]'', when compared to other white grub species. Another isolated strain, ''[[Steinernema|Steinernema scarabaei]]'', has been identified in research studies as a possible alternative to pesticides for ''M. formosae'' given its high [[pathogenicity]] for ''M. formosae''.<ref name=":5" />

=== Sampling methods === Due to grubs being subterranean and adults being nocturnal, ''M. formosae'' infestation can be difficult to recognize. Researchers have compared the effectiveness of various sampling techniques, such as using compact cutters, golf hole cup cutters, and wire-mesh bait stations to improve methods for quantification of ''M. formosae'' grub population density. They found that the golf hole cup cutters presented the best option, as it is more sensitive than the other methods.<ref>{{Cite journal |last1=Pekarcik |first1=Adrian J. |last2=Raudenbush |first2=Amy L. |last3=Richer |first3=Eric |last4=Tilmon |first4=Kelley J. |title=Active and passive sampling methods for grubs of the Asiatic garden beetle, Maladera formosae (Coleoptera: Scarabaeidae), in a corn-soybean rotation |journal=Crop Protection|date=2023 |volume=165 |article-number=106165 |doi=10.1016/j.cropro.2022.106165 |doi-access=free |bibcode=2023CrPro.16506165P }}</ref>

==References== {{Reflist}}

[[Category:Maladera|formosae]] [[Category:Beetles of China]] [[Category:Beetles of Japan]] [[Category:Invasive agricultural pests]] [[Category:Taxa named by Ernst Brenske]]