Megacopta cribraria (F.) (Hemiptera: Heteroptera: Plataspidae) was first discovered in the United States in October 2009 on homes, structures, landscape plants, and kudzu (Pueraria montana Lour. [Merr.] variety lobata [Willd.] Maesen & S. Almeida) in northeastern Georgia (Eger et al. 2010, Suiter et al. 2010). Its identification was determined by morphological examination (Eger et al. 2010) and genetic analyses (Jenkins et al. 2010), thus, confirming the first occurrence of this species and the family Plataspidae in the New World. Its origin and mode of introduction remain unknown, although genetic sequencing is reportedly narrowing the possible country of origin (T.M. Jenkins, personal communication). Furthermore, mitochondrial DNA genome and gene sequences show that, to date, all specimens collected and analyzed from the expanded North American range originated from a single female ancestor, designated GA1 (GenBank HQ444175) (Jenkins and Eaton 2011).

Following its initial discovery, county Extension agents and professional pest control operators in northeast Georgia provided information on occurrence in neighboring counties. By 01 December 2009, the insect was confirmed in 9 Georgia counties – Barrow, Clarke, DeKalb, Gwinnett, Hall, Jackson, Oconee, Oglethorpe, and Walton (Suiter et al. 2010). Additional survey activities in 2010 confirmed the presence of the insect in 39 additional Georgia counties (Suiter et al. 2010) and 12 South Carolina counties (Greene 2010) by early August 2010.

Based upon a review of the available literature, Eger et al. (2010) listed 20 leguminous plants and 14 nonleguminous plants as hosts of Megacopta spp. throughout their Asiatic range. They noted that legumes appear to be the primary hosts of Megacopta spp., whereas most nonleguminous plants listed are likely incidental occurrences of Megacopta based on the existence of only one citation reporting the occurrence and the adult stage cited as being the only life stage observed. Zhang et al. (2012) subsequently assessed the suitability of 16 common leguminous plants for oviposition and development of M. cribraria in field choice tests in northeast Georgia. They observed adults on all but 2 of the species included in the study with the greatest abundance on yellowwood (Cladrastis kentukea [Dum. Cours.] Rudd), kudzu, and black locust (Robinia pseudoacacia L). Ovipositional preference was kudzu > soybean (Glycine max [L] Merrill) > Lespedeza spp., with 0 to few eggs observed on the remaining 8 species in the study. Furthermore, development from egg to adult occurred only on kudzu and soybean in their study.

The data presented herein represent updated confirmations of the occurrence of M. cribraria since the reports by Suiter et al. (2010) and Greene (2010). In addition, plants upon which M. cribraria were reported in the process of gathering these distributional data are included.

Materials and Methods

Initially, records of county confirmations of M. cribraria were maintained by D.R. Suiter (University of Georgia, Griffin Campus) for Georgia and by J.K. Greene (Clemson University, Blackville, SC) for South Carolina. That responsibility was shifted to W.A. Gardner (University of Georgia, Griffin Campus) in 2010. Additional confirmations of M. cribraria were then submitted to Gardner from universities, county Extension offices, regulatory agencies, professional pest control operators, and others. The date and location of confirmed occurrences were entered into a database along with host plant and stage(s) of the insect observed, when provided by the collector. State and county confirmations were maintained by Gardner on editable PowerPoint maps (Bruce Jones Design, Inc., Norwood, MA) and in the Early Detection and Distribution Mapping System (EDDSMapS) maintained by the University of Georgia Center for Invasive Species and Ecosystem Health. Both maps are available at http://www.kudzubug.org/distribution_map.cfm. New potential observations are received through personal communications and digital reports entered via an online reporting system (http://www.kudzubug.org/report/) or the Southeast Early Detection Network smart-phone app (SEEDN) (http://apps.bugwood.org/seedn.html). Observations submitted online are confirmed through.additional communication with the reporter, evaluation of the information and images submitted with a digital report, or visits to the location if sufficient information is not available. Upon confirmation of digital reports, observations are automatically added to the EDDSMapS, and the derived map is updated in real time.

Various sampling methods were used by surveyors depending upon location, host plant, surface, etc. Sweep netting was most frequently used in kudzu and soybean and was effective in yielding confirmations of all life stages. Visual inspections and observations were the second most used method of sampling for confirmation of occurrence.

Results and Discussion

Distribution. Megacopta cribraria was initially discovered in several northeastern Georgia counties in October 2009. Suiter et al. (2010) reviewed the initial discovery and distribution of the insect, whereas Eger et al. (2010) reported on its taxonomic identification and summarized available literature on its taxonomy, biology, pest status, and possible host plants. Both noted that neither this insect nor any other member of the family Plataspidae had been previously reported as occurring in the New World (Eger et al. 2010).

Reports of additional occurrences of the insect in areas near the Hoschton (Jackson Co.), GA, where the insect was first reported led to surveys of kudzu in surrounding counties. Those efforts confirmed the occurrence of the insect in 9 Georgia counties – Barrow, Clarke, Dekalb, Gwinnett, Hall, Jackson, Oconee, Oglethorpe, and Walton – by the end of 2009 (Fig. 1). The combined land area of these 9 counties, as provided in the 2010 U.S. Census (U.S. Census Bureau, U.S. Department of Commerce), initially infested with M. cribraria was 7,050 km². Megacopta cribraria was not recovered in several additional counties to the north, west, and south of these counties that were also surveyed during this time.

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By the end of 2010, M. cribraria was confirmed in 70 additional counties in Georgia, 16 counties in South Carolina, 2 counties in Alabama, and 1 county in North Carolina (Fig. 1). The insect had spread 200 linear km into central South Carolina, 175 linear km into southern Georgia, 130 linear km westward into Alabama, and 55 linear km northward into western North Carolina. The combined land area of the counties confirmed with M. cribraria by the end of 2010 was 98,816 km², a 14-fold increase in affected land area over the 7,050 km² reported at the end of 2009.

In 2011, the insect spread to 46 additional counties in Georgia, all remaining counties in South Carolina, 58 additional counties in North Carolina, 6 additional counties in Alabama, and 1 county in Virginia (Fig. 1). The combined land area of these additional counties in which M. cribraria was confirmed in 2011 was 188,577 km² bringing the total affected land area to 287,393 km², an almost 41-fold increase over the confirmed area at the end of 2009.

Approximately 75% of the land area added to the insect's distribution in 2011 occurred to the east and northeast of the areas confirmed in 2009 and 2010. The distance from the outer edge of the affected area in 2009 to the outer edges of affected areas in eastern and northeastern North Carolina at the end of 2011 ranged from 480 - 545 linear km. This significant expansion of the insect's range in a northeasterly and easterly direction in 2011 might be at least partially attributed to weather patterns that occurred in the region in the spring of 2011 when the existing La Niña climate pattern was the most intense on record (M. L'Heureux, Climate Prediction Center, Camp Springs, MD, cited by Rice and Welch [2011]). Jet stream air currents pushing predominantly from the west (Fig. 2), coupled with warm, moist air currents out of the south, created weather fronts and systems, some with long-lived supercells producing violent thunderstorms and tornadoes that moved across the region in a northeasterly and easterly direction. Weather fronts and air currents are known to transport insects for short and long distances (Johnson 1995) and were likely involved in the long-range dispersal of M. cribraria adults in spring 2011.

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In 2012, M. cribraria spread into Florida (16 counties confirmed), southeastern Tennessee (14 counties confirmed), Mississippi (4 counties confirmed), 33 additional counties in Georgia, 37 additional counties in Alabama, 30 additional counties in North Carolina, and 18 additional counties in Virginia confirmed (Fig. 1). The 392 counties in 8 states currently confirmed for M. cribraria have a land surface area of 497, 819 km², a 70-fold increase in affected land area since the end of 2009.

The first discovery M. cribraria in Mississippi was in kudzu in Warren Co. on the western side of the state in July 2012. The site was adjacent to an east-west interstate highway and was approximately 320 km from the western edge of the insect's range in Alabama at the time of the discovery. This confirmation underscores the hitchhiking ability of the insect. Prior to that discovery, the spread of this pest had been one of movement of the edge of the range as additional areas of infestations were confirmed. We might expect additional isolated pockets of the insect to be confirmed in other areas removed from the current expanded range as a result of hitchhiking on vehicles and in shipments of products.

The rapidity of the spread of this insect as reported in these surveys is a function of several factors including timing and intensity of survey activities as well as availability of preferred host plants for sampling (i.e., kudzu, soybean). Yet, the confirmed spread of this insect from 9 counties in 1 state into a total of 392 counties in 8 states in less than 3 years is phenomenal. The insect is indeed a strong flier. Large numbers of adults have been observed on exterior surfaces and on plants in rooftop gardens as high as 32 stories above ground level in high-rise buildings in Atlanta, attesting to their dispersal capabilities. Adults also are attracted to white and lightly-colored surfaces (Horn and Hanula 2011) including vehicles, airplanes and other equipment on which they could hitchhike. Furthermore, its preferred wild host is kudzu which is pervasive throughout and beyond its confirmed expanded range in the U.S. Additionally, the recent discovery of overwintering adults on cultivated soybean suggests that kudzu may not be necessary in the expanded range of M. cribraria.

Host plants. Thirty-three species of plants were reported as sources from which M. cribraria specimens were collected or upon which specimens were observed in this survey (Table 1). Of those 33 species, 17 are members of the family Fabaceae (legumes) with the remaining 16 species representing 14 families – Amaranthaceae, Asteraceae, Juglandaceae, Malvaceae, Moraceae, Musaceae, Myricaceae, Pinaceae, Poaceae, Rosaceae, Rutaceae, Salicaceae, Solanaceae, and Vitaceae. The preponderance of leguminous plants observed in this study also was reflected in the plants reported by Eger et al. (2010) in their review of the available literature on Megacopta spp. They listed 34 species, or groups (e.g., composites), as hosts with 20 of those in the family Fabaceae. Only 9 of the species reported in our survey were listed by Eger et al. (2010). Those were kudzu, soybean, lima bean (Phaseolus lunatus L.), Phaseolus vulgaris L., lablab bean (Lablab purpureus L. Sweet), pigeon pea (Cajanus cajan Druce) – all of which are legumes – and cotton (Gossypium hirsutum L.; family Malvaceae), wheat (Triticum aestivum L.; family Poaceae), and potato (Solanum tuberosum L.; family Solanaceae). An additional 6 species reported in our survey represent genera listed by Eger et al. (2010). Those are American wisteria (Wisteria frutescens L. [Poir.]), Chinese wisteria (W. sinensis [Sims] DC), Japanese wisteria (W. floribunda [Willd.] DC), Lespedeza sp., Satsuma mandarin (Citrus unshiu Marc), and tangerine (Citrus reticulata Blanco). Of the 6 species in this latter group, all but Satsuma mandarin and tangerine are legumes.

Table 1. List of plants on which M. cribraria was observed or collected in the southeastern U.S., 2009 - 2012.

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Table 1. Continued.

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Zhang et al. (2012) assessed 16 species of plants in various choice and no-choice tests of the potential host range of M. cribraria. Eight plants representing 7 species and 1 genus used in their study were recorded in our survey. Those were kudzu, soybean, lablab bean, American wisteria, Chinese wisteria, lespedeza, American yellowwood tree (Cladrastis kentuckea [Dum. Cours.] Budd), and black locust tree (Robinia pseudoacacia L.).

Sixteen plants on which M. cribraria was observed in our survey were not reported by Eger et al. (2010) or studied by Zhang et al. (2012). They are alligatorweed (Alternanthera philoxeroides [Mart.] Griseb.), cocklebur (Xanthium strumarium L.), alfalfa (Medicago sativa L.), peanut (Arachis hypogaea L.), the 2 species of clover (Trifolium spp.), sicklepod (Senna obtusifolia L.), pecan (Carya illinoinensis [Wagenh.] K. Koch), fig (Ficus carica [L.]), banana (Musa acuminata Colla), wax myrtle (Morella cerifera [L.]), loquat (Eriobotrya japonica Lindl.), wild blackberry (Rubus fruticosus L.), pine tree (Pinus spp.), muscadine (Vitus rotundiflora Michx.), and black willow (Salix nigra Marsh) (Table 1).

Caution must be exercised in recording a plant as a host of M. cribraria based merely on the presence of the insect on the plant. Indeed, Eger et al. (2010) noted that many of the nonleguminous plants listed in their review are probably records of incidental collections because the life stage observed was usually confined to adults, the observation of occurrence was rare or uncommon, or the record was reported in only one citation. Furthermore, Zhang et al. (2012) observed that, of the 16 plant species included in their study, M. cribaria completed development on only kudzu and soybean, egg masses were not deposited on several species, and significantly higher numbers of adults were observed on plant species that were not chosen as ovipositional substrates and did not support development from egg to adult.

Of the 33 plant species on which M. cribraria was observed in our survey, only adults were seen on or collected from 20 of those species (Table 1). Adults and egg masses were recorded from another 7 species; however, no nymphs were observed on those 7 species, even when observers attempted to follow development on the plants. Adults and nymphs were seen on 4 species – black locust (R. pseudoacacia), American wisteria (W. frutescens), Japanese wisteria (W. floribunda), and lima bean (P. lunatus). Eggs, nymphs, and adults were recorded on only 2 species – kudzu and soybean – which are currently the only confirmed reproductive hosts of M. cribraria in its expanded North American range.

Those 31 plant species on which complete development of M. cribraria was not confirmed are technically nonhosts for the insect. Yet, adults and, in some cases, nymphs were observed feeding upon some of these plants (e.g., wisteria, yellowwood, black locust, banana, fig, Citrus spp., Phaseolus spp.); damage, usually in the form of foliage loss, occurred on some species (e.g., wisteria, Phaseolus spp.) and was attributed to feeding damage by the adults. A significant number of the 21 plant species upon which only adults were observed are likely incidental nonhosts upon which adults simply rest or congregate. For example, adults were seen on cotton growing adjacent to heavily-infested soybean, and overwintering adults were routinely recovered from under the bark of pine trees.

Future prospects and concerns. Megacopta cribraria, as evidenced in this survey, rapidly spread into 8 southeastern U.S. states in less than 3 years after its introduction into the country. Its preferred wild host is kudzu, an invasive vine that is pervasive throughout the area currently occupied by the invasive insect in its expanding U.S. range. Until 2012, the spread of the insect was largely a progressive movement of the outer edges of the existing range as additional areas were confirmed as being infested. That year, isolated pockets of the insect were confirmed in other areas removed from the existing range, a likely result of hitchhiking on vehicles or other modes of transportation. Megacopta cribraria, with its propensity to disperse by hitchhiking, flying, and on prevailing wind currents and weather fronts, is expected to continue to spread beyond its current range in the U.S.

A number of trading partners with U.S. manufacturers and businesses have become concerned with the potential invasion of the pest on goods and products exported from infested areas of the U.S. Most recently, the discovery of 3 live and 3 dead adult M. cribraria in containerized shipments of blended cotton/polyester yarn by Honduran port inspectors at Puerto Cortesat initiated a remediation program for U.S. yarn exporters by the National Cotton Council of America (2012) to avoid trading sanctions.

Using correlative niche modeling, Zhu et al. (2012) predict that areas with high potential for invasion by M. cribraria include the southeastern U.S., southwestern Europe, southeastern South America, southern Africa, and eastern coastal Australia. Key predictive factors in their models included annual mean temperature, annual temperature range, temperature seasonality, precipitation seasonality, solar radiation levels, and topographic elevation. Whereas their analyses included the Normalized Difference Vegetation Index as an indicator of vegetative cover of the landscape, they did not account for the presence or absence of reproductive host plants, an important factor in the successful establishment of the insect.

Efforts are underway to manage the economic impacts of the pest in soybean production, reduce nuisance problems for the general public caused by adult insects in infested areas, and mitigate the potential exportation of the insect to international trading partners. To date, broad-spectrum insecticides have proven effective against the pest (Greene et al. 2012). The egg parasitoid Paratelenomus saccharalis (Dodd) (Hymenoptera: Platygastridae) also appears to be an excellent candidate for importation as a classical biological control agent because of its host specificity and wide geographic distribution in the Eastern Hemisphere (Ruberson et al. 2013).