Seasonal Dynamics and Plant Preferences of Megacopta
cribraria, an Exotic Invasive Insect Species in the Southeast
Sarah M. Huskisson, Kayla L. Fogg, Taylor L. Upole, and Caralyn B. Zehnder
Southeastern Naturalist, Volume 14, Issue 1 (2015): 57–65
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S.M. Huskisson, K.L. Fogg, T.L. Upole, and C.B. Zehnder
22001155 SOUTHEASTERN NATURALIST Vo1l4.( 114):,5 N7–o6. 51
Seasonal Dynamics and Plant Preferences of Megacopta
cribraria, an Exotic Invasive Insect Species in the Southeast
Sarah M. Huskisson1, Kayla L. Fogg1, Taylor L. Upole1, and Caralyn B. Zehnder1,*
Abstract: - Megacopta cribraria (Kudzu Bug) (Hemiptera: Plataspidae) is an invasive
insect in the Southeast. In Baldwin County, GA, we found adult Kudzu Bugs at high
abundances throughout the summer, while juveniles showed peaks in early July and September.
We conducted a series of choice-preference tests and determined that the insects
preferred Glycine max (Soybean) over Phaseolus lunatus (Lima Bean). Additionally,
they preferred Pueraria montana var. lobata (Kudzu) over Soybeans, highlighting the
role of Kudzu as a primary host plant. Additionally, Kudzu Bugs continued to feed on
Soybeans, even in the presence of Kudzu.
Introduction
Megacopta cribraria (F.) (Hemiptera: Plataspidae) (Kudzu Bug) is an invasive
insect species in Georgia and throughout the southeastern US. The Kudzu Bug was
first documented in 2009 in 9 northeast Georgia counties (Suiter et al. 2010). In
the fall of 2010, Kudzu Bugs were confirmed in more than 60 Georgia counties in
addition to North Carolina and South Carolina (Suiter et al. 2010), and they have
subsequently spread into 8 southeastern states, including South Carolina, Georgia,
North Carolina, Alabama, Virginia, Tennessee, Florida, and Mississippi (Gardner et
al. 2013). The most frequent host plant of the Kudzu Bug is Pueraria montana var.
lobata (Willd.) Maesen & S. Almeida (Kudzu), though it commonly feeds on other
legume species, including economically important crops like Glycine max (L.)
Merrill (Soybean). The Kudzu Bug is native to Asia, and, even though it is widely
distributed there, it is not usually a major pest of legumes in its native home range
(Ruberson et al. 2013). In the southeastern US, it thrives on the abundant Kudzu,
which was introduced into the US from Japan in 1876 and has since spread across
the region (Forseth and Innis 2004).
The Kudzu Bug is the only member of its family (Plataspidae) in the Western
Hemisphere (Ruberson et al. 2013). Megacopta cribraria is known by many
common names, including Kudzu Bug, Bean Plataspid, Globular Stinkbug, and
Lablab Bug, because it feeds on the legume Lalab purpureus (L.) Sweet (Lablab)
in its native range. The insect is grayish-brown in color and has a square “shield”
on its back; adults are 4–6 mm long (Eger et al. 2010). Kudzu Bugs release an
offensive odor when disturbed, and they produce a substance when crushed that
can stain cloth and wood. Additionally, the nymphs can cause minor skin irritation
(Ruberson et al. 2013). Kudzu Bugs are attracted to light-colored surfaces,
1Department of Biological and Environmental Sciences, CBX 081, Georgia College and State
University, Milledgeville, GA 30161. *Corresponding author - caralyn.zehnder@gcsu.edu.
Manuscript Editor: Robert Jetton
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including houses, where they often congregate in high densities, attracting the
attention of homeowners and contributing to their classification as an urban pest
species (Ruberson et al. 2013).
The life history of the Kudzu Bug has been very well described by Eger et al.
(2010). Kudzu Bugs overwinter as adults clustered in sheltered areas (e.g., under
loosened tree bark) in the vicinity of fall host plants, which often include Kudzu.
Adults become active again in the spring and search for suitable host plants. Adult
females lay an average of 16 eggs per cluster on leaf nodes or on the undersides of
leaves (Zhang et al. 2012). There are 2 generations per summer in the Southeast.
Eggs are covered with symbiotic bacteria from the mother, which the offspring
consume after they hatch. Juvenile insects stay together on the host plant, normally
around the leaf buds (Eger et al. 2010).
Gardner et al. (2013) collected Kudzu Bugs from 33 plant species representing
15 families. Approximately half of the host plants were members of the Fabaceae
(legume family), and Kudzu was the most frequently reported host. Currently,
Kudzu and Soybean are the only confirmed reproductive host plants of the Kudzu
Bug in the North American range (Zhang et al. 2012).
Our research examined seasonal dynamics of the Kudzu Bug and its resting
and feeding-plant preference. We hypothesized that insect abundance at the
Oconee River Greenway in Baldwin County, GA, would increase throughout
the growing season and then decrease in the fall. Baldwin County is located in
central Georgia along the Fall Line that separates the Piedmont and the Coastal
Plain physiographic provinces. Because Kudzu Bugs have the potential to impact
commercially important crops, we examined preference among 3 legume species:
Soybean, Phaseolus lunatus L. (Lima Bean), and Kudzu. Soybeans are an
economically important crop grown for oil production, animal protein, and human
consumption. Recent research has shown that Kudzu Bug herbivory can decrease
Soybean yields (Seiter et al. 2012). Lima Beans are also cultivated for human
and animal consumption, and they are often used as a cover crop. Kudzu is found
ubiquitously along roadsides and other habitats throughout the Southeast where it
is one of the region’s most serious invasive plant species (Blaustein 2001). Additionally,
we investigated if Soybean inoculation with Rhizobium spp. (rhizobium)
influenced host-plant choice. We examined preference between the following
pairs: Soybeans and Lima Beans, Soybeans and Kudzu, and rhizobium-inoculated
and non-inoculated Soybeans.
Materials and Methods
Seasonal dynamics
The Oconee River Greenway is a community park adjacent to the Oconee River
in Milledgeville, GA (33.08°N, 83.21°W). We chose 10 sites at the Greenway
within an area of 0.51 km2 based on Kudzu abundance. Sites were 3 m2, were separated
by wooded areas, and contained only Kudzu. We sampled sites once a week
at 16:00 hr from 3 May until 20 November 2012, except for a 2-week interval in
mid-summer. We used sweep nets to collect the samples by sweeping the nets
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2015 Vol. 14, No. 1
through the Kudzu vines 15 times at each site. We placed the collected insects
in Ziplock® bags with cotton balls soaked in ethyl acetate and kept them in the
freezer until they could be counted and sorted based on age-class (adults versus
juveniles). We determined insect-age class by size and the presence or absence of
fully developed wings.
Plant-preference tests
We grew Soybeans and Lima Beans in the Georgia College campus greenhouse.
Seeds were planted individually in 10 cm x 10 cm plastic pots. We watered the
plants as needed, they received natural light, and were regularly rotated to reduce
the effects of environmental variation within the greenhouse. The seedlings were
~5 weeks old at the start of the experiments. For the Kudzu used in the preference
tests, we placed branches collected from the Oconee River Greenway in water and
used within 24 h.
We conducted 3 sets of preference tests in the greenhouse: Soybeans vs. Lima
Beans, Soybeans vs. Kudzu, and rhizobium-inoculated vs. non-inoculated Soybeans.
For each test, we set up mesh cages (BugDorm 2120, MegaView Science
Company, Taichung, Taiwan) that measured 60 cm x 60 cm x 60 cm and contained
the plant pairs described below. We purchased the Butterbean Soybean variety
from Johnny’s Selected Seeds (Albion, ME) and Burpee’s Lima Fordhook 242
Bush seeds from Lowe’s (Lowe’s, Mooresville, NC). We made visual estimates to
qualitatively ensure that biomass was equal for each species in each cage.
We conducted the Soybean vs. Lima bean tests in September 2012. We placed
15 cages in the greenhouse, each with one 5-week-old non-inoculated Soybean
seedling and one 5-week-old Lima Bean seedling. We placed 15 adult Kudzu Bugs
collected from a variety of plants including Kudzu from the Oconee River Greenway
in each cage within 4 h of collection. We then monitored the insects once a
day between 13:00 and 15:00 h for the following 9 days and recorded the number
of insects per plant for each cage starting 24 h after the initial setup. On average, 3
insects per cage died over the course of the choice-preference test.
We conducted preference tests between Soybeans and Kudzu in September
2013. We grew 40 non-inoculated Soybean seedlings in individual pots in the
greenhouse. We prepared 20 cages, each containing one Soybean plant, a visually
equivalent amount of Kudzu, and 10 Kudzu Bugs. We monitored each cage twice
daily for 48 h after initial setup—once at ~08:00 h and again at ~16:00 h.
We conducted preference tests between inoculated and non-inoculated Soybeans
in October 2013. We grew 40 Soybean seedlings in individual pots in the
greenhouse. We randomly selected 20 of the Soybean seedlings and inoculated
them with Bradyrhizobium japonicum, a nitrogen-fixing bacterium (N-DURE A
Premium Inoculant for Soybeans, Lot # K165, INTX Microbials, LLC, Kentland,
IN) using the slurry method. The other 20 seedlings were non-inoculated. We set
up 20 cages, each containing one non-inoculated Soybean plant, an equivalently-
sized inoculated Soybean plant, and 10 Kudzu Bugs; preference tests were
conducted as described above for the Kudzu–Soybean preference tests.
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We treated each cage as a replicate in the preference tests. We analyzed Kudzu
Bug preference using a two-tailed t-test in Microsoft Excel, with plant type as the
independent variable and the number of insects as the dependent variable. These
analyses only included insects present on plants and did not include insects that
were elsewhere in the cage because we were only concerned with insects that were
feeding or resting on the plants.
Results
Seasonal dynamics
Our Kudzu Bug sampling at the Oconee River Greenway lasted 7 months, and
included 24 sampling occurrences; in total, we collected 8860 insects. Kudzu Bug
peak relative abundance occurred in early July through late August (Fig. 1). We
found adults at high abundances throughout the summer, while juveniles showed
a peak in early July and then another small peak in September. The relative abundance
of insects in both life stages sharply declined in November.
Plant preference
In the preference tests between Soybeans and Lima Beans, Kudzu Bugs showed
a significant preference for Soybeans over Lima Beans (Table 1). On all 9 days of
the experiment, Kudzu Bug density was significantly higher on the Soybean seedlings
than on the Lima Bean seedlings. In the preference tests between Kudzu and
Soybeans, Kudzu was significantly preferred over Soybeans during the afternoon
sampling of the first day (Day 1 AM t38 = 1.38, P = 0.180; Day 1 PM t38 = 2.34, P =
0.025; Day 2 AM t38 = 1.38, P = 0.175; Day 2 PM t38 = 1.44, P = 0.159; Fig. 2).
Kudzu Bugs did not show any preference between inoculated and non-inoculated
Soybeans (Day 1 AM t38 = 0.254, P = 0.801; Day1 PM t38 = 0.677, P = 0.502; Day
2 AM t38 = 0.085, P = 0.933; Day 2 PM t38 = 1.529, P = 0.135; Fig. 3).
Discussion
We investiagted seasonal abundance patterns and plant preferences of Kudzu
Bugs. The insects preferred Soybeans over Lima Beans. When Kudzu and Soybeans
were compared as food sources, Kudzu Bugs prefered Kudzu during one of
Table 1. Mean Kudzu Bug density (SD) on Soybean or Lima Bean (n = 15) on each day of the feedingpreference
test. Mean insect density on Soybean versus Lima Bean for each day was compared using
a 2-tailed t-test (df = 28 for all t-tests). These analyses only included insects on plants and did not
include insects that were on the cage itself.
Day 1 Day 2 Day 3 Day 4 Day 5 Day 6 Day 7 Day 8 Day 9
Soybean 6.20 6.93 4.93 6.53 5.80 4.07 5.67 5.13 3.53
(2.3) (2.1) (1.7) (2.8) (2.5) (3.0) (3.3) (3.4) (2.7)
Lima Bean 2.33 2.87 1.67 1.87 1.60 1.07 0.80 1.00 0.93
(2.9) (2.5) (1.6) (2.0) (2.2) (1.6) (1.1) (1.5) (1.6)
t-stat 3.965 4.833 3.941 5.195 4.873 3.396 5.445 4.036 3.703
P-value less than 0.001 less than 0.001 less than 0.001 less than 0.001 less than 0.001 less than 0.001 less than 0.001 less than 0.001 less than 0.001
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the observation periods. However, field trials are needed to confirm the results we
obtained in the greenhouse. Our results corroborate other studies showing that during
the hot summer months, when insect abundance is highest, both Soybeans and
Kudzu are heavily colonized by Kudzu Bugs (Suiter et al. 2010, Zhang et al. 2012).
Figure 1. Mean Kudzu Bug abundance (± standard error) per sweep of the sweep net averaged
across 10 sites for (A) adults (dark gray line) and juveniles (light gray line) and (B)
mean abundance for all life stages collected from the Oconee River Greenway in Milledgeville,
GA, in 2012.
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Our sampling at the Oconee River Greenway showed that as temperatures increased
throughout the summer, there was also an increase in insect abundance
(Fig. 1B). When adult abundance was at its peak, insects covered Kudzu stems
and leaves (S. Huskisson and K. Fogg, Georgia College, Milledgeville, GA, pers.
comm). Our results support what is currently known about the Kudzu Bug life cycle
(Ruberson et al. 2013). Adults survive the winter months by overwintering in tree
bark and on the ground in leaf litter (Ruberson et al. 2013). Adults emerge early
in the spring in search of host plants where the insects can feed and oviposit. The
first generation begins emerging in June. Adult abundance continues to increase
through the summer until it peaks in late summer (Eger et al. 2010). The insects are
Figure 2. Mean Kudzu
Bug density (±
standard error) on
Kudzu and Soybean
during feedingpreference
test, with
10 insects added to
each cage (n = 20)
containing equivalent
amounts of each
plant material; *
over a pair of bars
indicates P < 0.05.
Figure 3. Mean Kudzu
Bug density (±
standard error) on
non-inoculated and
inoculated Soybean
plants during a feeding-
preference test
with 10 insects added
to each cage (n =
20) containing one
rhizobium-inoculated
Soybean seedling
and one non-inoculated
Soybean seedling.
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2015 Vol. 14, No. 1
bivoltine (Eger et al. 2010), and we observed the second generation of juveniles
emerging in mid-September (Fig. 1A). Our sampling also found a large amount of
variation in Kudzu Bug abundance among sites, especially during peak population
densities (Fig. 1). It is possible that abiotic variation among sites—differences in
temperature or humidity levels or differences in Kudzu plant quality—contributed
to variation in insect density.
Other insects in the order Hemiptera follow similar abundance patterns. Euschitus
servus (Say) (Brown Stink Bug) exhibits seasonal dynamics in Iowa quite
similar to the dynamics exhibited by Kudzu Bugs in Georgia. Brown Stink Bugs
have 2 generations that are active in the summer months, and the adults overwinter
(Munvaneza and McPherson 1994). Light and activity are correlated for many
insect species, and many species are more active during longer photoperiods than
during shorter ones (Dingle 1968).
During our preference-choice tests, Kudzu Bug densities were always higher
on Kudzu than on Soybeans. However, this difference was only statistically significant
during the afternoon sampling period on Day 1 (Fig. 2). It is possible that
the field-collected Kudzu vines were becoming less attractive to the insects because
of wilting, which would explain why there was no difference on Day 2. This
preference for Kudzu over Soybeans on Day 1 is interesting, given that the Kudzu
samples used in this study were field-collected but the Soybeans were young seedlings
growing in pots. We would have expected that the Kudzu Bugs would prefer
the greenhouse-raised Soybeans over the field-collected Kudzu because fieldgrown
foliage has been observed to have greater leaf toughness, a higher carbon
content, higher trichome density, and lower water content than greenhouse-grown
foliage (Frye et al. 2007). In this study, we were unable to differentiate Kudzu Bug
feeding and resting behaviors on the plants. Additionally, in these experiments, we
did not record any measure of damage by herbivory because of the short timescale
and low insect densities used.
It is curious that Kudzu Bugs showed no preference between inoculated and
non-inoculated Soybeans. It has been reported that additional nitrogen supplied by
rhizobium usually improves the food quality of plants and consequently, increases
herbivore performance (Kempel et al. 2009). Other work in our laboratory has
shown that inoculation causes increased root nodulation (A. Zimmerman and C.B.
Zehnder, Georgia College, Milledgeville, GA, unpubl. data), providing evidence
that the inoculation process worked. One field study of aphids found that Soybeans
inoculated with commercially prepared rhizobium strains or given nitrogen-rich
fertilizer exhibited greater insect densities compared with those that were inoculated
with natural rhizobium strains (Dean et al. 2009). In this study, we did not measure
plant nitrogen content, so we don’t know if nitrogen concentration differed between
the inoculated and non-inoculated Soybeans. Perhaps because our plants were grown
in a commercial soil mix they were not nitrogen limited, and there was no difference
in nitrogen content between the inoculated and non-inoculated Soybeans. It is also
interesting to note that many of the insects during this part of the experiment were
found on the cage itself instead of on Soybean seedlings, especially on the first day of
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the experiment. Perhaps the longer photoperiods in October caused the Kudzu Bugs
to rest on the cage or begin searching for an overwintering location, rather than initiate
feeding during the first day of the experiment.
In summary, our study confirms previous observations of the insect’s host-plant
preferences in its native Asia and in the southeastern US. Additionally, we observed
that Kudzu Bugs infest Soybeans in the presence of Kudzu. Our observations of
increased Kudzu Bug abundance during the summer months indicate that this insect
thrives under the high temperature conditions in which Kudzu al so flourishes.
Acknowledgments
We thank P. Flamming, B. Patterson, A. Pierce, T. Quedensley, and A. Zimmerman for
laboratory and greenhouse assistance. This research was supported by the Department of
Biological and Environmental Sciences at Georgia College.
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