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COMMUNITY AND ECOSYSTEM ECOLOGY
Ground Beetle (Coleoptera: Carabidae) Assemblages in Conventional
and Diversified Crop Rotation Systems
MEGAN E. O’ROURKE,
1,2
MATT LIEBMAN,
3
AND MARLIN E. RICE
1
Environ. Entomol. 37(1): 121Ð130 (2008)
ABSTRACT Ground beetles (Coleoptera: Carabidae) are important in agro-ecosystems as generalist
predators of invertebrate pests and weed seeds and as prey for larger animals. However, it is not well
understood how cropping systems affect ground beetles. Over a 2-yr period, carabids were monitored
two times per month using pitfall traps in a conventional chemical input, 2-yr, corn/soybean rotation
system and a low input, 4-yr, corn/soybean/triticale-alfalfa/alfalfa rotation system. Carabid assem-
blages were largely dominated by a few species across all cropping treatments with Poecilus chalcites
Say comprising ⬎70% of pitfall catches in both years of study. Overall carabid activity density and
species richness were higher in the low input, 4-yr rotation compared with the conventionally
managed, 2-yr rotation. There were greater differences in the temporal activity density and species
richness of carabids among crops than within corn and soybean treatments managed with different
agrichemical inputs and soil disturbance regimes. Detrended correspondence analysis showed strong
yearly variation in carabid assemblages in all cropping treatments. The increase in carabid activity
density and species richness observed in the 4-yr crop rotation highlights the potential beneÞts of
diverse crop habitats for carabids and the possibility for managing natural enemies by manipulating
crop rotations.
KEY WORDS agro-ecology, beetle communities, biological control, generalist predators, natural
enemies
With the intensiÞcation of agricultural production
during the 20th century, agro-ecosystems have be-
come increasingly dominated by chemically intensive,
short rotation cropping systems (Pretty 1995). Con-
comitantly, many agricultural production practices
such as tillage and pesticide use have been associated
with the degradation of soil and water resources (Na-
tional Research Council 1989). One approach for mit-
igating the environmental consequences of agricul-
tural production is to diversify crop rotations. The
possible beneÞts of diversiÞed cropping systems in-
clude reduced need for inorganic nitrogen additions
when legumes are added to a rotation (Chalk 1998),
reduced soil erosion and improved soil characteristics
(Karlen et al. 1994), and reduced pest pressures (Brust
and King 1994, Kratochvil et al. 2004, Teasdale et al.
2004).
One way in which diversiÞed cropping systems
might contribute to reduced pest pressures is through
conservation of natural enemy populations. Carabids
are an important group of generalist predator natural
enemies that are commonly found in agro-ecosystems
(Kromp 1999). They have been reported to consume
a wide range of agricultural pest species including
both invertebrates and weed seeds (Toft and Bilde
2002). Carabids are also important prey species for
many vertebrates such as birds and rodents and may
contribute to the overall biotic diversity within agro-
ecosystems (Holland 2002).
Despite the importance of carabids in agroecosys-
tems, impacts of crop management practices, includ-
ing tillage and agrichemical use, on them are not well
understood. A number of studies have underscored
the importance of Þeld margins (French and Elliott
1999, Thomas and Marshall 1999) and refuges com-
posed of perennial plants (Carmona and Landis 1999,
Lee et al. 2001) for conserving carabids. However,
within the crop habitat itself, there is conßicting ev-
idence as to the consequences of tillage and pesticide
regimen on carabids. Carcamo (1995) found that total
carabid activity density in barley was higher with
conventional tillage compared with reduced tillage,
whereas Brust et al. (1986) found reduced levels of
carabid activity density in conventional versus no-till
corn and soybean. In laboratory experiments, it was
determined that the herbicide metribuzin caused no
direct mortality of Harpalus rufipes, whereas Þeld ex-
periments showed that the combined effects of me-
tribuzin and chisel plowing signiÞcantly reduced H.
rufipes activity density (Zhang et al. 1998). In exam-
ining conventional versus organic management regi-
mens, Melnychuk et al. (2003) found no signiÞcant
effects on carabid activity density or species diversity,
1
Department of Entomology, Iowa State University, Ames, IA
50011.
2
Corresponding author, e-mail: meo27@cornell.edu.
3
Department of Agronomy, Iowa State University, Ames, IA 50011.
0046-225X/08/0121Ð0130$04.00/0 䉷 2008 Entomological Society of America
whereas Carcamo et al. (1995) found higher levels of
carabid activity density and species diversity in or-
ganic systems.
In this study, the main objectives were to under-
stand how cropping systems affect carabid activity
density and community characteristics. Within a crop,
we hypothesized that management regimens using
reduced levels of fertilizers and herbicide inputs
would result in greater carabid activity density and
species richness. We also hypothesized that increasing
the diversity of crops within a rotation system would
result in increased carabid activity density and species
richness. To test these hypotheses, we compared cara-
bid assemblages in a conventionally managed corn/
soybean rotation system with a low chemical-input
corn/soybean/triticale-alfalfa/alfalfa rotation system.
Materials and Methods
Cropping Systems. Crop rotations were established
in 2002 on Clarion-Nicollet-Webster mixed loam soils
at Iowa State UniversityÕs Marsden Farm, Boone Co.,
IA. Before the cropping systems experiment, the land
had been commercially managed for corn (Zea mays
L.) and soybean (Glycine max L. Merr.) production
and planted to oat (Avena sativa L.) in 2001. The two
cropping systems compared were a 2-yr corn/soybean
rotation and a 4-yr corn/soybean/triticale (⫻Triti-
cosecale Wittmack) underseeded with alfalfa (Medi-
cago sativa L.)/alfalfa rotation. The experiment was
laid out as a randomized complete block design with
the two crops of the 2-yr rotation and the four crops
of the 4-yr rotation present every year. There were
four replicate blocks separated by ⬇15 m of mowed,
mixed grasses (mostly Festuca spp.), and each treat-
ment plot within the four blocks measured 18 by 84 m.
The two cropping systems were managed for high
yield, and the timing and quantity of inputs varied
between years depending on soil nutrient tests, Þeld
scouting, and weather conditions. Daily average tem-
peratures from July through October were 18.9 and
18.5⬚C during 2003 and 2004, respectively, compared
with an 18.6⬚C average temperature for the same pe-
riod since 1950. Total rainfall from July through Oc-
tober 2003 and 2004 was 317 and 261 mm, respectively,
compared with an average of 346 mm for the same time
period since 1950. The 2-yr system received 3.35 times
more inorganic nitrogen and 4.76 times more herbi-
cide than the 4-yr rotation (Heggenstaller and Lieb-
man 2006). However, mechanical cultivation to con-
trol weeds was greater in 4-yr corn and soybean than
2-yr corn and soybean.
Nitrogen inputs were applied to corn and triticale-
alfalfa plots. Synthetic nitrogen fertilizer was applied
to the corn phase of the 2-yr system at a rate of 150 and
110 kg N/ha in 2003 and 2004, respectively, based on
soil test results. Synthetic nitrogen fertilizer was ap-
plied to corn in the 4-yr system at rates of 55 kg N/ha
in 2003 and 70 kg N/ha in 2004, based on soil test
results, and to triticale at a rate of 30 kg N/ha in both
years. Organic N inputs were also applied to corn in
the 4-yr rotation in the form of composted manure
applied at a rate of 15 mg/ha (fresh weight).
Herbicides were applied to corn and soybean. In
2-yr corn plots, metolachlor and isoxaßutole were ap-
plied at 1.60 and 0.11 kg (AI)/ha, respectively, pre-
plant incorporated (PPI) in 2003 and preemergence
(PRE) in 2004. A postemergence (POST), broadcast
application of nicosulfuron, rimsulfuron, and mestri-
one, at 0.026, 0.013, and 0.07 kg AI)/ha, respectively,
was also made to 2-yr corn plots in 2003. PPI and PRE
herbicides were not applied to 4-yr corn plots. How-
ever, POST, banded applications of nicosulfuron, rim-
sulfuron, and mestrione at 0.013, 0.007, and 0.035 kg
(AI)/ha were made in both 2003 and 2004 (materials
were applied to only 50% of surface area; reported
values indicate dosages to total plot area). Weeds were
controlled in 2-yr soybean in 2003 with PPI metola-
chlor and in 2004 with PRE metolachlor applied at 1.60
kg (AI)/ha both years. In 2003, the 2-yr soybean treat-
ment was also treated with POST broadcast bentazon
and clethodim applied at 1.12 and 0.11 kg (AI)/ha,
respectively. Chemical weed control in 4-yr soybean
included PPI metolachlor in 2003 and PRE metola-
chlor in 2004 applied at 1.60 kg (AI)/ha in both years.
The 4-yr soybean treatment also received POST
banded ßumiclorac at 0.03 kg (AI)/ha in 2003 and
POST banded bentazon at 0.56 kg (AI)/ha in 2004
(dosage to total plot area).
The 2-yr rotation was chisel plowed every other
year after corn harvest, whereas the 4-yr rotation was
moldboard plowed in the fall after the alfalfa phase
and chisel plowed after the corn phase of the rotation.
In 2-yr corn, weeds were rotary hoed once in 2003, but
no mechanical weed control was used in 2004. Four-
year corn received one rotary hoeing and two inter-
row cultivations in 2003 and one rotary hoeing and one
inter-row cultivation in 2004. No mechanical weed
control was used in 2-yr soybean, but 4-yr soybean
received one rotary hoeing and one inter-row culti-
vation in 2003, and one rotary hoeing and two inter-
row cultivations in 2004. Weeds were mechanically
controlled in triticale-alfalfa plots, receiving one stub-
ble mowing of the underseeded alfalfa in August 2003
and 2004. Alfalfa plots were harvested three times in
2003 and four times in 2004.
Sampling. Carabid activity density was monitored
using pitfall traps. The abundance of adult beetles
collected by pitfall traps reßects both the activity of
adult carabids and their propensity for moving into
traps and their population density in the surrounding
environment (Thiele 1977, Southwood 1978). Traps
were 1-liter plastic cups buried ßush to the soil surface
containing a 20% propylene glycol preservative solu-
tion. Within each treatment plot, there were four
pitfall traps placed at least 5 m from adjacent plots and
⬇18 m from each other and the grassy plot borders. In
total, there were 96 pitfall traps in the experimental
area (4 per plot ⫻ 6 treatment plots ⫻ 4 blocks).
Pulsating sampling was used to collect carabids, where
pitfall traps were open for 5 consecutive d, approxi-
mately every 2 wk (Sapia et al. 2006). Pulsating sam-
pling minimized the time traps were open in the rain
122 E
NVIRONMENTAL ENTOMOLOGY Vol. 37, no. 1
and allowed for trap retrieval when tractors were in
the Þeld. During 2003, traps were opened for nine 5-d
periods between 23 May and 7 October. During 2004,
traps were opened for eleven 5-d periods between 11
May and 6 October. On retrieval in the Þeld, pitfall
trap contents were sieved through 1-mm mesh, placed
in sealable plastic bags, and stored in a freezer until
sorting. Carabid species were determined according
to Lindroth (1969) and Bousquet and Larochelle
(1993). Only adult beetles were identiÞed and re-
corded in this study. A voucher specimen collection
was deposited in Iowa State UniversityÕs Department
of Entomology Insect Museum.
Statistical Analysis. Fisher exact tests were used to
determine whether species trapped in only one treat-
ment were more likely to be found in the triticale-
alfalfa and alfalfa treatments compared with the 2- and
4-yr corn and soybean treatments. Fisher exact tests
were also used to determine whether species collected
in only one treatment were more likely to be found in
the 2-yr corn and soybean treatments than in the 4-yr
corn, soybean, triticale-alfalfa, and alfalfa treatments
(Sokal and Rohlf 1995).
Four indices were calculated to evaluate cropping
system effects on carabid beetle assemblages: activity
density, species richness, SimpsonÕs diversity index,
and SimpsonÕs evenness index. Activity density was
the total number of carabids trapped. Species richness
was the total number of carabid species trapped. Simp-
sonÕs diversity index indicates the probability of ran-
domly picking two organisms from a sample that are
different species and was calculated as 1 ⫺ 冱p
i
2
where
p
i
is the proportion of species i in the community.
SimpsonÕs evenness index ranges from 0 to 1 and in-
creases as the proportion of each species in a sample
nears equality; it was calculated as s/冱p
i
2
, where s is
the total number of species and p
i
is the proportion of
species i in the community (Krebs 1999). SigniÞcant
differences in assemblage indices among treatments
were determined using analysis of variance (ANOVA),
with year, crop treatment, and crop treatment by year
interactions as Þxed effects and block as a random
effect (PROC MIXED; SAS Institute 2002). Activity
density and species richness were ln(x ⫹ 1) trans-
formed. Multiple, pairwise treatment comparisons
were all Tukey adjusted. Overall differences between
the 2- and 4-yr crop rotations were evaluated using
contrast statements.
Detrended correspondence analysis (DCA) was
conducted using the statistical software PC-ORD ver-
sion 4.0 (McCune and Mefford 1999) to evaluate vari-
ations in carabid assemblages among cropping treat-
ments and between 2003 and 2004. The nine most
abundant beetle species, for which at least 50 speci-
mens were collected over 2 yr, were treated as sepa-
rate response variables, and all other beetles species
were added together in the category other. DCA was
conducted with a rescaling threshold of 0.0, and axes
were detrended using 30 segments. In each analysis,
the Þrst two axes were interpreted, and the proportion
of variance explained by those axes was calculated
from the correlations between
2
distances among
samples in the original space and the Euclidean dis-
tances in ordination space (McCune and Mefford
1999).
Differences in individual species responses to crop-
ping treatments were evaluated separately over 2003
and 2004 using ANOVA with crop treatment as a Þxed
factor, sample date as a repeated measure with com-
pound symmetry covariance structure (samples from
two consecutive dates are not assumed to be more
correlated than samples on two random dates), and
block as a random factor (PROC MIXED; SAS Insti-
tute 2002). Activity density of each beetle species was
either ln(x ⫹ 1) transformed or sqrt(x) transformed,
depending on which transformation caused data to
appear more normally distributed. Probability values
for posthoc multiple comparisons among cropping
treatments were obtained using Tukey pairwise ad-
justments.
Results
Phenology. In both 2003 and 2004, the temporal pat-
tern of carabid activity density was more similar within
crops than among crops, despite differences in 2- and
4-yr rotation management. In 2- and 4-yr corn, carabid
activity density peaked in mid-June and fell in early July
when the canopy had Þlled in and the corn was entering
the early silking phase of development (Figs. 1, C2 and
C4, and 2, C2 and C4). In 2- and 4-yr soybean, carabid
activity density was high in mid-June and did not reach
consistent lows until early August when the soybean
canopy had Þlled in (Figs. 1, S2 and S4, and 2, S2 and S4).
In triticale-alfalfa plots, the temporal pattern of carabid
activity density was distinctive in 2003, with more cara-
bid species caught early in the season compared with the
other cropping treatments. The drop in carabid activity
density in triticale-alfalfa, in late July, corresponded to
triticale harvest (Figs. 1, T4, and 2, T4). In alfalfa, carabid
activity density remained higher, later in the season, than
in other crops. Carabid catches were low in alfalfa after
harvest, when the canopy was very open, peaked be-
tween alfalfa cuttings when the canopy regrew, and
declined before the next harvest (Figs. 1, A4, and 2, A4).
Assemblage. A total of 3,168 carabid beetles, repre-
senting 21 species, was collected in 2003. During 2004,
a total of 3,556 carabids of 32 species was collected.
The dominant carabid sampled was Poecilus chalcites,
comprising ⬎70% of pitfall catches in both 2003 and
2004. According to Bousquet and Larochelle (1993),
the single specimen of Anisodactylus caenus collected
in 2004 in the triticale-alfalfa treatment represented
the Þrst time this species had been collected in Iowa.
Of the nine species of carabids captured in just one
cropping treatment in 2003, they were just as likely to
be trapped in the four corn and soybean treatments as
the two triticale-alfalfa and alfalfa treatments (P ⬎
0.50) and were just as likely to be trapped in 2-yr corn
and soybean as 4-yr corn, soybean, triticale-alfalfa, and
alfalfa rotation treatments (P ⬎ 0.50). However, in
2004, the 13 species trapped in only one treatment
were encountered more often in the two triticale-
alfalfa and alfalfa treatments than the four corn and
February 2008 OÕR
OURKE ET AL.: GROUND BEETLE ASSEMBLAGES AND CROPPING SYSTEMS 123
soybean treatments (P ⬍ 0.01) but were not more
likely to be trapped in 4-yr than 2-yr rotation treat-
ments (P ⫽ 0.16; Table 1).
Different rotation management regimens did not
signiÞcantly affect the activity density, species rich-
ness, SimpsonÕs evenness index, or SimpsonÕs diversity
0
5
10
15
20
19-May 19-Jun 19-Jul 19-Aug 19-Sep
0
5
10
15
20
0
5
10
15
20
0
0
5
10
15
20
19-May 19-Jun 19-Jul 19-Aug 19-Sep
C2
C4
T4 A4
5
10
15
20
S2
0
5
10
15
20
S4
rotary hoe or inter-row cultivation
herbicide application
A4: alfalfa harvest; T4: triticale harvest
Poecilus chalcites
Other
Fig. 1. Temporal patterns of adult P. chalcites, and the sum of all other adult carabid species captured per pitfall trap during
2003 in Boone Co., IA, in six crop ⫻ rotation system treatments (C2) corn, 2-yr; (S2) soybean, 2-yr; (C4) corn, 4-yr; (S4)
soybean, 4-yr; (T4) triticale-alfalfa, 4-yr; (A4) alfalfa, 4-yr. Error bars represent SE of total beetle abundance at each sampling
date.
124 ENVIRONMENTAL ENTOMOLOGY Vol. 37, no. 1
0
5
10
15
20
25
30
11-May 11-Jun 11-Jul 11-Aug 11-Sep
0
5
10
15
20
25
30
0
5
10
15
20
25
30
0
5
10
15
20
25
30
0
5
10
15
20
25
30
0
5
10
15
20
25
30
11-May 11-Jun 11-Jul 11-Aug 11-Sep
S2
C4
A4
T4
S4
C2
rotary hoe or inter-row cultivation
herbicide application
A4: alfalfa harvest; T4: triticale harvest
Poecilus chalcites
Other
Fig. 2. Temporal patterns of adult P. chalcites, and the sum of all other adult carabid species captured per pitfall trap
during 2004 in Boone Co., IA, in six crop ⫻ rotation system treatments: (C2) corn, 2-yr; (S2) soybean, 2-yr; (C4) corn,
4-yr; (S4) soybean, 4-yr; (T4) triticale-alfalfa, 4-yr; (A4) alfalfa, 4-yr. Error bars represent SE of total beetle abundance
at each sampling date.
February 2008 OÕROURKE ET AL.: GROUND BEETLE ASSEMBLAGES AND CROPPING SYSTEMS 125
index in the different rotation treatments of corn or
soybean in 2003 and 2004. However, when contrasts
were made between the 2- and 4-yr cropping systems
over the 2 yr of the experiment, there was signiÞcantly
greater activity density (t ⫽ 2.71, df ⫽ 33, P ⫽ 0.01) and
number of species (t ⫽ 3.42, df ⫽ 33, P ⫽ 0.002) per
year in the 4-yr system than in the 2-yr system. How-
ever, carabid evenness was greater in the 2-yr than the
4-yr system (t ⫽ 2.41, df ⫽ 33, P ⬍ 0.05), largely
because of the overall increased activity density of P.
chalcites in the 4-yr crop rotation. There were no
signiÞcant differences in SimpsonÕs diversity between
the 2- and 4-yr systems (Table 2).
DCA of beetle assemblages in 2003 indicated that
triticale-alfalfa treatments separated from the other
cropping treatments along the Þrst DCA axis charac-
terized by A. sanctaecrucis, H. pensylvanicus, H. her-
bivagus, and S. comma (Fig. 3). In 2004, both triticale-
alfalfa and alfalfa generally clustered toward H.
pensylvanicus, H. herbivagus, P. lucublandus, and other
less common species, whereas corn and soybean treat-
ments tended to cluster more toward A. comma, P.
pensylvanicus, A. sactaecrucis, and P. permundus (Fig.
4). For 2003 data, the Þrst axis explained 59% of carabid
assemblage variance, whereas the second axis ex-
plained an additional 20%. For 2004 data, the Þrst DCA
axis explained 62% of variance, whereas the second
axis explained an additional 19%.
DCA showed that carabid assemblages were differ-
ent between 2003 and 2004 across all cropping treat-
ments. In 2003, B. rapidum, H. pensylvanicus, H. her-
bivagus, and S. comma were generally more common
than in 2004, when S. quadriceps, P. lucublandus, and
P. permundus were more common. The Þrst DCA axis
captured 26% of the variance in beetle assemblage,
whereas the second axis captured an additional 52% of
variation (Fig. 5).
Species-Specific Effects. When the activity densities
of individual species of carabid beetles in 2003 and
2004 were compared, little effect of rotation manage-
ment regimen within a crop was detected. During 2003
and 2004, there were no differences in Tukey pairwise
comparisons of individual speciesÕ activity density be-
Table 1. Relative abundance of ground beetle species collected
in 2003 and 2004 at Iowa State University’s Marsden Farm, Boone
Co., IA
Species
Percent total
2003
a
2004
b
Poecilus chalcites Say 70.1 71.8
Stenolophus comma F. 9.4 1.9
Harpalus pensylvanicus DeGeer 5.1 0.5
Poecilus lucublandus Say 2.3 9.0
Harpalus herbivagus Say 2.0 0.5
Anisodactylus sanctaecrucis F. 1.6 1.3
Bembidion rapidum LeConte 1.2 0.4
Scarites quadriceps Chaudoir 1.2 6.3
Agonum placidum Say 1.1 0.3
Pterostichus permundus Say 1.0 4.4
Clivina bipustulata F. 0.9 0.5
Clivina impressifrons LeConte 0.8 0.2
Stenolophus ochropezus Say 0.8 ⬍0.1 A4
Harpalus calignosus F. 0.5 0.1
Anisodactylus rusticus Say 0.3 0.2
Cratacanthus dubius Palisot de
Beauvois
0.3 0.0
Chlaenius impunctifrons Say 0.3 0.1
Galerita janus F. 0.2 0.1 T4
Cyclotrachelus sodalis LeConte 0.2 1.1
Agonum cupripenne Say 0.2 0.1
Anisodactylus harrisii LeConte 0.1 0.2
Amara carinata LeConte 0.1 T4 0.5
Amara impuncticollis Say 0.1 A4 ⬍0.1 T4
Harpalus erythropus Dejean 0.1 0.0
Amara aeneopolita Casey ⬍0.1 T4 ⬍0.1 A4
Anisodactylus merula Germar ⬍0.1 C2 ⬍0.1 S2
Pterostichus commutabilis
Motschulsky
⬍0.1 C4 ⬍0.1 A4
Pterostichus stygicus Say ⬍0.1 C4 ⬍0.1 A4
Calosoma externum Say ⬍0.1 C4 0.0
Amara obesa Say ⬍0.1 S4 0.0
Lebia viridis Say ⬍0.1 T4 0.0
Chlaenius brevilabris LeConte 0.0 ⬍0.1 T4
Discoderus parallelus Haldeman 0.0 ⬍0.1 T4
Anisodactylus ovularis Casey 0.0 ⬍0.1 T4
Chlaenius tomentosus Say 0.0 ⬍0.1 T4
Anisodactylus caenus Say 0.0 ⬍0.1 T4
Chlaenius lithophilus Say 0.0 ⬍0.1 A4
Treatment abbreviations following data represent instances where
a species was trapped exclusively in one treatment: (C2) corn-2yr,
(S2) soybean-2yr, (C4) corn-4yr, (S4) soybean-4yr. (T4) triticale-
4yr, (A4) alfalfa-4yr.
a
A total of 3,168 individuals collected over nine sampling dates.
b
A total of 3,556 individuals collected over 11 sampling dates.
Table 2. Activity density, species richness, Simpson’s evenness index, and Simpson’s diversity index estimates for adult carabid beetles
in each cropping treatment and crop rotation in 2003 and 2004, Boone Co., IA
Activity
density
a
Species
richness
a
SimpsonÕs
evenness
SimpsonÕs
diversity
Cropping treatment
Corn, 2-yr 16.79 ⫾ 1.94a 8.13 ⫾ 0.61a 0.37 ⫾ 0.04b 0.62 ⫾ 0.05c
Corn, 4-yr 28.34 ⫾ 2.08ab 9.88 ⫾ 0.91ab 0.24 ⫾ 0.03ab 0.53 ⫾ 0.04bc
Soybean, 2-yr 37.22 ⫾ 4.47b 8.38 ⫾ 0.68a 0.20 ⫾ 0.05a 0.29 ⫾ 0.05a
Soybean, 4-yr 44.31 ⫾ 8.15b 9.25 ⫾ 0.59ab 0.18 ⫾ 0.02a 0.35 ⫾ 0.05ab
Triticale-alfalfa, 4-yr 36.97 ⫾ 7.64ab 13.63 ⫾ 1.72b 0.26 ⫾ 0.04ab 0.61 ⫾ 0.07c
Alfalfa, 4-yr 47.69 ⫾ 9.39b 11.63 ⫾ 0.65ab 0.18 ⫾ 0.02a 0.46 ⫾ 0.07abc
Crop rotation
2-Yr 27.01 ⫾ 2.90A 8.25 ⫾ 0.53A 0.28 ⫾ 0.03B 0.46 ⫾ 0.04A
4-Yr 39.33 ⫾ 3.65B 11.09 ⫾ 0.72B 0.21 ⫾ 0.01A 0.49 ⫾ 0.02A
Values are cup per year ⫾ SE.
Cropping treatment or crop rotation means followed by same letter within columns are not signiÞcantly different (P ⬎ 0.05); Tukey pairwise
comparison test.
a
Activity density and species richness comparisons performed on ln(x ⫹ 1)-transformed data.
126 ENVIRONMENTAL ENTOMOLOGY Vol. 37, no. 1
tween the 2- and 4-yr rotation corn treatments (Table
3). Between 2- and 4-yr rotation soybean, there was
only one instance when the activity density of a cara-
bid species was signiÞcantly different. In 2004, pitfall
catches of S. quadriceps were 2.24 times higher in the
4-yr compared with the 2-yr rotation soybean (t ⫽
2.96, df ⫽ 194, P ⫽ 0.04). This difference was not
detected in 2003 but may have been caused by the
overall low catches of S. quadriceps in 2003, making it
difÞcult to detect the effects of management regimen
(Table 3).
Among all six cropping treatments, certain species
of carabid beetles showed uniquely high patterns of
activity density in the triticale-alfalfa and alfalfa treat-
ments. In 2003, there were signiÞcantly more S.
comma, A. sanctaecrucis, H. herbivagus, and other bee-
tles collected in the triticale-alfalfa treatment com-
pared with any other treatment (P ⬍ 0.05). In 2004,
there were signiÞcantly more P. lucublandus and H.
herbivagus collected in the alfalfa treatment compared
with other treatments (P ⬍ 0.05; Table 3).
Discussion
Poecilus chalcites was the dominant species of adult
carabid encountered in this study, comprising ⬎70%
of the beetles captured in both 2003 and 2004. P.
chalcites can consume a large variety of soft-bodied
insects of economic importance (Larochelle and
Lariviere 2003) and is common in agricultural Þelds of
the midwestern United States (Kirk 1971, Esau and
Peters 1975, Best and Beegle 1977, Best et al. 1981,
Wiedenmann et al. 1992). The Þve most abundant
adult carabid species sampled comprised ⬇85% of
catches in both years. This result agrees with a world-
wide review by Luff (2002) of 119 datasets of Cara-
bidae in agricultural habitats where the Þve most
abundant species averaged 84% of total pitfall trap
captures. However, compared with natural habitats,
this dominance structure is highly skewed and has
been attributed to high levels of disturbances in ag-
ricultural production, including crop harvest and till-
A4
A4
A4
A4
C2
C2
C2
C2
C4
C4
C4
C4
S2
S2
S2
S2
S4
S4
S4
S4
T4
T4
T4
T4
PCH
PLU
SCO
SQU
PPE
HPE
ASA
HHE
BRA
OTH
Axis 1
Axis 2
Fig. 3. First two axes of detrended correspondence anal-
ysis of adult carabid assemblages in four replicate blocks of
six cropping treatments in 2003. C2, corn, 2-yr; S2, soybean,
2-yr; C4, corn, 4-yr; S4, soybean, 4-yr; T4, triticale-alfalfa, 4-yr;
A4, alfalfa, 4-yr. ASA, A. sanctaecrucis; BRA, B. rapidum; HHE,
H. herbivagus; HPE, H. pensylvanicus; OTH, sum of all other
species with ⬍50 specimens collected; PCH, P. chalcites;
PLU, P. lucublandus; PPE, P. permundus; SCO, S. comma;
SQU, S. quadriceps.
A4
C2
C4
S2
S4
T4
A4
C2
C4
S2
S4
T4
A4
C2
C4
S2
S4
T4
A4
C2
C4
S2
S4
T4
PCH
PLU
ACO
SQU
PPE
HPE
ASA
HHE
BRA
OTH
Axis 1
Axis 2
Fig. 4. First two axes of detrended correspondence anal-
ysis of adult carabid assemblages in four replicate blocks of
six cropping treatments in 2004. C2, corn, 2-yr; S2, soybean,
2-yr; C4, corn, 4-yr; S4, soybean, 4-yr; T4, triticale-alfalfa, 4-yr;
A4, alfalfa, 4-yr. ASA, A. sanctaecrucis; BRA, B. rapidum; HHE,
H. herbivagus; HPE, H. pensylvanicus; OTH, sum of all other
species with ⬍50 specimens collected; PCH, P. chalcites;
PLU, P. lucublandus; PPE, P. permundus; SCO, S. comma;
SQU, S. quadriceps.
February 2008 OÕROURKE ET AL.: GROUND BEETLE ASSEMBLAGES AND CROPPING SYSTEMS 127
age, which are intolerable for many carabid species
(Thiele 1977).
The strong effects of crop on carabid assemblage
and activity density seen in this study support the
results of numerous other researchers (Tonhasca
1993, Ellsbury et al. 1998, Zhang et al. 1998, Honek and
Jarosik 2000, Ward and Ward 2001, Butts et al. 2003,
Melnychuk et al. 2003, Witmer et al. 2003). Crops
likely affect carabids through modiÞcation of micro-
climatic factors, such as temperature and humidity,
and through disturbance factors such as harvest and
tillage schedules (Thiele 1977, Holland 2002). Similar
crop phenology and management may explain why
the temporal activity density and assemblages of cara-
bids were relatively similar in corn and soybean but
dissimilar in those crops compared with triticale-al-
falfa and alfalfa treatments.
In addition to differences in carabid assemblages
among crops, results of this study also emphasized
yearly differences in carabid activity density. Of the
nine most abundant species trapped in this study, six
species, including S. comma, H. pensylvanicus, P. lucu-
blandus, H. herbivagus, S. quadriceps, and P. permun-
dus, were variably abundant between years. Other
studies have also found high variability in carabid
activity density among years (French and Elliott 1999,
Irmler 2003, French et al. 2004). Over the course of 9
yr of pitfall trapping in one Þeld, Irmler (2003) found
signiÞcant correlations between the activity density of
approximately one half the species examined with
either yearly precipitation or temperature. Weather
variation may have been a factor in the current study
with ⬇2.5 cm more rainfall per month between April
and September in 2004 than in 2003 and daily high
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
XX
X
X
X
X
X
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
PCH
PLU
ACO
SQU
PPE
HPE
ASA
HHE
BRA
OTH
Axis 1
Axis 2
Fig. 5. First two axes of detrended correspondence
analysis of adult carabid assemblages in 2003 (X) and 2004
(O). ASA, A. sanctaecrucis; BRA, B. rapidum; HHE, H.
herbivagus; HPE, H. pensylvanicus; OTH, sum of all other
species with ⬍50 specimens collected; PCH, P. chalcites;
PLU, P. lucublandus; PPE, P. permundus; SCO, S. comma;
SQU, S. quadriceps.
Table 3. Carabid species’ responses to crop rotation systems in 2003 and 2004 at Iowa State University’s Marsden Farm, Boone Co., IA
Species
a
Corn, 2-yr Corn, 4-yr
Soybean,
2-yr
Soybean,
4-yr
Triticale-
alfalfa, 4-yr
Alfalfa, 4-yr
2003
Anisodactylus sanctaecrucis 0.1 ⫾ 0.1a 0.1 ⫾ 0.1a 0.0 ⫾ 0.0a 0.2 ⫾ 0.1a 2.5 ⫾ 1.0b 0.3 ⫾ 0.1a
Bembidion rapidum
b
0.0 ⫾ 0.0a 0.0 ⫾ 0a 0.8 ⫾ 0.4ab 0.1 ⫾ 0.1a 0.7 ⫾ 0.3ab 0.9 ⫾ 0.2b
Harpalus herbivagus 0.1 ⫾ 0.1a 0.1 ⫾ 0.1a 0.1 ⫾ 0.1a 0.4 ⫾ 0.3a 2.8 ⫾ 0.5b 0.4 ⫾ 0.2a
Harpalus pensylvanicus 1.2 ⫾ 0.4ab 1.9 ⫾ 0.6ab 0.6 ⫾ 0.2a 1.0 ⫾ 0.2a 3.3 ⫾ 0.3b 2.3 ⫾ 1.1ab
Poecilus chalcites 10.6 ⫾ 2.5a 17.2 ⫾ 0.6ab 36.2 ⫾ 5.8bc 27.3 ⫾ 6.2bc 14.8 ⫾ 3.9ab 32.8 ⫾ 8.6c
Poecilus lucublandus 0.8 ⫾ 0.2 1.5 ⫾ 0.6 0.6 ⫾ 0.3 0.3 ⫾ 0.2 0.6 ⫾ 0.2 0.9 ⫾ 0.4
Pterostichus permundus 0.0 ⫾ 0 0.8 ⫾ 0.5 0.9 ⫾ 0.9 0.1 ⫾ 0.1 0.1 ⫾ 0.1 0.1 ⫾ 0.1
Scarites quadriceps 0.1 ⫾ 0.1 0.9 ⫾ 0.3 0.2 ⫾ 0.1 0.3 ⫾ 0.1 0.6 ⫾ 0.2 0.2 ⫾ 0.1
Stenolophus comma
b
2.3 ⫾ 0.4a 2.4 ⫾ 0.5a 1.5 ⫾ 0.5a 1.7 ⫾ 0.3a 10.1 ⫾ 4.6b 0.6 ⫾ 0.2a
Other
c
1.1 ⫾ 0.1a 1.5 ⫾ 0.4a 1.7 ⫾ 0.2a 2.0 ⫾ 0.5a 3.6 ⫾ 0.6b 2.1 ⫾ 0.6a
2004
Anisodactylus sanctaecrucis 0.9 ⫾ 0.5 1.2 ⫾ 0.7 0.2 ⫾ 0.1 0.3 ⫾ 0.1 0.1 ⫾ 0.1 0.4 ⫾ 0.1
Bembidion rapidum
b
0.0 ⫾ 0.0 0.0 ⫾ 0.0 0.0 ⫾ 0.0 0.0 ⫾ 0.0 0.8 ⫾ 0.5 0.1 ⫾ 0.1
Harpalus herbivagus 0.0 ⫾ 0.0a 0.0 ⫾ 0.0a 0.1 ⫾ 0.1a 0.1 ⫾ 0.1a 0.1 ⫾ 0.1a 0.8 ⫾ 0.4b
Harpalus pensylvanicus 0.1 ⫾ 0.1 0.1 ⫾ 0.1 0.1 ⫾ 0.1 0.1 ⫾ 0.1 0.4 ⫾ 0.1 0.3 ⫾ 0.2
Poecilus chalcites 7.1 ⫾ 1.5a 19.4 ⫾ 2.1ab 27.4 ⫾ 7.3b 45.8 ⫾ 14.8b 26.7 ⫾ 13.3b 34.0 ⫾ 18.0b
Poecilus lucublandus 2.2 ⫾ 1.0a 0.9 ⫾ 0.1a 0.7 ⫾ 0.3a 1.1 ⫾ 0.5a 2.2 ⫾ 0.9a 12.9 ⫾ 3.4b
Pterostichus permundus
b
2.9 ⫾ 1.5b 3.2 ⫾ 1.7b 0.6 ⫾ 0.3ab 2.4 ⫾ 0.3b 0.1 ⫾ 0.1a 0.6 ⫾ 0.3ab
Scarites quadriceps 1.5 ⫾ 0.4a 2.1 ⫾ 0.7a 1.9 ⫾ 0.4a 4.3 ⫾ 1.3b 1.6 ⫾ 0.5a 2.7 ⫾ 0.8ab
Stenolophus comma
b
0.4 ⫾ 0.2ab 2.4 ⫾ 0.7b 0.4 ⫾ 0.3ab 0.3 ⫾ 0.1a 0.5 ⫾ 0.2ab 0.3 ⫾ 0.2a
Other 0.8 ⫾ 0.3ab 1.0 ⫾ 0.4ab 0.6 ⫾ 0.3a 0.9 ⫾ 0.3ab 2.4 ⫾ 1.0bc 2.7 ⫾ 1.0c
Values are mean no. cup per plot ⫾ SE.
Means followed by same letter or without letters within rows are not signiÞcantly different (P ⬎ 0.05); Tukey pairwise comparison test.
a
Statistcs performed on ln(x ⫹ 1)-transformed data unless indicated by
b
for speciesÕ data that were sqrt(x) transformed.
c
Other refers to the sum of all carabid species where ⬍50 specimens were collected over 2003 and 2004.
128 ENVIRONMENTAL ENTOMOLOGY Vol. 37, no. 1
temperatures averaging 5.5⬚C cooler in 2004 during
the warmest summer month of August (Midwest Re-
gional Climate Center 2005).
The small effect of reduced levels of fertilizer and
herbicide applications on carabids was in contrast to
our original hypothesis and the Þndings of other au-
thors that reduced chemical inputs would lead to in-
creased carabid activity density and species richness
(Fan et al. 1993, Carcamo et al.1995). For example,
Carcamo et al. (1995) found signiÞcantly higher ac-
tivity density and species richness of carabids in an
organic versus conventionally managed crop rotation
where the main treatment differences were nitrogen
and herbicide applications in the conventional rota-
tion. One possible explanation for not seeing a greater
effect of management in our study is that Þeld plots
were not large enough (18 by 84 m) compared with
the dispersal ability of carabids (Wallin and Ekbom
1988), allowing beetles to colonize plots from Þeld
margins. Another explanation is that the increased soil
disturbance to control weeds in the 4-yr corn and
soybean negated any beneÞt for carabids of reduced
herbicide and inorganic fertilizer inputs. It is also
possible that differences between 2- and 4-yr corn and
soybean treatments will develop over time as the ro-
tation system progresses for more years and differ-
ences in soil characteristics develop (Grandy et al.
2006).
In this study, carabid activity density and species
richness were higher in triticale-alfalfa and alfalfa
plots than in corn and soybean plots. Activity den-
sity and species richness were also generally higher
in the 4-yr rotation than in the 2-yr rotation, because
of the incorporation of triticale-alfalfa and alfalfa
crops into the rotation (Table 2). This supports our
original idea that increasing the diversity of crops in
a rotation may support a greater number of carabid
species. Species richness was enhanced, in partic-
ular, by species only trapped a few times. In a study
of carabids in a variety of crops in the Netherlands,
Booij (1994) also found that species richness was
higher in crops with early and persistent ground
cover. These results indicate that perennial crops
such as alfalfa, and crops that form a canopy early
in the growing season, such as triticale, may provide
important refuges for carabid biodiversity without
taking agricultural land out of production.
In addition to emphasizing the importance of crop
habitat for supporting carabid populations and the
value of perennial crops for conserving species, results
of this study have also emphasized the relative toler-
ance of carabids to noninsecticidal management prac-
tices such as herbicides, fertilizers, and mechanical
weed control. However, further research over a
broader geographic region will be necessary to test the
robustness of these conclusions, which may depend on
the underlying composition of carabid species in a
region. Studies investigating carabid dispersal will
greatly aid in understanding the scale at which results
of this and other carabid studies are applicable; mark-
recapture and radio-telemetry have indicated that
carabids are capable of moving tens of meters a day
(Best et al. 1981, Wallin and Ekbom 1988), and ßight
capacity among species is highly variable (Lindroth
1969). It will also be important to further study the
factors structuring carabid assemblages across land-
scapes because it seems that the dominance structure
of carabid assemblages can vary widely, even in similar
habitats and over small geographic areas (Kirk 1971,
1975, Irmler 2003).
Acknowledgments
This research was funded by USDA NRI Grant 02-35320-
12175 and the Entomology and Agronomy Departments
and the Plant Sciences Institute at Iowa State University.
We thank K. Larsen for invaluable assistance in identifying
carabid species, F. Menalled, P. Westerman, D. Sundberg,
and A. Heggenstaller for ideas and assistance in collecting
samples, and many summer employees who helped to
collect data.
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Received for publication 23 December 2006; accepted 16
October 2007.
130 ENVIRONMENTAL ENTOMOLOGY Vol. 37, no. 1
