Andropogon bicornis (Poales, Poaceae): A Hibernation Site for Pentatomoidea (Hemiptera: Heteroptera) in a Rice-Growing Region of Southern Brazil

Abstract

Tussocks of Andropogon bicornis (Poaceae) make up a significant part of the landscape of the rice-growing region of south Brazil. However, little is known about their role in maintaining insect diversity in anthropized regions. We tested the hypothesis that A. bicornis is a hibernation site for Pentatomoidea (Hemiptera: Heteroptera) by analyzing the composition, structure, and diversity of pentatomoid assemblages over the course of a year. A total of 208 tussocks were removed at fortnightly intervals from April 2010 to March 2011. We collected 3,423 pentatomoid specimens belonging to 22 species distributed in 13 genera of three families, Pentatomidae, Scutelleridae, and Thyreocoridae. The most common species was Tibraca limbativentris Stål, the main rice pest in southern Brazil, followed by Oebalus ypsilongriseus (De Geer) and Edessa meditabunda (Fabricius). Abundance and species richness were the lowest in January, February, and March and the highest in July, August, and September. A combination of high species diversity observed during the colder months, including several unrelated to rice, and the absence of immature specimens in the tussocks strengthens the hypothesis that A. bicornis is a hibernation site for pentatomoids in the region.

Full text

ECOLOGY, BEHAVIOR AND BIONOMICS
Andropogon bicornis (Poales, Poaceae): A Hibernation Site
for Pentatomoidea (Hemiptera: Heteroptera) in a Rice-Growing Region
of Southern Brazil
JT KLEIN
1
,LRREDAELLI
1
,ABARCELLOS
2
1
Programa de Pós-graduação em Biologia Animal, Univ Federal do Rio Grande do Sul, Porto Alegre, RS, Brasil
2
Museu de Ciências Naturais, Fundação Zoobotânica do Rio Grande do Sul, Porto Alegre, RS, Brasil
AbstractKeywords
Agroecosystem, Pentatomidae, refuge,
tussocks
Correspondence
JT Klein, Programa de Pós-graduação em
Biologia Animal, Univ Federal do Rio
Grande do Sul, Av. Bento Gonçalves,
9500, 91501-970, Porto Alegre, RS, Brasil;
joanatartariklein@yahoo.com.br
Edited by Antonio R Panizzi –Embrapa Trigo
Received 20 April 2012 and accepted 31
January 2013
Published online 7 March 2013
*Sociedade Entomológica do Brasil 2013
Tussocks of Andropogon bicornis (Poaceae) make up a significant part of
the landscape of the rice-growing region of south Brazil. However, little is
known about their role in maintaining insect diversity in anthropized
regions. We tested the hypothesis that A. bicornis is a hibernation site
for Pentatomoidea (Hemiptera: Heteroptera) by analyzing the composi-
tion, structure, and diversity of pentatomoid assemblages over the course
of a year. A total of 208 tussocks were removed at fortnightly intervals
from April 2010 to March 2011. We collected 3,423 pentatomoid speci-
mens belonging to 22 species distributed in 13 genera of three families,
Pentatomidae, Scutelleridae, and Thyreocoridae. The most common spe-
cies was Tibraca limbativentris Stål, the main rice pest in southern Brazil,
followed by Oebalus ypsilongriseus (De Geer) and Edessa meditabunda
(Fabricius). Abundance and species richness were the lowest in January,
February, and March and the highest in July, August, and September. A
combination of high species diversity observed during the colder months,
including several unrelated to rice, and the absence of immature speci-
mens in the tussocks strengthens the hypothesis that A. bicornis is a
hibernation site for pentatomoids in the region.
Introduction
The role of grass tussocks as shelter for invertebrates has
long been emphasized (Pearce 1948, Luff 1966). Vegetation
structure at the edges of agroecosystems may play an
important role in insect survival during cold periods
(Dennis et al 1994) in terms of providing a favorable mi-
croclimate and serving as hibernation sites (Geiger et al
2009, Helden et al 2010). Tussocks form dense bushes and
are easily distinguishable from the surrounding vegetation
by the proximity between their leaves and stems, accumu-
lation of dry foliage around the base, and distance from
nearby grasses (Luff 1965).
Tussocks of Andropogon bicornis (Poaceae) are com-
monly distributed at the edges of fields, roadsides, and
remaining fragments of forest in Rio Grande do Sul, which
has extensive irrigated rice cultivation. This grass, known as
West Indian foxtail, is native to the Americas and prefer-
entially inhabits humid places throughout the year
(Kissmann and Groth 2000). As such, tussocks represent
an available resource for numerous species of arthro-
pods, including hemipterans associated with rice in
southern Brazil.
Pentatomoids (Hemiptera: Heteroptera) are widely
known for their number of species of agricultural interest
and several species have been found to be associated with
rice and grasses in general (Panizzi et al 2000). Study of these
insects in natural environments can contribute to decision
making regarding implementation of measures to control
pest species (Mendonça et al 2009). Pentatomoidea includes
around 5,720 nominal species, of which more than 600 are
found in Brazil (Grazia et al 1999).
Neotrop Entomol (2013) 42:240–245
DOI 10.1007/s13744-013-0116-6

This study sought to evaluate the role of tussocks of A.
bicornis in the composition, structure, and diversity of an
assemblage of pentatomoids at the edge of a rice culture.
More specifically, the study aimed to test the hypothesis
that A. bicornis may serve as a hibernation site for these
species by detecting seasonal diversity patterns.
Material and Methods
Study area
The study was carried out in the county of Eldorado do Sul,
Rio Grande do Sul (30°02′S, 51°23′W). It is a region with
extensive low-altitude (~10 m) plains (Rambo 1994) and a
humid subtropical climate, with an average annual temper-
ature of 19.5°C (Maluf 2000).
Owing to the climate, soil, and topography of the region,
the main agricultural activity in the region is irrigated rice
culture, alternating over time and space with cattle and
sheep breeding. In winters, native vegetation and stubble
grow in the fields. Throughout the year, many grass tus-
socks grow at the edges of the fields and roads.
Sampling
The sampling sites were four strips at the edges of irrigated
rice fields, which were selected since abundance of tus-
socks has been observed at the sides of secondary roads.
The width of these sites ranged from 4 to 20 m and the
length ranged from 30 to 50 m. From April 2010 to March
2011, on every fortnight, two tussocks of A. bicornis were
removed, each up to 30 m away from the crop and with a
distance of at least 4 m between the tussocks; removal was
alternated between the opposite edges of each strip.
Data analysis
Pentatomids and scutellerids were identified on the basis
of previous descriptions in the literature (Schouteden 1904,
Rolston & McDonald 1979,1981,1984, Rolston et al 1980)
and by comparisons with identified material from scientific
collections. Thyreocoridae specimens were identified by a
specialist (Viviana Cauduro Matesco, MSc, Universidade
Federal do Rio Grande do Sul, Porto Alegre, Brazil).
Voucher specimens were deposited in the collection at
the Museu de Ciências Naturais, Fundação Zoobotânica,
Porto Alegre, Brazil.
Sampling sufficiency curves for the number of species
obtained at each sampling time with 500 randomizations
were obtained by using Colwell’s EstimateS software
(2005). The observed species richness was estimated with
Bootstrap and Jackknife 1 by using the same software.
Species were classified as follows on the basis of abun-
dance (logarithmic scale): rare, log n≤1; intermediate, 1 <
log n≤2; and dominant, log n< 2. Correlations between
abundance and the variables tussock diameter and dis-
tance from the rice culture were analyzed by Spearman’s
correlation coefficient by using Bioestat 5.0 software
(Ayres et al 2007). Species diversity in each season was
estimated by the Berger–Parker (d), Margalef (D
Mg
),
Shannon–Wiener (H′), and Simpson’s complementary indi-
ces (1-D; Moreno 2001, Magurran 2004) by using Past 2.02
software (Hammer et al 2001). The adopted significance
level was 5% in all analyses.
Results and Discussion
In landscapes dominated by extensive irrigated rice cul-
tures, tussocks of A. bicornis are important shelters for
several pentatomoid species. Tussocks serve as refuges
for invertebrate fauna, including isopod crustaceans, spi-
ders, and several groups of insects (Pearce 1948, Luff 1965,
1966). This shelter function is directly related to the micro-
climate provided by the vegetation structure (Bossenbroek
et al 1977), which is more stable than the microclimates in
open environments.
We sampled 3,423 adult specimens of 22 species of
Pentatomoidea distributed in 13 genera belonging to three
families: Pentatomidae, Scutelleridae, and Thyreocoridae.
Pentatomidae showed the highest abundance and species
richness (3,358 specimens of 14 species), followed by
Thyreocoridae (59 specimens of seven species) and
Scutelleridae (six specimens of a single species; Table 1).
The highest abundance and species richness were
expected for Pentatomidae, since it is the largest family
in the group (Schmidt & Barcellos 2007). Currently, around
4,100 Pentatomidae species and 760 genera are recog-
nized (Schuh & Slater 1995, Grazia et al 1999, Grazia &
Schwertner 2008). Although Thyreocoridae had markedly
lower abundance, its speciesrichnesswasthesecond
highest. Galgupha Amyot & Serville had the highest num-
ber of species (seven) among all the pentatomoids. Species
of this genus are commonly found in the state of Rio
Grande do Sul (Mendonça et al 2009). Thyreocoridae was
the second most abundant and species-rich family in a
study in northwestern Rio Grande do Sul (Schmidt &
Barcellos 2007) as well. Taxonomic and biological informa-
tion about this family is still missing, but it is estimated that
about 220 species of this group have already been de-
scribed. These heteropterans are usually found in grasses,
invading plants and shrubs, where they feed and lay their
eggs mostly on flowers and developing fruits (McPherson
1971,1972, Biehler & McPherson 1982). In this study, the
following three species of Thyreocoridae were recorded for
Andropogon bicornis as a Hibernation Site for Pentatomoidea 241

the first time in Rio Grande do Sul: Alkindus crassicosta
Horvath, Galgupha longirostris Berg, and Galgupha porcata
Horvath.
Abundance and species richness were the lowest in
January, February, and March and the highest in July,
August, and September. With regard to different seasons,
abundance and species richness were the highest in winter,
followed by autumn, spring, and summer (Table 1).
Throughout the sampling period, no pentatomoid eggs or
nymphs were found in tussocks. No predatory pentatomids
(Asopinae) were found throughout our samplings.
Thomas et al (1992) found a higher density of predatory
beetles Tachyporus hypnorum Fabricius (Staphylinidae) and
Demetrias atricapillus L. (Carabidae) in tussocks than in the
adjacent vegetation with different growth structures.
Tussocks of the grasses Holcus lanatus,Festuca rubra,
and Poa trivialis, which have structures similar to that of
A. bicornis, showed a higher capacity for temperature
regulation than species in shrub or rosette form
(Bossenbroek et al 1977). At low temperatures, animals
sheltered in plants with dense structures have a higher
chance of survival than those in open environments, and
under these conditions, the protection provided by tus-
socks may be a major advantage for these species over
those in open environments (Bossenbroek et al 1977).
The use of tussocks by these species as protection
against extremes of temperature and humidity (Luff
1965,Bossenbroeket al 1977) was not verified during
summer, when the abundance and species richness in
this shelter were practically null. Rather, the highest
diversity of pentatomoid bugs was recorded during the
colder months. These results corroborate the hypothe-
sis that tussocks of A. bicornis serve as hibernation
sites for several species, as in the case of beetles that
take shelter in tussocks of Dactylis glomerata (Luff
1966). In fact, imaginal diapause has been observed
in Tibraca limbativentris Stål (Klein et al 2012).
The absence of immature specimens throughout the year
suggests that A. bicornis is not a host plant for pentatomoids
in the region according to the criteria established by
Schoonhofen et al (2005). These authors defined a host as
a plant that allows feeding and reproduction of individuals of
Table 1 Pentatomoidea
(Hemiptera) species recorded
in tussocks of Andropogon
bicornis in Eldorado do Sul, RS,
Brazil, by season
(rf relative frequency).
Taxa Autumn Winter Spring Summer fr (%)
Pentatomidae
Acledra kinbergi (Stål) 1 0.02
Chinavia musiva (Berg) 1 0.02
Chinavia nigridorsata (Breddin) 4 3 0.20
Dichelops australis Klein & Grazia 1 0.02
Dichelops furcatus (Fabricius) 7 3 0.30
Edessa meditabunda (Fabricius) 135 274 2 12.0
Edessa rufomarginata (De Geer) 1 0.02
Glyphepomis adroguensis Berg 4 0.13
Hypatropis inermis (Stål) 7 42 1.43
Oebalus poecilus (Dallas) 3 7 1 0.33
Oebalus ypsilongriseus (De Geer) 239 323 88 19.0
Poriptus luctans Stål 5 1 0.17
Thoreyella cornuta Berg 1 0.02
Tibraca limbativentris Stål 417 1509 276 3 64.4
Scutelleridae
Orsilochides leucoptera (Germar) 3 3 0.18
Thyreocoridae
Alkindus crassicosta Horvath 3 0.08
Galgupha fossata McAtee & Malloch 2 0.05
Galgupha longirostris Berg 5 0.15
Galgupha neobisignata McAtee & Malloch 3 13 0.46
Galgupha oblonga McAtee & Malloch 4 27 0.90
Galgupha porcata Horvath 1 0.02
Galgupha sp. 1 0.02
Abundance 832 2187 395 9 100
Species richness 14 15 6 3
242 Klein et al

a single species. Studies performed to identify host plants for
pentatomoids in the central region of Rio Grande do Sul
(Lopes et al 1974,Garletet al 2010) have not mentioned
collection of immature specimens or described any feeding
activity; therefore, the association between the insect and
the host plant remains unclear.
Bunde et al (2010) considered a host to be the
vegetation in which adults or nymphs could feed on or
in a state of diapause; this criterion differs from the
concept described by Schoonhofen et al (2005), which
was the used in this study. Nevertheless, records of the
plant species from which insects were collected are
relevant. Twenty-six species of grasses were listed as
being associated with pentatomids in Rio Grande do Sul
(Link & Grazia 1987).
The species accumulation curve (Fig 1) showed a ten-
dency towards asymptote, which suggests that the number
of sampled species is close to the estimated species rich-
ness. Species richness estimated using Bootstrap and
Jackknife 1 indicated that 87.4% and 74.1% of the species,
respectively, were sampled.
The assemblage structure of Pentatomoidea had three
dominant, five intermediate, and 14 rare species, of which
36.4% corresponded to singletons and doubletons (Fig 2).
The three dominant species in decreasing order of abun-
dance were T. limbativentris,Oebalus ypsilongriseus
(De Geer), and Edessa meditabunda (Fabricius). The first
species was present in all seasons, and no individual belong-
ing to the other two species was found among the popula-
tion sampled in summer.
The two most abundant species (T. limbativentris and O.
ypsilongriseus) use rice as a host (Panizzi et al 2000). In
particular, T. limbativentris is considered a rice culture
pest. Most of the recorded species in the related literature,
however, are not known to use rice as the host plant,
which suggests that A. bicornis serves as a hibernation site
for different species of pentatomoids.
The highest species richness was observed in winter and
was demonstrated by the highest Margalef index value in
that season (D
Mg
=1.949). On the other hand, indices based
on the proportional abundance of species, such as
Shannon–Wiener and Simpson’s complementary indices
(Magurran 2004), showed higher values for autumn, there-
by indicating lower dominance by T. limbativentris (H′=
1.236) and (1-D=0.6375), respectively. The Berger–Parker
index, which expresses the proportional abundance of the
most abundant species, indicated spring to be the season
with the highest species diversity (d= 0.6987).
At three Atlantic Rainforest fragments in the state of
Santa Catarina, the lowest values of abundance and species
richness were recorded in winter, whereas the highest
corresponding values were recorded in December, March,
and April (Campos et al 2009). In savanna–steppe type
vegetation in southeastern Rio Grande do Sul, the highest
abundance was recorded in autumn and summer (Bunde et
al 2010). The difference between the patterns found in this
study and those recorded by other authors can be attrib-
uted to the differences in the sampling methods used,
which included beating and/or sweeping, as well as differ-
ences in environment types.
There was a significant correlation between tussock
diameter and abundance of specimens in autumn (r
s
=
0.346, P=0.0158), winter (r
s
=0.358, P=0.0066), and spring
(r
s
=0.308, P=0.0329). This is a reasonable finding since
bigger tussocks would allow a larger number of stinkbugs
to take shelter, thus decreasing the competition for space.
The stability of the populations that use these tussocks
depends, among other factors, on their size (Pearce 1948).
With regard to the distance from the rice culture, we
initially assumed that tussocks that were closer would
show greater abundance of species associated with rice;
however, this did not prove significant within the scale
studied. This finding can be attributed to the flight ability
and dispersion of these stink bugs. In the laboratory,
Fig 1 Species accumulation curve and estimated species richness of
pentatomoids sampled in tussocks of Andropogon bicornis from April
2010 to March 2011 in Eldorado do Sul, Rio Grande do Sul, Brazil.
Fig 2 Distribution of Pentatomoidea species abundance recorded
from April 2010 to March 2011 in tussocks of Andropogon bicornis
collected in Eldorado do Sul, Rio Grande do Sul, Brazil.
Andropogon bicornis as a Hibernation Site for Pentatomoidea 243

specimens of different populations of diapause-induced
Nezara viridula (L.) flew more intensely than those that
did not receive the stimulus (Gu & Walter 1989). In the
field, we observed that individuals that would later hiber-
nate flew longer distances than those that kept feeding
and showed no evidence of diapause.
At large scale, presence of tussocks adds heterogeneity
to the landscape, affecting the diversity of invertebrates
(Helden et al 2010). Andropogon bicornis is widely distrib-
uted on the edges of cultivated fields and on roadsides in
the region. In a mainly rice-growing region, with only a few
remnants of alluvial woods, these tussocks play an impor-
tant role as refuges for various species in adverse condi-
tions. The high species richness observed in the colder
months, resulting from the presence of species related to
rice as well as unrelated species, combined with the ab-
sence of immature specimens in the tussocks supports our
hypothesis that A. bicornis may serve as a hibernation site
for pentatomoids.
Acknowledgments The authors would like to thank Viviana Cauduro
Matesco, MSc for Thyreocoridae identification and CNPq and CAPES
for fellowships to two of the authors.
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