Download Impact of prescribed burning on endophytic insect

Biodiversity and Conservation 13: 1875–1888, 2004.
# 2004 Kluwer Academic Publishers. Printed in the Netherlands.
Impact of prescribed burning on endophytic insect
communities of prairie perennials (Asteraceae:
Silphium spp.)
JOHN F. TOOKER and LAWRENCE M. HANKS*
Department of Entomology, University of Illinois at Urbana-Champaign, 320 Morrill Hall, 505 South
Goodwin Avenue, Urbana, IL 61801, USA; *Author for correspondence (e-mail: [email protected];
fax: +1-217-244-3499)
Received 4 February 2003; accepted in revised form 4 July 2003
Key words: Antistrophus, Biodiversity, Conservation, Cynipidae, Endemic species, Eurytomidae, Fire,
Mordellidae, Population dynamics
Abstract. Prescribed burning currently is used to preserve endemicity of plant communities in remnant
tallgrass prairies. Although some types of arthropods benefit from changes in plant communities brought
about by burning, other species that are endemic to prairies may be threatened. Because they inhabit the
‘fuel layer’ of prairies, endophytic insects would seem particularly susceptible to this management tactic.
In this paper, we assess the impact of prescribed burning on endophytic insect communities inhabiting
stems of Silphium laciniatum L. and S. terebinthinaceum Jacquin (Asteraceae), endemic prairie plants.
Populations of these insects were decimated by burning, with mortality approaching 100% in most cases.
Their populations nevertheless began to rebound within a single growing season, with densities moderately but significantly reduced 1 year after the burn. Even when a prairie remnant was completely
incinerated, plant stems were recolonized by insects within one growing season. Our findings suggest
that sufficient numbers of endophytic insects survive burns in remains of Silphium to recolonize burned
areas the following year.
Abbreviations: S. lac. – S. laciniatum; S. ter. – S. terebinthinaceum; RBP – Red Bison Prairie; TP –
Trelease Prairie; LCP – Loda Cemetery Prairie Nature Preserve; PCP – Prospect Cemetery Prairie Nature
Preserve; WCP – Weston Cemetery Prairie Nature Preserve.
Introduction
Loss of natural ecosystems to urban sprawl and expansion of agriculture has intensified the need for conservation of insect species worldwide (Samways 1994).
Among North American ecosystems, the tallgrass prairie of the Midwest is among
the most imperiled, diminished to only *4% of its pre-settlement area (Samson
and Knopf 1994; Steinauer and Collins 1996). Tallgrass prairie survives today as
isolated remnants and restorations (Samson and Knopf 1994). These prairie fragments commonly are managed by periodic prescribed burning that eliminates
exotic weeds, preserves endemicity of plant communities, and plays an important
role in nutrient cycling (Steinauer and Collins 1996; Pauly 1997). Prescribed burns
typically consume most of the herb layer of prairies, charring or completely incinerating dead stems of grasses and forbs (Pauly 1997), and can threaten insect
communities (see Swengel 2001a for review).
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To conserve insect communities, land managers commonly subject only a portion of a prairie to burning in any one year (Taron 1997), hence referred to as
‘restricted burning’. Nevertheless, this strategy often results in declines in abundance of insect species that are endemic to prairie habitats, while habitat generalists, whose populations extend beyond prairie boundaries, can recolonize from
adjacent habitats (Panzer 2002). Among prairie endemics, vagile species and soil
dwellers that can escape the flames may be favored by changes in the plant community brought about by burning (Swengel 2001a; Meyer et al. 2002). On the other
hand, less vagile species that inhabit the ‘fuel layer’ of the plant community are
highly vulnerable to burning and suffer dramatic reductions in species diversity and
abundance (Fay and Samenus 1993; Swengel 2001a).
In this article, we evaluate the impact of prescribed burning on endophytic insect
communities that live within stems of two species of Silphium (Asteraceae). Endophytic insects are rarely considered in assessing the impact of burning (see
Swengel 2001a), but they appear to be particularly abundant in prairies (Williams
1999) and especially vulnerable to local extirpation because of their narrow host
ranges, the endemicity of their host plants, and their inhabiting the fuel layer of
prairies (Rice 1932; Fay and Samenus 1993). We previously have characterized this
endophytic community (Tooker and Hanks 2004), avoiding taxonomic limitations
that can compromise evaluation of the impact of burning (see Arenz and Joern 1996;
Panzer 2002). Moreover, our study species are primarily hymenopterans, a group that
has been neglected in earlier burn studies (e.g., see Swengel 2001a; Panzer 2002). At
prairies routinely managed with fire, we evaluated the impact of prescribed burning
on the herbivorous species and their dominant parasitoids, and the entire endophytic
community, by conducting four studies that assessed: (1) survival of a restricted burn;
(2) recovery of populations following a restricted burn; (3) dispersal and recolonization of burned areas; and (4) recovery of populations after a complete burn.
Materials and methods
Study system
The host plants Silphium laciniatum L. and S. terebinthinaceum Jacquin are sibling
species and among the most conspicuous herbaceous perennials of tallgrass prairies
of the midwestern United States (Gleason and Cronquist 1991; Clevinger and Panero 2000). Both species produce as many as 12 flowering stems per plant that
reach heights of 2–4.5 m (Weaver 1954). In central Illinois, where we conducted
our studies, S. laciniatum bolts in mid- to late May and S. terebinthinaceum in midto late June (Tooker and Hanks 2004). Flowering stems senesce and die before
winter, detaching from the taproot and usually falling to the ground, but often are
supported in an upright position by surrounding vegetation (Tooker and Hanks
2004). S. laciniatum and some congeners have been listed as threatened or endangered in some parts of the Midwest (Roberts and Cooperrider 1982; Ladd 1997;
Walter and Gillett 1998).
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Stems of S. laciniatum and S. terebinthinaceum harbor a diverse community of at
least 13 species of Hymenoptera and one species of Coleoptera (see Tooker and
Hanks (2004) for community composition and biology). The dominant species are
the gall wasps Antistrophus rufus Gillette and A. minor Gillette (Hymenoptera:
Cynipidae) and their hymenopteran parasitoids (comprising *95% of the total
number of insects). A. rufus and A. minor feed within ellipsoid galls formed in the
pith and cambium of stems, and their galls are not discernable externally (Gillette
1891; Beutenmüller 1910; Tooker et al. 2002; Tooker and Hanks 2004). Adults of
both sexes have fully developed and functional wings, but nevertheless do not fly
readily, usually walking or taking occasional hopping flights to nearby plants
(Tooker and Hanks 2004). A. rufus appears to comprise at least two cryptic species,
one associated with S. laciniatum and the other with S. terebinthinaceum (Tooker
et al. 2002). These Antistrophus species are attacked by a suite of at least eight
hymenopteran parasitoids, but Eurytoma lutea Bugbee accounts for *85% of
parasitism (Tooker and Hanks 2004).
Stems of S. laciniatum and S. terebinthinaceum also are inhabited by larvae of
the beetle Mordellistena aethiops Smith (Mordellidae) that feed primarily on pith
tissue, but occasionally consume inhabitants of Antistrophus galls (Tooker and
Hanks 2004). M. aethiops, in turn, is attacked by three species of parasitoids with
the braconid Schizopyrmnus sp. accounting for *81% of parasitism (Tooker and
Hanks 2004).
Endophytic insects are concentrated in the bases of S. laciniatum stems, but are
more evenly distributed in stems of S. terebinthinaceum (Tooker and Hanks 2004).
This difference between the species in within-stem dispersion of insects may have
important implications for the impact of burning because apices of Silphium stems
often survive burns and therefore may provide a partial refuge from fire in S.
terebinthinaceum (Tooker and Hanks 2004).
Study sites
Our study sites were mesic, black soil, tallgrass prairies dominated by Andropogon gerardii Vitman, Schizachyrium scoparium (Michaux) Nash, and Sorghastrum
nutans (L.) Nash, and had at least 30 mature plants of S. laciniatum and/or S.
terebinthinaceum. Each prairie was a well-defined habitat island with sharp ecological boundaries and most were surrounded by agricultural fields. Study sites
included three prairie remnants and two restorations in four counties of central
Illinois (Figure 1; see Tooker and Hanks 2004): Red Bison Prairie Corridor (RBP;
Champaign Co., 1.7 ha restoration, a *11 m wide by 1.6 km long railroad rightof-way owned by Canadian National Railroad; 40804.810 N, 88814.830 W), Trelease Prairie (TP; 7.3 ha restoration, Champaign Co., University of Illinois Natural
Area; 40807.760 N, 88808.590 W), Loda Cemetery Prairie Nature Preserve (LCP;
Iroquois Co.; 1.4 ha remnant; The Nature Conservancy; 40831.610 N, 88804.570
W), Prospect Cemetery Prairie Nature Preserve (PCP; Ford Co.; 2 ha remnant;
Paxton Township Cemetery Association; 40826.710 N, 88805.870 W), and Weston
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Figure 1. Location of study sites in east central Illinois: (1) Red Bison Prairie Corridor, (2) Trelease
Prairie, (3) Loda Cemetery Prairie Nature Preserve, (4) Prospect Cemetery Prairie Nature Preserve, (5)
Weston Cemetery Prairie Nature Preserve.
Cemetery Prairie Nature Preserve (WCP; McLean Co.; 2 ha remnant; Yates
Township and Parklands Foundation; 40844.790 N, 88836.800 W). Four of these
sites (RBP, TP, PCP, WCP) have been regularly managed with fire in the recent
past with one-quarter to one-half of their area burned at least every other year,
whereas one (LCP) had not been burned for at least 5 years prior to 2001. LCP,
PCP, and WCP are part of the Illinois Nature Preserves System (McFall and
Karnes 1995).
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Impact of burning on endophytic insect communities
We studied the impact of burning on endophytic insect communities of S. laciniatum and S. terebinthinaceum by collecting stems just before the prairie was
burned, often on the same day as the burn, and remains of stems within a few days
after the burn. We arbitrarily collected stems from different plants at each site,
limiting pre-burn samples to 10–40 stems per year, depending on plant abundance,
to minimize our impact on insect communities. After burns, we collected remains
of 5–30 Silphium stems per site. Although only the remains of burned stems were
collected, insects emerging from them nevertheless represented the total number of
survivors of the entire stem. We sectioned stems to fit within individual food
storage bags (3.8 L volume), and stored these bags in an unheated outbuilding in
Urbana, Illinois, until all adult insects had emerged. We counted insects in bags to
determine the total number per species that emerged per stem. We evaluated the
impact of burning on the most abundant herbivores and their dominant parasitoids,
including Antistrophus species, E. lutea, M. aethiops, and Schizopyrmnus sp., as
well as the entire complex of insects that emerged from stems.
The great numbers of zeros in our data sets violated assumptions of analysis of
variance (Sokal and Rohlf 1995), necessitating nonparametric statistics to test
differences between means (PROC NPAR1WAY, SAS Institute 2001): we used the
Wilcoxon rank sum test to compare densities of insects per stem from burned and
unburned areas sampled within the same year, and the Kruskal–Wallis test to
compare changes in density over time (before and after burns). Differences between
individual means were tested with the LSD means separation test (Sokal and Rohlf
1995). We report means 1 SE throughout unless stated otherwise.
Survival of a restricted burn
To evaluate survival of endophytic insect communities after a restricted burn, we
collected stems at four prairies in two different years. Prairie study sites were
managed differently from one another, necessitating different sampling methods.
PCP was managed by burning one-half of the prairie every other year. Neither side
was burned in 1999 and we collected stems of S. terebinthinaceum from northern and
southern halves during winter 1999–2000 to estimate pre-burn densities. The
northern half was burned in late March 2000 and we recovered remnants of stems
from the burned area on 1 April 2000. We also collected stems from the southern half
just before it was burned on 9 April 2002 and remains of stems the day after.
TP was managed by burning about one-quarter to one-half of its area every year.
We collected stems of S. terebinthinaceum before and after burns of the northwest
and southeast quadrants in late fall 1999 and spring 2000, respectively, combining
pre- and post-burn samples from both quadrants.
The long and narrow RBP site was managed by burning different portions on an
annual basis. We collected stems of S. terebinthinaceum from a *100 m section
just before and after it was burned on 30 October 1999.
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WCP was managed by burning half of the site each year. We collected stems of
S. laciniatum before and after burns of the west half on both 15 April 2000 and 15
April 2002.
Recovery of populations following a restricted burn
To evaluate recovery of insect populations after a burn, we collected stems of S.
terebinthinaceum from northern and southern halves of PCP in spring 2001, 1 and 3
years after northern and southern halves had been burned, respectively (see above).
We predicted that insect densities would be lower in the northern half due to its
being burned more recently.
Dispersal and recolonization of burned areas
We studied the spatial pattern of recolonization after WCP was burned on 15 April
2000. We hypothesized that insects would colonize the burned portion of the prairie
from the unburned portion during the 2000 growing season. Given the sedentary nature
of the gall wasps, we predicted that plants in the burn zone that were closest to the burn
boundary would be colonized by a greater number of insects than those at greater
distances. To test this hypothesis, we collected stems of the 2000 growing season from
within the burn zone and at varying distance from the boundary. Stems were collected
on 5 April 2001. Stems of S. laciniatum were located 4, 7, 10, 24, and 43 m from the
boundary, and stems of S. terebinthinaceum were 11, 17, 20, and 28 m from the
boundary (n = 3 stems per distance; distance determined by natural distribution of
plants). We tested the relationship between insect density per stem and distance from
the burn boundary by linear regression (PROC REG, SAS Institute 2001).
Recovery of populations after a complete burn
In spring 2001, arson provided us the unfortunate opportunity to study recovery of
insect populations after a burn that consumed an entire prairie. LCP usually had been
managed by burning half of the site on an approximately annual basis, but had not been
burned for about 5 years when it was set ablaze on 31 March 2001 and completely
burned (personal observation). We had collected stems of S. laciniatum and S. terebinthinaceum from the site in winter 1999–2000 (two winters before the burn), winter
2000–2001 (preceding the burn), and winter 2001–2002 (one season after the burn).
Results
As in our previous studies (Tooker and Hanks 2004), Antistrophus gall wasps and
their hymenopteran parasitoid E. lutea were by far the most abundant endophytic
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species (Tables 1–3). The mordellid M. aethiops and its parasitoid Schizopyrmnus
sp. usually were too rare to provide robust statistical tests of the impact of burning
on insect abundance.
Survival of a restricted burn
Burning had a severe impact on survival of insects at most sites, with few if any
insects emerging from remains of stems recovered after burns (‘All species’ in
Table 1). Exceptions were PCP and WCP in 2002, where substantial proportions of
gall wasps and E. lutea survived. On average, remains of burned stems yielded only
6.4 3.8% of the number of insects that emerged from stems collected before burns
(mean for ‘All species’). These findings suggest that insect larvae had been killed
by heat even in portions of stem that were not consumed by fire. All of the insect
species showed the same vulnerability to burning in both plant species (Table 1).
Recovery of populations following a restricted burn
One year after the restricted burn at PCP in 2000, we reared from stems of S.
terebinthinaceum 26.7% fewer insects from stems collected in the area that was
burned the previous year than from stems collected from the area that had not been
burned for 3 years (Table 2; ‘All species’). These findings suggest that the burn had
a lingering, but moderate impact on population densities.
Dispersal and recolonization of burned areas
In the area of WCP that had been burned the previous year, densities of insects in
stems averaged 184 26 and 90.8 15 insects per stem for S. laciniatum and S.
terebinthinaceum, respectively, but density was not correlated with distance of
stems from the burn boundary (S. laciniatum: r2 = 0.006, P > 0.05; S. terebinthinaceum: r2 = 0.013, P > 0.05). The lack of a distance effect suggests that
colonization of plants bolting in the burned area was not influenced by the distance
of plants from the unburned area, the presumed source of female insects.
Recovery of populations after a complete burn
During a 3-year period at LCP, average densities of insects per Silphium stem in
winter varied more dramatically in S. laciniatum than in S. terebinthinaceum (Table
3). Both species showed significant differences between years in insect density (‘All
species’), with post-burn reductions of 65% in S. laciniatum and 16% in S. terebinthinaceum; however, the LSD test did not identify significant differences between individual means for S. terebinthinaceum despite the highly significant
Insect species
All species
Antistrophus spp.
E. lutea
M. aethiops
Schizopyrmnus sp.
All species
Antistrophus spp.
E. lutea
M. aethiops
Schizopyrmnus sp.
All species
Antistrophus spp.
E. lutea
M. aethiops
Schizopyrmnus sp.
All species
Antistrophus spp.
E. lutea
M. aethiops
Schizopyrmnus sp.
Site, year, plant species
PCP 2000 S. ter.
PCP 2002 S. ter.
TP 2000 S. ter.
RBP 1999 S. ter.
After burn
0 (N = 5)
0
0
0
0
2.50 1.3 (N = 17)
1.17 0.96
0.22 0.17
0
0
0 (N = 32)
0
0
0
0
1.38 0.90 (N = 25)
1.19 0.88
0.19 0.19
0
0
Before burn
40.4 13 (N = 10)
29.1 12
4.20 1.8
0.30 0.21
0.10 0.1
9.65 2.8 (N = 23)
4.35 2.4
2.39 0.73
0.35 0.12
0.43 0.15
103 18 (N = 18)
25.2 4.5
64.5 13
0.55 0.14
1.10 0.26
72.9 13 (N = 15)
38.9 9.2
23.9 4.5
1.20 0.35
0.80 0.25
No. of insects per stem (N = no. of stems)
1.9
3.0
0.8
0
0
0
0
0
0
0
20.6
21.2
8.4
0
0
0
0
0
0
0
Estimated % survival
505****
499****
458****
432****
419****
890****
890****
890****
720****
754****
252***
276**
304*
315**
325*
15.0**
17.5**
22.5*
35.0
37.5
Wilcoxon statistic
Table 1. Number of insects (mean 1 SE) reared from flowering stems of S. laciniatum (‘S. lac.’) and S. terebinthinaceum (‘S. ter.’) before burns (entire stem
sampled) and after restricted burns (remains of stem sampled). ‘All species’ included the herbivores and parasitoids listed, as well as other species that emerged from
stems. ‘Year’ denotes the timing of the burn. ‘Estimated % survival’ is calculated by dividing post-burn densities by pre-burn densities. P values for Wilcoxon statistics
are indicated by *P < 0.05, **P < 0.01, ***P < 0.001, and ****P < 0.0001.
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Insect species
All species
Antistrophus spp.
E. lutea
M. aethiops
Schizopyrmnus sp.
All species
Antistrophus spp.
E. lutea
M. aethiops
Schizopyrmnus sp.
Site, year, plant species
WCP 2000 S. lac.
WCP 2002 S. lac.
Table 1. (continued)
After burn
0 (N = 26)
0
0
0
0
34.1 20 (N=16)
28.7 18
3.19 2.9
0
0.06 0.06
Before burn
120 26 (N = 13)
77.0 17
29.9 7.0
0.31 0.17
0.23 0.12
182 24 (N = 30)
140 21
30.8 4.1
0.33 0.13
0.13 0.08
No. of insects per stem (N = no. of stems)
15.8
17.0
9.4
0
31.6
0
0
0
0
0
Estimated % survival
176****
176****
179****
320*
367
442****
442****
442****
307**
307**
Wilcoxon statistic
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Table 2. Number of insects (mean 1 SE) emerging from flowering stems of S.
terebinthinaceum collected in spring 2001 from an area of PCP that had not been
burned for 3 years (‘Unburned area’) and an area that was burned the previous
spring (‘Burned area’). ‘All species’ included the herbivores and parasitoids listed,
as well as other species that emerged from stems. Schizopyrmnus sp. was absent
from all samples. Symbols for P values as in Table 1.
Insect species
All species
Antistrophus spp.
E. lutea
M. aethiops
Number of insects per stem
Unburned area
(N = 11 stems)
Burned area
(N = 10 stems)
75.9 3.7
58.8 3.3
8.0 1.5
0.36 0.15
55.6 4.9
36.9 2.8
13.4 1.4
0.44 0.18
Wilcoxon statistic
50.0**
54.0**
116
98.5
Kruskal–Wallis statistic (Table 3). Insect density in S. laciniatum did not vary
significantly between winters following the burn and 2 years earlier. Thus, it is not
clear whether moderately lower arthropod densities in winter 2002 were due to
burning or natural variation in population density. These data nevertheless clearly
demonstrate that populations of endophytic insects were not eradicated by this
complete burn and reestablished during the growing season following the complete
burn of the prairie, but at significantly lower densities.
Discussion
Our studies reveal that few endophytic insects survived prescribed burns, even in
unburned remains of stems (Table 1), a finding consistent with earlier studies (Fay
and Samenus 1993; Swengel 2001a). Survival was similarly low in S. laciniatum
and S. terebinthinaceum despite the fact that a greater proportion of insects are
present in apices of S. terebinthinaceum stems (Tooker and Hanks 2004). Nevertheless, substantial numbers of gall wasps and parasitoids survived burns at some
sites in some years (Table 1), suggesting that burning has an inconsistent impact,
perhaps due to the speed and/or temperature of the fire, which can be influenced by
humidity, fuel load, plant community composition, topography within sites, and
other environmental factors (Pauly 1997).
Although prescribed burning usually decimated populations of endophytic insects inhabiting the ‘fuel layer’ of prairies, our studies further revealed that insect
communities persisted. For example, few if any insects survived in the portion of
PCP that was burned in 2000 (Table 1, ‘After burn’), and densities rebounded by
spring 2001, although to levels that were significantly lower than in the area that
had not been burned (Table 2). The fact that densities in 2001 were lower in the area
that had been burned in 2000 than in the area that had not been burned for 3 years
(Table 2) suggests that burning does have a lingering, although subtle impact on
insect density. Persistence in spite of burning also was evidenced by recolonization
All species
Antistrophus spp.
E. lutea
M. aethiops
Schizopyrmnus sp.
Insect species
Winter
before burn
(N = 38)
233 20b
111 11b
86.2 8.3b
0.29 0.08
0.61 0.17
Two winters
before burn
(N = 27)
69.5 12a
46.3 9.2a
20.3 3.7a
0.48 0.2
0.63 0.17
S. laciniatum
Number of insects per stem
82.3 18a
64.9 14a
8.8 2.7a
0.31 0.20
0.63 0.20
Winter
after burn
(N = 16)
39.1****
21.3****
46.2****
1.07
0.32
K-W
statistic
32.1 8.7a
25.9 8.1a
4.3 1.4a
0.88 0.27
0
Two winters
before burn
(N = 16)
58.4 6.6a
22.3 3.4a
17.5 2.9b
0.33 0.08
0.33 0.11
Winter
before burn
(N = 39)
S. terebinthinaceum
49.0 36a
36.6 32a
9.0 4.4a
0.33 0.14
0.42 0.23
Winter
after burn
(N = 12)
14.9***
8.23*
10.6**
3.35
4.94
K-W
statistic
Table 3. Number of insects (mean 1 SE) reared from flowering stems of S. laciniatum and S. terebinthinaceum before and after a complete burn of LCP that
occurred on 31 March 2001. ‘All species’ included the herbivores and parasitoids listed, as well as other species that emerged from stems. Significant differences
between means within the same row are indicated by different letters (LSD test). Symbols for P values as in Table 1.
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of LCP during the growing season following a burn that consumed the entire
prairie. Burned areas of these prairies may have been re-colonized by immigrants
from nearby prairie habitats, which at LCP could have been a railroad right-of-way
about 400 m to the east. Such source populations are not available for most prairie
sites in central Illinois, however, because they are engulfed by agroecosystems
(ILENR 1994). An ability to disperse over short distances also was indicated by the
absence of a distance effect in recolonization of the burned area at WCP. Because
A. rufus does not take flight readily, however, immigration may be infrequent and
recolonization of isolated prairie remnants may depend on survival of insects within
the site. Relatively small numbers of adult female A. rufus may be necessary to
recolonize a burned prairie because of their high fecundity compared to other
species in the system (egg load averages 160 11 eggs per female, unpublished
data).
We conclude from these studies that the endophytic insect communities associated with S. laciniatum and S. terebinthinaceum are resilient and endure despite
destruction of their habitat by fire, as can other insect species that are confined to
prairie remnants (Panzer 2002). Our research findings therefore support judicious
use of prescribed burning. Because we did not compare our managed prairie sites
with unmanaged prairies, however, there remains the possibility that the community of insects we studied has lower species diversity and/or is chronically
suppressed by periodic burning compared to sites that are never burned. Moreover, we caution that the possibility remains that other insect species, including
those associated with rare plant species, or those that are patchily distributed
within prairie remnants, may be subject to local extirpation by this management
practice (Orwig and Schlicht 1999; Swengel 2001a). This risk is particularly
acute because so little is known of prairie insect communities (Kosztarab and
Schaefer 1990; Arenz and Joern 1996), especially endophytic insects (Williams
1999), and negative influences of burning on insect communities appear relatively
common (e.g., Fay and Samenus 1993; Orwig and Schlicht 1999; Swengel
2001a, b).
Acknowledgements
We appreciate assistance provided by M.W. Tooker, J.A. Mohler, and A.L. Crumrin
in the field and lab. We also thank S. Buck, J. Taft, M.K. Solecki, R.C. Anderson,
and members of Red Bison (a University of Illinois Registered Student Organization) for conducting burns at these sites. Thanks also to the Illinois Nature
Preserves Commission, Red Bison, and the Committee of Natural Areas of the
School of Integrative Biology, University of Illinois at Urbana-Champaign (UIUC),
for permitting access to our study sites. This work was in partial fulfillment of a
Ph.D. degree for J.F.T. from UIUC. Funding was provided in part by a Sigma Xi
Grant-in-Aid of Research, a grant from Prairie Biotic Research, Inc., and a Summer
Research Grant from the Program in Ecology and Evolutionary Biology in the
School of Integrative Biology, UIUC.
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