Bruner Slantfaced Grasshopper
Bruneria brunnea (Thomas)
Link directly to photos of adults, nymphs,
Distribution and Habitat
B. brunneacontinental distribution map
Wyoming distribution map
The Bruner slantfaced grasshopper (also known as Stenobothrus brunneus)
ranges widely in the hills and mountains of the northwestern United States.
It lives in the mixedgrass and bunchgrass prairies, in mountain meadows
and parklands, and in alpine tundra. In the northern mixedgrass prairie
its distribution extends into eastern North Dakota and southwestern Manitoba,
where populations are small and local on suitable hillsides. Altitudes
of its known habitats range from 1,600 to 11,100 feet.
When populations of the Bruner slantfaced grasshopper irrupt, the species
becomes a serious pest of mountain and foothill grasslands. In 1920 its
depradations were observed on rangelands of southwestern British Columbia.
A dense infestation covering 2,000 square miles caused considerable damage
to range grasses. The Bruner slantfaced grasshopper made up 50 percent
of the assemblage, Camnula pellucida 30 percent, and Melanoplus
sanguinipes and several other species 20 percent. In the mountains
and foothills of Wyoming from 1988 to 1994, populations of the Bruner slantfaced
grasshopper ranged from less than 0.1 to 15 per square yard. In the latter
case, density of the assemblage was estimated to be 25 grasshoppers per
square yard. The rest of the infestation was comprised of four other grass
feeders and one forb feeder in approximately equal numbers.
As a subdominant species, the Bruner slantfaced grasshopper may add
to the damage of a dominant species. In 1989, a grassland site in the Big
Horn Mountains of Wyoming was infested by an assemblage of 20 adult grasshoppers
per square yard. This assemblage consisted of three grass feeders: Camnula
pellucida, 40 percent; the Bruner slantfaced grasshopper, 10 percent;
Chorthippus curtipennis, 10 percent;
and three forb feeders: Melanoplus bruneri, 23 percent; M.
borealis, 13 percent; and M. alpinus, 4 percent. During the
period 1988-94, densities of most populations of the Bruner slantfaced
grasshopper recorded in the annual grasshopper survey of Wyoming grasslands
were low and economically insignificant; 118 of 148 (80 percent) sites
surveyed contained less than one grasshopper per square yard. Although
no experimental study of damage to forage has been made, estimates may
be made from the weights of adults. Live weights of males collected from
a mountain meadow in the Laramie Range averaged 223 mg and females 376
mg (dry weights: males 46 mg, females 96 mg).
The Bruner slantfaced grasshopper feeds on grasses and sedges. The precise
diet depends on plants available in its widespread habitats. Observations
in Canada indicate that in the northern mixedgrass prairie it feeds on
species of Agropyron, Bouteloua, Carex, Koeleria,
and Stipa. In Wyoming, examination of crop contents of Bruner slantfaced
grasshoppers collected from two mountain meadows, one in the southern Laramie
Range and the other in the northern Big Horn Mountains, revealed that the
grasshoppers had fed on mountain grasses and sedges (Table
1). The results suggest that certain grasses and sedges are selected
as host plants including Idaho fescue, spikefescue, thickspike wheatgrass
(Elymus lanceolatus), needleandthread, rock sedge, and threadleaf
sedge. Differences in diet of the grasshoppers living in the two meadows
appeared to be due to the presence and abundance of individual plant species
in the habitat. For example, Idaho fescue was scarce in the Pole Mountain
meadow but abundant in the Big Horn Mountain meadow; rock sedge was absent
in the Pole Mountain meadow but common in the Big Horn Mountain meadow.
Two-choice cage tests showed that the Bruner slantfaced grasshopper exhibits
selectivity in feeding on grasses, confirming that certain grass species
in the natural habitat are preferred to others. One field observation of
feeding revealed its method of attacking host plants. In a meadow of the
Big Horn Mountains, an adult male was discovered walking at 10:55 a.m.
DST on 4 August 1994. The temperature of soil surface was 81°F and
of air at the 1-inch level 64°F, and the sky was clear. It came to
a rock sedge, raised up diagonally on the plant, and cut a leaf 1/2 inch
above the base. Resting horizontally on the ground surface, the grasshopper
consumed the detached section, about 2 inches long, from the cut end to
the tip. Adults caged on transplanted sod from a mountain meadow habitat
fed in much the same way on grass. For example, a female raised up diagonally
on a grass plant, cut a green leaf 1/2 inch above the base, held onto the
cut section with the front tarsi, and consumed the whole 2-inch cut section.
It attacked another leaf in the same manner. A male was observed to move
onto a grass plant, cut a green leaf of 5 inches length at the 2-inch level,
hold onto the cut section with the front tarsi, and feed on the leaf. This
male also turned head-down on the plant and cut another green leaf, held
onto the cut section with the front tarsi, and consumed the entire cut
section. Caged grasshoppers were also observed to feed in short bouts on
Dispersal and Migration
Flushed flight of the Bruner slantfaced grasshopper is straight and silent.
The adults travel a distance of 2 to 8 feet at heights of 4 to 6 inches.
They usually land on the ground headed away from the intruder.
Evidence for migration is meager. One long-winged female was discovered
frozen along with specimens of known migratory species on a glacier in
the Crazy Mountains of Montana. The wings of this female extended beyond
the ends of the femora indicating exceptional powers of flight for the
species. In the 1920 outbreak on rangeland of British Columbia, high numbers
moved in August from areas of drought-stricken vegetation to areas of green
Adults of the Bruner slantfaced grasshopper are colorful, medium-sized
grasshoppers (Fig. 5 and 6). The head has a
slightly slanted face; antennae are filiform; a vertical ivory band runs
from base of the antenna to the base of clypeus and mandible; an ivory
or pale tan streak runs from rear of eye onto the lateral carina of the
pronotum (See Figure 4). A common color
pattern of the dorsum of head and the pronotal disk is shown in Figure
7. Pronotum with median carina incised once. Wings are long, extending
approximately to end of hind femur and as much as 2 mm longer; tegmen with
prominent spots and an ivory streak near front edge. Medial area of hind
femur with three light spots in the dark dorsal stripe; tibia orange or
red. Color patterns are variable and may differ from the common pattern
described. A conspicuous pattern is an immaculate tan dorsum from head
to end of abdomen in both nymphs and adults (Fig.
The nymphs are identifiable by their color patterns, structures, and
shape (Fig. 1-4):
1. Head with slanted face; ivory or pale tan vertical bar present on
face running from base of antenna to base of clypeus and mandible; ivory
or pale tan streak running from rear of eye onto lateral carina and disk
of pronotum; antennae filiform; lateral foveolae oblong.
2. Pronotum with lateral lobe of instar I colored tan and spotted fuscous,
lateral lobe of instars II-IV with large fuscous marking and often with
ivory spot near center; median carina entire in instars I and II, incised
once near middle in instars III and IV.
3. Hind femur with dorsal stripe of medial area nearly solid fuscous
in instar I; three light spots in stripe faint in instar II, distinct in
instars III and IV. Hind tibia of instars I and II fuscous, of instars
III and IV straw-colored.
4. Venter of abdomen and thorax ivory, yellow, or pale tan.
Hatching of the Bruner slantfaced grasshopper occurs in June in both the
northern mixedgrass prairie and the meadows of the Big Horn Mountains and
the Laramie Range. In mountain habitats time of hatching varies due to
yearly variations in snow depth and spring meltdown and their effects on
soil temperatures. In 1994, in a meadow of the Laramie Range, hatching
began on June 11, but in 1995 a late summer delayed hatching until June
30. The hatching period is short, lasting only two weeks in both Wyoming
and Montana. No research of embryonic development has been conducted, but
field observations suggest that the species may have a two-year life cycle
in mountain meadows and northern grasslands.
The nymphs emerge over a period of two weeks. In their mountain and foothill
habitats, grasses remain green and supply an abundance of nutritious food.
Cold temperatures and frequent cold rains and snow retard their development.
The nymphal period, nevertheless, is relatively short, ranging from 40
to 46 days. Only four nymphal instars are required by the species to reach
the adult stage.
Adults and Reproduction
Adults normally appear in July in the northern mixedgrass prairie and in
mountain meadows. Seasonal temperatures greatly influence the precise time
of eclosion. In a mountain meadow of the Laramie Range, adults first appeared
14 July 1994, but in 1995, which was a seasonally late year, they did not
appear until August 10. The period of eclosion lasted 21 days in 1994 and
16 days in 1995, suggesting that the grasshoppers were exposed to warmer
temperatures later in the summer and were partially making up for the retardation
of their earlier stages in 1995.
The adults remain in the same habitat in which the nymphs hatched and
developed. The habitat provides green grass for food, ground litter for
shelter, and interspersed bare ground for basking and oviposition.
Meager information is available on mating, maturation, and oviposition.
Observations are impeded by the extended duration of basking and evidently
the short time they spend in other activities essential for their survival.
A Montana study indicated that in the northern mixedgrass prairie, oviposition
begins approximately 18 days after the first appearance of adults and continues
into late September. In mountain meadows an early, heavy snowfall in August
will be lethal, but in a year with a late fall individuals persist into
early October, lengthening the oviposition period.
Caged females oviposit freely into containers of bare soil collected
from their habitat. Examination of five pods revealed 2 to 10 eggs per
pod with an average of six. The unusual variation in number of eggs per
pod may have been caused by the change in temperature from the mountain
environment to the laboratory cage. Average temperatures in the cage were
72°F at night and 82°F during the day. Pods are 1/2 to 5/8 inch
long and are inserted diagonally into the soil. The top of the pod lies
1/4 to 3/8 inch below the soil surface. The pod wall is thick and strong
(Fig. 9). Eggs are yellow and 5.5 to
6.4 mm long. They are surrounded by pale tan froth and topped with 1/16
to 1/8 inch of offwhite froth.
No specific research of the population ecology of the Bruner slantfaced
grasshopper has been conducted. A few facts, however, can be gleaned from
general studies of grasshoppers. During irruptions this species may be
the dominant member of an assemblage. In the 1920 outbreak on more than
2,000 square miles of rangeland in British Columbia, the Bruner slantfaced
grasshopper contributed 50 percent of the assemblage, Camnula pellucida
30 percent, and several species the remaining 20 percent. No measurements
of density were taken early in the year, but in August during a drought,
the grasshoppers moved to areas with green vegetation in which the concentration
of the Bruner slantfaced grasshopper measured 720 to 900 individuals per
square yard. In meadows of the Big Horn Mountains this species may also
rise to dominance. In one meadow in 1991, it was the dominant member in
an assemblage of four species. Densities of young adults per square yard
were estimated to be: Bruneria brunnea, 8.9; Melanoplus bruneri,
3.7; Camnula pellucida, 3.1; and Chorthippus curtipennis,
0.3. Of the 21 meadow sites surveyed for grasshoppers in 1991 in the Big
Horn Mountains, the Bruner slantfaced grasshopper was dominant in one,
co-dominant in three, and subdominant in 17. In the latter 17 sites, densities
of this species ranged from 0.05 to 0.8 and averaged 0.3 young adults per
square yard. Apparently in the many disjunct meadows of the Big Horn Mountains,
the population ecologies of this grasshopper are separate and may differ
The Bruner slantfaced grasshopper is a geophilous species spending its
time on the ground surface during the day and hidden in ground litter at
night. None can be found in early morning on either the vegetation or on
the ground surface. One successful observation of the location of their
shelter was made. A male nymph (instar IV) was discovered 1/2 inch deep
in ground litter of a meadow in the Big Horn Mountains on 21 July 1994
at 6:12 a.m. DST; the soil surface temperature was 35°F and air temperature
34°F. The nymph was immobile and sitting horizontally on a layer of
grass litter and was completely covered by litter.
Two hours after sunrise, individuals begin to appear on the ground surface.
They rest horizontally on bare ground or on ground litter and bask. During
basking they present a side perpendicular to the sun and lower the associated
hindleg to expose the abdomen more fully. Basking continues for approximately
three hours before they become active. The feeding of a male was noted
at 10:55 a.m. on 4 August 1994. Other activities probably commence at this
time but were not observed. A second period of basking occurs in the afternoon.
Shortly before sunset, when soil temperatures have not yet cooled much
(65°F to 70°F), the grasshoppers seek shelter for the night.
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Larsen, J.C., J. A. Hutchason, T. McNary, and K. Zimmerman. 1988-94.
The Wyoming Grasshopper Information System. Cooperative Agricultural Pest
Survey. University of Wyoming, Laramie.
Lockwood, J.A., J.C. Burne, L.D. Debrey, R.A. Nunamaker, and R.E. Pfadt.
1990. The preserved fauna of grasshopper glacier (Crazy Mountains, Montana):
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development of range grasshoppers as related to control. USDA ARS Entomol.
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Treherne, R.C. and E.R. Buckell. 1924. The grasshoppers of British Columbia
with particular reference to the influence of injurious species on the
range lands of the province. Bull. Can. Dept. Agric. n.s. 39: 1-47.
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insects of Canada and adjacent regions. Lyman Entomol. Mus. Res. Lab. Mem.
13 Vol. 2.
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