Entomology
Twostriped Slantfaced Grasshopper
Mermiria bivittata (Serville)
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Distribution and Habitat
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Wyoming distribution map
The twostriped slantfaced grasshopper is widely distributed in North America. Its
center of distribution is in the tallgrass prairie where it may reach densities of
one adult per square yard in unplowed native grassland. Its habitat consists primarily
of tall grasses: big bluestem, yellow indiangrass, and switchgrass, and it frequently
inhabits these grasses on slopes and hills. Small, edaphic stands of tall grasses
in the mixedgrass, shortgrass, bunchgrass, and desert prairies also provide suitable
habitats for the species. In addition, this grasshopper may live in luxuriant stands
of midgrasses in the mixedgrass prairie.
Economic Importance
The twostriped slantfaced grasshopper is a frequent and common species in the tallgrass
prairie and is a potentially damaging pest. It feeds on valuable forage grasses and
occasionally reaches outbreak densities, as it did in native grass pastures of eastern
Kansas in 1939. It is a large grasshopper; live weights of males from eastern Wyoming
average 222 mg and females 784 mg (average dry weight of males 63 mg, females 204
mg). An estimate of damage indicates that an individual consumes 3.4 gm dry weight
of grass during its lifetime, an amount greater than the bigheaded grasshopper, Aulocara
elliotti, which consumes 2.0 gm. Nevertheless, it rarely becomes a significant pest
because densities usually remain light and grass production plentiful in the tallgrass
prairie.
A quantitative study of the impact of grasshoppers on tallgrass prairie disclosed
no significant differences in above ground biomass of vegetation between plots with
five grasshoppers per square yard and plots with 11 grasshoppers per square yard (early
instars). In these studies the twostriped slantfaced grasshopper was a subdominant
in an assemblage of 15 species in which Phoetaliotes nebrascensis, a grass feeder,
was the dominant species. These data indicate that in the tallgrass prairie where
grasshopper densities are lower and vegetation production higher than in the drier
western grasslands, the impact of grasshoppers is slight and often unmeasurable.
Food Habits
The twostriped slantfaced grasshopper is a grass feeder. Enjoying a wide distribution
in North America, the species exploits a variety of grasses that grow in its diverse
habitats. In the tallgrass prairie of eastern Kansas, examination of crop contents
has shown that it feeds upon sideoats grama, tall dropseed, and yellow indiangrass;
in the northern mixedgrass prairie of western Nebraska, it feeds upon prairie sandreed,
western wheatgrass, big bluestem, and on eight other grass species; in the blackland
(tallgrass) prairie of northeastern Texas, it feeds upon big bluestem, silver beardgrass,
prairie dropseed, and several species of grama. This grasshopper has been found to
feed on a total of 18 species of grass and on threadleaf sedge. Its dietary, in addition
to the grasses already mentioned, includes little bluestem, sand bluestem, blue grama,
downy brome, smooth brome, sand dropseed, needleandthread, and hairy grama. Preference
tests of caged individuals in a Texas insectary showed that the grasshoppers chose
Bermuda grass, an introduced species, and prairie dropseed for food in preference
to big bluestem and silver beardgrass.
The twostriped slantfaced grasshopper feeds on green leaves of its host plant. It
may attack a plant in three ways. First, sitting vertically, head- up, and near the
middle of a wide leaf (sand bluestem), it holds onto its food with the front tarsi
and eats from the edge to the midrib, progressing toward the tip. Nymphs and young
adults consume lengths of leaf 1 to 2 inches long, causing characteristic semi-elliptical
damage. In the second method of attack, the grasshopper, also in a vertical, head-up
position, cuts a narrow leaf (needleandthread) near the tip and holds onto a 1 to
2 inch section with the front tarsi and consumes the whole section. The third method
of attack involves the grasshopper feeding on a bent over or recumbent leaf from a
horizontal orientation. It then progresses from the middle of the leaf for a short
distance toward the base. Feeding bouts of the adults last as long as 7 to 10 minutes.
By the end of the season the culms of sand bluestem are stripped of nearly all their
leaves and the bunch-like leaves of young plants are partially consumed.
During feeding, the twostriped slantfaced grasshopper may cut and drop sections of
leaf, which can still be found on the ground around each plant at the end of the season.
In the tallgrass habitat, unlike the mixedgrass prairie, the cut leaves remain uneaten
by grasshoppers and become part of the ground litter.
Dispersal and Migration
The twostriped slantfaced grasshopper has long wings that extend to the end of the
abdomen. It is a strong and adept flyer. In flushed flights it flies distances of
2 to 12 feet at heights of 9 to 36 inches. The flight is silent and may be straight
or sinuous. The grasshopper usually takes off from vegetation and lands on vegetation,
but it may also land on plant litter or bare ground. It is able to turn at the end
of a flight to land vertically on an upright culm or stem. It can also veer in flight
to land within vegetated areas, although many individuals occasionally land in inimical
bare areas.
No special study of its dispersal or migration has been made. It has not been found
as an "accidental" in the mountains west of Boulder, Colorado, even though it inhabits
the adjacent plains and foothills. Although direct evidence of its dispersal is lacking,
we may speculate that the species does disperse for the following reasons: 1) good
capacity for flight; 2) extensive range in North America; and 3) occupation of small
edaphic habitats in the drier grasslands.
Identification
The twostriped slantfaced grasshopper is a large, long-winged, colorful insect (
Fig. 6 and 7). It has a strongly slanted face; the antennae are ensiform. A brown stripe beginning
behind the compound eye runs along the side of the head and onto the lateral lobe
of the pronotum. Four diagnostic characters of this species are: 1) the disk of the
pronotum rounds off onto the lateral lobe, i.e., it lacks lateral carinae (
Fig. 8); 2) the pronotal disk margin is cut by three sulci; 3) sides of occiput and pronotal
disk without ivory stripe; and 4) one longitudinal white or ivory streak on tegmen.
The hind tibiae are orange and the body is tan, often densely spotted brown (visible
under low magnification). In the West, this grasshopper broadly overlaps geographically
and seasonally with two other species of the genus -
M. picta and
M. texana. All three look superficially alike, but adults can be easily separated by a few
distinguishing characters.
Mermiria texana has an ivory stripe on sides of occiput and pronotal disk and it has two longitudinal
white streaks on the tegmen, one above base of hindleg and one above abdomen. Mermiria picta lacks the ivory stripes on the occiput and pronotal disk and the streaks on tegmen
(M. bivittata has one streak), and it has well-developed lateral carinae on pronotal disk and the
lateral carinae are cut by two posterior sulci (the anterior sulcus is visible on
pronotal disk but does not cut the carinae). One other species is known, M. intertexta. It is distributed in the eastern United States along the Atlantic and Gulf coasts.
The nymphs (Fig. 1-5) are identifiable by their color patterns, structures, and shape:
1. Head with face strongly slanted; antennae ensiform with proximal segments triangular
in cross section, distal segments tubular; lateral foveolae triangular, invisible
from above; narrow brown band beginning behind compound eye runs along side of head
and continues on dorsal edge of lateral lobe; band faint in early instars.
2. Pronotum with lateral margin of disk rounding off onto lateral lobe; margin of
disk cut by three sulci; sulci weak in instar I.
3. Hind femur with upper medial area darker than the lower; hind tibia yellow or pale
gray.
4. Body yellow, tan, or green and densely spotted brown (visible with low magnification).
Hatching
The twostriped slantfaced grasshopper is a late-hatching species. In the tallgrass
prairie of eastern Kansas, first instars appear in early May, while in the mixedgrass
prairie of eastern Wyoming they do not appear until early to mid June. The period
of hatching in a habitat may last two weeks or longer.
Nymphal Development
Although nymphs hatch late and normally experience warm conditions and favorable food
supply, they develop at a relatively slow rate. Their minimum nymphal period, completed
by the males, is 40 days. The slow development is probably due to exposure to the
cooler temperatures of their luxuriant grass habitat and their above-ground location
on tall grass. Studies carried out in eastern Wyoming indicate that the males have
four instars and the females five. Because of their smaller size, the males apparently
require fewer instars to achieve the weights necessary to metamorphose to the adult
stage than do the much larger females. This proposition suggests that the males have
a shorter nymphal period and thus emerge before the females.
Adults and Reproduction
Most adults remain in the habitat in which they hatched and developed as nymphs. There
they have the tall grasses for feeding, roosting, and shelter and bare ground for
oviposition. Several observations of male courtship have been made. On approaching
a female, a male stridulates with a burst of two to five strokes of the femora. No
information is available on mounting and copulation nor on how soon adult females
mate and lay eggs. The females oviposit in bare ground near their host plant. Eggs
are placed deep in the soil, lying at depths between one and one-quarter and one and
three-quarters inches. The egg mass, which consists of 14 to 18 eggs, has no pod wall;
the eggs are held together by spots of froth (
Fig. 9). The egg mass itself is one-half inch long. Eggs are tan or two-toned tan and yellow
and are 7.2 mm long. A long froth plug of one and one-quarter inches lies above the
eggs. The diameter of the plug measures one-eighth inch or slightly more.
Population Ecology
Studies on the population ecology of the twostriped slantfaced grasshopper have been
conducted in the tallgrass prairie where the species finds extensive areas of its
preferred habitat of tall grasses. These studies show that populations fluctuate around
low densities, rarely exceeding one adult per square yard. Food supply is not the
limiting factor, as the luxuriant grass foliage of the tallgrass prairie remains plentiful
except in cases of heavy use by livestock. Elegant studies of the impacts of burning,
which occurs regularly via humans and lightning, show that the grass habitat is maintained
by reducing competition or invasion by forbs and shrubs thereby favoring the graminivorous
grasshoppers over the forb- or mixed-feeders. A problem that still remains unsolved
is the discovery of the factor or factors that limit the size of populations of the
twostriped slantfaced grasshopper.
Daily Activity
The twostriped slantfaced grasshopper is a phytophilous species spending most of its
days and nights perched on grass. At night, nymphs and adults rest vertically head-up
on leaves or culms at heights of 8 to 12 inches. As the sun rises and rays strike
their perches, the grasshoppers begin to bask by adjusting their positions so that
one side receives the full benefit of the radiant heat. They may bask for two to four
hours before they begin to feed or move about on host plants. Movement consists of
descent by backing down from their perches, crawling onto another leaf, or jumping
from one plant to another. If in jumping they land on the ground, they immediately
crawl up on a nearby grass plant. As do grasshoppers of other species, they frequently
preen their antennae and compound eyes, presumably to remove dust particles that settle
on these organs. High temperatures cause them to change their positions on grass plants
to the shady side. When temperatures subside they again become active, feeding and
moving about. As evening approaches, they become quiescent and remain largely immobile
from 8:30 p.m. to 7 a.m. DST. Rain and cool temperatures extend quiescence. Individuals
continue to rest on their nocturnal perches until the sun again shines on them.
In the sandhills grassland of central Nebraska, a study of time and activity budgets
of this grasshopper showed that in the daylight hours (13.5 hours), the twostriped
slantfaced grasshopper remained quiescent 88 percent of the time, fed 10 percent,
and moved 1 percent.
Selected References
Brusven, M. A. 1967. Differentiation, ecology and distribution of immature slant-faced
grasshoppers (Acridinae) in Kansas. Kansas Agr. Exp. Stn. Tech. Bull. 149.
Campbell, J. B., W. H. Arnett, J. D. Lambley, O. K. Jantz, and H. Knutson. 1974. Grasshoppers
(Acrididae) of the Flint Hills native tallgrass prairie in Kansas. Kansas Agr. Exp.
Stn. Research Paper 19.
Evans, E. W. 1988. Grasshopper (Insecta: Orthoptera: Acrididae) assemblages of tallgrass
prairie: influences of fire frequency, topography, and vegetation. Can. J. Zool. 66:
1495-1501.
Mulkern, G. B., K. P. Pruess, H. Knutson, A. F. Hagen, J. B. Campbell, and J. D. Lambley.
1969. Food habits and preferences of grassland grasshoppers of the North Central Great
Plains. North Dakota Agr. Exp. Stn. Bull. 481.
Isely, F. B. 1938. The relations of Texas Acrididae to plants and soils. Ecol. Monogr.
8: 551-604.
Joern, A., R. Mitschler, H. O'Leary. 1986. Activity and time budgets of three grasshopper
species (Orthoptera: Acrididae) from a sandhills grassland. J. Kansas Entomol. Soc.
59: 1-6.
Otte, D. 1970. A comparative study of communicative behavior in grasshoppers. Misc.
Publ. Mus. Zool., Univ. Michigan, No. 141.
Wilbur, D. A. and R. F. Fritz. 1940. Grasshopper populations (Orthoptera, Acrididae)
of typical pastures in the bluestem region of Kansas. J. Kansas Entomol. Soc. 13:
86-100.
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