Brownspotted Grasshopper
Psoloessa delicatula (Scudder)
Link directly to photos of adults, nymphs,
or eggs.
Distribution and Habitat
P. delicatula continental distribution map
Wyoming distribution map
The brownspotted grasshopper inhabits the grasslands of the western
states and provinces. It is a common early denizen of desert shortgrass,
mixedgrass, and bunchgrass prairies and extends its distribution into western
desert shrub communities where grasses form a sparse understory. It does
not invade mountain grasslands, but is present in foothill habitats as
high as 8,076 feet.
Economic Importance
The brownspotted grasshopper feeds on grasses and sedges. When adults are
abundant in spring, they cause some of the first grasshopper damage to
rangeland. Populations of adults in the mixedgrass prairie may reach densities
of 30 grasshoppers per square yard and maintain high densities for three
or more years. Normally, populations of adults range from 0.5 to 1 grasshopper
per square yard and cause no significant damage. This grasshopper is in
the smallest group of the three size divisions of rangeland grasshoppers.
Live weights of males average 99 mg and of females 284 mg (dry weight:
males 32 mg, females 90 mg). Quantitative assessment of damage by this
species has not been undertaken.
Food Habits
Host plants of the brownspotted grasshopper consist almost entirely of
grasses and sedges. When the overwintered nymphs become active in early
spring, they feed mainly on needleleaf and threadleaf sedges, plants that
start seasonal growth very early. The nymphs feed also on cool- season
grasses: western wheatgrass, downy brome, and sixweeks grass. As the season
progresses and the grasshoppers become adults, they feed more on warm-season
grasses, especially blue grama and sand dropseed. Examination of gut contents
and direct observations have provided records of the brownspotted grasshopper
feeding at various times and places on two species of sedges and 14 species
of grasses. It may ingest in minute amounts forbs, lichens, moss, and arthropods.
The brownspotted grasshopper has two methods of attacking a grass or
sedge. The first approach is to climb a short distance up the leaf and
start cutting the leaf by eating through it. The grasshopper then holds
onto the cut portion with the front tarsi and feeds on the entire leaf
to the tip. The second method is for the grasshopper to raise its head
and cut through a leaf, recover the fallen leaf on the ground, and then
feed on it from the cut end to the tip. In the first method the grasshopper
is upright, clinging to the leaf with mid- and hindlegs, and in the second
method the grasshopper sits horizontally on the soil surface and litter,
the mid and hind tarsi in contact with the ground, while the front tarsi
handle the cut leaf. This grasshopper also feeds on ground litter, usually
green or dry grass leaves, and on recumbent attached grass leaves.
Dispersal and Migration
Adults of the brownspotted grasshopper possess long wings that extend beyond
the end of the abdomen. These provide the adults with strong powers of
flight for evasion of predators and for dispersal. After sunrise, three
to four hours of basking are required before flight is possible. Evasive
flights are silent and sinuous for distances of 5 to 9 feet at heights
of 4 to 6 inches. The end of a flight often comes with a quick turn in
direction and sudden drop to the ground. The grasshopper lands horizontally
on the surface and may face the intruder. No records of this grasshopper
migrating have been published. Collection of a solitary female on a lawn
in Laramie, Wyoming, at a distance of 1 mile from the nearest rangeland
habitat provides some evidence that dispersal occurs.
Identification
Adults of the brownspotted grasshopper are small and colored dull gray
and brown with dark brown spots and maculations (Fig.
6 and 7). Head with face slightly slanted; frontal costa grooved (Fig.
9); lateral foveolae well-defined and square to oblong. Pronotum with
distinct median carina cut once in front of middle; lateral carinae constricted
in middle, deeply cut, and strongly depressed in region of cut; lateral
lobes with rounded broad ridge that runs diagonally upward; lower on the
lateral lobe, a smaller, oblique ridge is present; it runs in the opposite
direction and is often conspicuously colored ivory. Hind femur with triangular
marking on upper marginal area; hind tibia proximally pale gray with brown
spots, distally orange.
Nymphs (Fig. 1-5)are identifiable by their
shape, external structures, and color patterns:
1. Head with face slightly slanted and with front of fastigium appearing
rounded; frontal costa grooved; lateral foveolae square to oblong; each
side of vertex with a curved brown stripe that may extend short distance
on pronotum (Fig. 8). Antennae filiform
(threadlike).
2. Pronotum with definite median carina, entire (uncut) in instar I,
cut in instars II to V; lateral carinae distinct and slightly constricted
in instar I, strongly constricted, cut and depressed in instars II to V;
lateral lobe with rounded broad oblique ridge faintly evident in instar
I and becoming larger in subsequent instars; usually a distinctive pale
yellow, oblique ridge present on lower rear of lobe (see Figure
4 for a clear picture).
3. Hind femur with rudimentary triangular maculation on upper marginal
area. Hind tibia pale gray and brown.
4. General body color of nymphs is pale tan to brown with dark brown
markings and with a light band on dorsum from head nearly to end of abdomen
(Fig. 8). Older instars become darker,
colored brown and gray with dark brown markings (Fig.
1-5).
To compare early instar nymphs of Psoloessa delicatula with two
similar species, click here.
Hatching
Rearing the brownspotted grasshopper in outdoor cages indicates that this
species has a two-year life cycle in central Saskatchewan (Fig.
11). The eggs remain viable but unhatched during the summer in which
they are laid, and hatch during the second summer at a time when most rangeland
grasshoppers are mature and reproducing. The eggs are exposed to warm soil
temperatures of their first summer and to low soil temperatures of winter.
They perhaps break diapause during the winter cold period. The presumed
timing of this event raises the question as to why hatching is delayed
during their second summer. In the southern range of the species, eggs
appear to hatch the same summer in which they are laid. Unknown is the
location of the line or zone between life cycles of one year and two years.
Further study of the embryological development and life cycle of this grasshopper
is desirable. For a small grasshopper, eggs lie relatively deep in the
soil (three-quarters to one and one-quarter inches). The period of hatching
lasts from two to six weeks.
Nymphal Development
Nymphal development is slow and extended. In the Pawnee National Grassland
of northeastern Colorado, for example, eggs start to hatch in early July
and nymphal development proceeds through summer and fall for about 120
days. As temperatures decrease and days become shorter in fall, greater
numbers of nymphs take shelter and begin winter dormancy. Cold weather
in November compels all nymphs, mainly fourth and fifth instars by this
time, to seek refuge under ground litter and bury shallowly in the soil.
Spells of unseasonably warm weather in winter cause some individuals to
become active for brief periods. After hibernating through the winter,
the nymphs resume development in April and reach adulthood during this
and the next month.
Adults and Reproduction
The adults remain in the same habitat in which the eggs and nymphs develop.
Even though the first group of host plants mature and dry, food resources
remain plentiful. The adults feed increasingly on the vigorously growing
warm- season grasses as summer progresses. A few weeks after fledging,
the grasshoppers mate. Observations of mating pairs have been made during
morning hours (9 to 11 a.m. DST), in June and early July. A male seeking
a mate stridulates, sending two to four acoustical signals, while advancing
on a female. When close, he mounts and attempts to copulate. The female
may accept him or reject him by emitting a series of ticking sounds (produced
by the hind tibiae kicking out and striking the ends of her tegmina).
A gravid female ready to oviposit selects a site of bare soil. Boring
over an inch into the soil, she deposits 18 eggs and surrounds them with
very little froth but forms a three-quarter inch froth plug above them.
The whole pod measures around one and one-half inches (Fig.
10). The eggs are yellow and 4.9 mm long.
Population Ecology
Although densities of the brownspotted grasshopper usually remain low (0.5
to 1.0 adults per square yard), they occasionally become very high in habitats
of the mixedgrass prairie (25 to 30 adults per square yard). Heavily infested
sites may encompass as much as four square miles. Causes of these population
outbreaks are unknown as no detailed studies of population dynamics have
been made over a sufficiently long period. Limited data indicate that mortality
rates of 5 to 6 percent per day of adults at both low and high densities
are similar to mortality rates of other rangeland grasshoppers. Large variations
in survival of overwintering nymphs have been observed, ranging from 46
to 100 percent.
Daily Activity
The brownspotted grasshopper is a ground-dwelling insect with an array
of behavior patterns that allow it to cope with both cold and hot temperatures
in its environment. During early spring, temperatures decline rapidly in
the evening, causing the nymphs to seek cover under grass litter where
they spend the night. In the morning, two to three hours after sunrise,
they begin to emerge from their shelters and bask on the soil surface by
exposing their sides to the warming rays of the sun. The nymphs bask for
long periods, three to four hours. During the latter part of this time
they may feed on ground litter, when the soil temperature has reached 70°F,
even if air temperature an inch above the ground is still low (54°F).
Normal activity of the nymphs begins late in the morning and ends early
in the afternoon. They may begin basking by 3:30 p.m. and start taking
cover by 5:30 p.m. DST.
Although the adults experience warmer weather in May and June, their
body temperatures fall at night and may be no greater than 40°F at
sunrise. Under these cold conditions they sit immobile on the surface of
the soil or litter. When the sun strikes the habitat, they turn their sides
perpendicular to the sun's rays and bask for as long as three hours. When
soil temperatures reach 75°F they may begin normal morning activities
of feeding, mating, and ovipositing. Air temperatures above 77°F cause
them to begin moving into shade, while air temperatures above 90°F
cause them to actively seek shade. They rest on the ground surface in the
shade of small shrubs or clumps of grass, and assume a "straddle" position
in which the hindlegs are spread away from the body. Six thermoregulatory
postures assumed by adults of this grasshopper have been described under
different environmental conditions. A seventh may be added, termed "squat,"
in which the basking grasshopper lowers its body and both flexed hindlegs
onto the soil surface. Adults end their day like the nymphs, basking in
the rays of the sun. Finally, they crawl under canopies of grasses in the
habitat for shelter during the night.
Selected References
Anderson, R. V., C. R. Tracy, and Z. Abramsky. 1979. Habitat selection
in two species of short-horned grasshoppers. The role of thermal and hydric
stresses. Oecologia 38: 359-374.
Otte, D. 1970. A comparative study of communicative behavior in grasshoppers.
Misc. Publ. Mus. Zool., Univ. Michigan. No. 141.
Pfadt, R. E. and R. J. Lavigne. 1982. Food habits of grasshoppers inhabiting
the Pawnee Site. Wyoming Agr. Exp. Stn. Sci. Monogr. 42.
Pickford. R. 1953. A two-year life-cycle in grasshoppers (Orthoptera:
Acrididae) overwintering as eggs and nymphs. Can. Entomol. 85: 9-14.
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