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The pallidwinged grasshopper, Trimerotropis pallidipennis (Burmeister), ranges from southwestern Canada to Argentina, making it the most widely distributed bandwinged grasshopper in the New World. In North America the primary habitats of this grasshopper lie in the deserts of the West where populations irrupt sporadically to damaging numbers. Vegetation of habitats consists of shrubs, forbs, and grasses with a preponderance of bare ground on which these grasshoppers commonly bask and rest. Outside their usual rangeland habitats, pallidwinged grasshoppers find favorable environmental conditions in weedy city lots.
Over a period of 29 years, 1952 to 1980, six outbreaks of the pallidwinged
grasshopper occurred in Arizona. These outbreaks have been brief, one lasted
two years and the other five lasted only one year. Similar short outbreaks
have occurred in the deserts of New Mexico, Utah, and California.
The most recent outbreak took place in west central Arizona in 1998.
During the night of April 19 swarms attracted to city lights landed from
Lake Havasu City to Bullhead City, a distance of approximately 50 miles.
Crushed by traffic on streets and highways, the grasshoppers caused cars
and trucks to skid and slide. Accumulations of the grasshoppers around
buildings reached a depth of 2 inches.
The pallidwinged grasshopper is a relatively large rangeland grasshopper, but one that varies in weight depending on environmental conditions of its habitat. Live weight of males collected in the Sonoran Desert west of Phoenix, Arizona averaged 268 mg and females 565 mg while males collected in a sagebrush habitat along a hillside above the Gunnison River in Colorado (elevation 1,746 ft.) averaged 175 mg and females 429 mg. Live weight of six young males caught 14 May 2001 in the desert near Mesa, Arizona averaged 261 mg and four immature females 399 mg (dry weight: males 100 mg, females 145 mg).
A variety of diets has been revealed by several studies of crop contents.
In a four-year study, 1966-1969, in south-central Idaho, examination of
153 crops of the pallidwinged grasshopper revealed that 63 percent of crops
contained fragments of downy brome and 22 percent tumblemustard. Other
plants detected in the crops ranged from a trace to 11 percent. The grasses
included crested wheatgrass, thickspike wheatgrass, and Sandburg bluegrass.
The forbs included milkvetch, western salsify, big sagebrush, hoary aster,
Greene rabbitbrush, and gray rabbitbrush. Also found in crops were fragments
of arthropod parts, fungi, and pollen.
Crop analysis of adults collected in southwestern Texas near Alpine
in the summer of 1974 showed that forbs were more frequently ingested (64
percent) than grasses (36 percent). However, blue grama grass was the most
often ingested single plant, 23 percent, followed by a forb, Cryptantha
sp, 16 percent. Other grasses found in crops included Leptoloma cognata
(7 percent) and Setaria sp (1 percent); other forbs included Solarium
sp (11 percent), Iva sp (10 percent), with smaller percentages of
Croton sp, Gaura sp, and Ratibida sp.
In the Sonoran Desert, 30 miles west of Tucson, Arizona, 68 of 126 crops (54 percent) contained needle grama, six crops contained the forb Allionia incarnata, four crops contained the forb Franseria deltoidea, and three crops contained arthropod parts.
Although these studies indicate a high degree of polyphagy by the pallidwinged grasshopper, two-choice tests demonstrate that the species has food preferences. Laboratory tests of 15 plant species offered in pairs to adults collected in Millard County, Utah in 1998 revealed preferences for dandelion, kochia, downy brome, crested wheatgrass, and needleandthread.
One of the few observations of actual flight of this species was made in Nevada; where flights were often of long duration, individuals commonly ascending well out of sight. In one case, a male circled about a sagebrush slope for 17 minutes in a single flight before finally coming to rest. In the Phoenix, Arizona area (altitude 1083 feet), pilots have reported swarms at altitudes of 3,000 to 5,000 feet. Flushed grasshoppers fly swiftly at heights of 2 to 3 feet often going more than 100 feet and beyond sight.
A remarkable dispersal record of the species was made 7 September 1966
when adults were discovered along roadsides bordering a sugar plantation
at Ewa, Oahu, Hawaii. Specimens sent to the U.S. National Museum were identified
by A. B. Gurney. The Hawaiian infestation persisted in 1967 and 1968. Probable
source of the infestation was western North America indicating wind transportation
of a swarm.
The pallidwinged grasshopper is a moderately-sized tan or gray insect (Fig. 6 and 7) found chiefly in desert and semidesert habitats. The tegmen bears two transverse dark bands that cross its entire width; the distal end bears numerous brown spots. The center of the hindwing has a relatively narrow but conspicuous black band; the wing disk ranges from white to pale yellow, and the apical area is transparent (Fig. 8). Incised twice near the front, the median carina of the pronotum is high on the prozona and low but distinct on the metazona. The ventral edge of the pronotal lobe is straight, bearing no tooth. The inner medial area of the hind femur is black, broken by two yellow bars (Fig. 9). The hind tibia is yellow. The venter is solid cream to pale yellow.
The nymphs are identifiable by their structures and color patterns (Fig. 1-5).
1. Head with distinct triangular foveolae; carinae of frontal
costa straight in instar I and II, carinae slightly incurving at level
of antennal sockets in instars III to V; carinae connected by a bridge-like
ridge approxi- mately at level of antennal sockets in all instars.
2. Pronotum with distinct median carina feebly incised
twice in instar I, becoming more strongly elevated and clearly incised
in instars II to V; disk rugose on prozona, smooth on metazona; median
carina elevated on prozona, low on metazona.
3. Hindleg: in instar I mainly black except basal fourth
of femur (outer area) pale, inner medial area black with pale distal bar;
hind tibia black with pale basal annulus; tarsus white except segment two
and distal half of last segment black. In instar II medial area of hind
femur pale tan, two dark bars on upper marginal area, inner medial area
of hind femur with three black and three pale tan bars; hind tibia black
or pale tan. In instars III to V outer and inner surface of hind femur
pale tan with two or three black bars; hind tibia yellow.
4. Ground color tan spotted brown; venter yellow or olive.
In nature rainfall appears to be a critical factor for eggs to survive and hatch. In the Tule Hill site of Millard County, Utah, a moderate population of adults inhabited the site in the summer of 1998, but no eggs hatched by 22 June 1999 apparently having died because of drought.
In a study conducted in an outdoor screened insectary at Mesa, Arizona, researchers found that female nymphs have five or six instars, while the males usually have five but a few have six. The study also found that the nymphal period of grasshoppers reared at relatively low temperatures in the laboratory (range 70° to 84°F, mean 77°F) averaged 50 days for males and females with five instars and 60 days for females with six instars. The nymphal period of grasshoppers reared during mid summer in the outdoor insectary at relatively high temperatures (range 81° to 101°F, mean 91°F) averaged 31 days for the males and 33 days for the females.
During the day adults fly about and may disperse widely. In the Alpine, Texas study marked adults were recaptured for only 14 days. On the other hand, in a small favorable habitat of about one acre in the desert of Millard County, Utah, adults have been found in residence from 19 June to 29 August 1998, indicating a habitat fidelity of at least 67 days.
Males make frequent local flights in which they crepitate (snapping sounds produced by the hind wings). Observations indicate that crepitation initiates pair formation of the sexes. Upon landing, the male walks in a straight line to a resting female. Courtship consists of ordinary stridulation which resembles a trilling sound to the human ear. One to eight trills in quick succession are produced by males advancing toward females. A receptive female remains still as the male approaches, mounts, and attaches his genitalia to consumate mating.
Reproductive maturation of females in nature has not been closely followed. However, in south-central Arizona adults that fledged by the end of April in a habitat of succulent vegetation bore well-developed eggs a week later, but no eggs were found in females inhabiting dry desert.
Caged in pairs and sheltered in a screened insectary during mid summer (76° to 101°F, mean 88°F), and fed a mixed diet of four species of host plants, pallidwinged grasshoppers exhibited a high fecundity, comparing favorably with other pest species of grasshoppers. Sixteen females averaged 386 eggs each. One female laid a record 27 pods containing 955 eggs. The preoviposition period was long with a minimum of 26 days and an average of 43 days. Average longevity of these females was 80 days. In nature the eggs are laid in bare soil to a depth of approximately 1 inch. The pod is slightly curved, narrow (1/8 inch in diameter), and 1 inch long (Fig. 10). Each pod contains an average of 34 pale yellow eggs, 4.5 to 5 mm long.
Barnes, O.L. 1963. Observations on the life history of the desert grasshopper (Trimerotropis pallidipennis pallidipennis) in laboratory and insectary cages. J. Econ. Entomol. 56: 525- 528.
Chappell, M.A. 1983. Thermal limitations to escape response in desert grasshoppers. Anim. Behav. 31: 1088-1093.
Joern, A. 1983. Small-scale displacements of grasshoppers (Orthoptera: Acrididae) within arid grasslands. J. Kansas Entomol. Soc. 56: 131-139.
Massion, D.D. 1983. An altitudinal comparison of water and metabolic relations in two acridid grasshoppers (Orthoptera). Comp. Biochem. Physiol. 74A: 101-105.
Otte, D. and A. Joern. 1977. On feeding patterns in desert grasshoppers and the evolution of specialized diets. Proceed. Acad. Nat. Sci. Philadelphia 128: 89-126.
Scoggan, A.C. and M.A. Brusven. 1972. Differentiation and ecology of common immature Gomphocerinae and Oedipodinae (Orthoptera: Acrididae) of Idaho and adjacent areas. Melanderia 8: 1-76.
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