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The High Plains grasshopper inhabits the shortgrass prairie, a floral province dominated by shortgrasses, principally blue grama and buffalograss. In addition, this province supports a moderate amount of three or four species of midgrasses in any one locality. Common among these midgrasses are western wheatgrass, needleandthread, sand dropseed, red threeawn, and galleta hilaria. Also present in the shortgrass prairie are several sedges, forbs, and small shrubs along with much interspersed bare ground. The biogeographic map of the High Plains grasshopper shows an inner area (colored dark blue) where scouts found both nymphs and adults during the 1934-40 outbreak of the species and an outer area (colored pale blue) where they collected only adults. During the outbreak, swarms of the High Plains grasshopper dispersed widely from habitats of their origin. The species has been recorded infrequently in assemblages of rangeland grasshoppers during nonoutbreak years, yet it continues to survive and reproduce in especially favorable habitats. Such a habitat occurs in Otero County, Colorado, 5 miles southwest of Hawley. The area is characterized by sandy loam soil (Olney) with a 0 to 3 percent slope. Readily absorbing rainfall, the soil fosters an abundance of three midgrasses (sand dropseed, galleta hilaria, and red threeawn) in addition to the short grasses, (blue grama and ring muhly).
The feeding of five late instar nymphs and 13 adults was observed in their natural habitat (Hawley, Colorado) during the summer of 1997. Four nymphs and nine adults fed on sand dropseed, one adult fed on blue grama, and one on needleandthread. One nymph and an adult were observed feeding on ground litter. Although the grasshoppers were observed to taste leaves of nearby plants before feeding, no evidence was obtained of their moving to find particular species of grass.
Spring 1997 was very dry in Otero County, Colorado. When the majority of observations of feeding were made, sand dropseed had been grazed heavily by cattle and grasshoppers. Plants were short with stems grazed down to 1 to 3 inches, and most leaves were dry. The grasshoppers fed chiefly on the short stems that were still green. Evidently these conditions of sand dropseed made the plants convenient for High Plains grasshoppers to attack from their usual positions on the ground.
The common method of attack by a High Plains grasshopper was to walk up to a grass plant, taste it, and while remaining horizontal on the ground surface begin to feed at the tip of a low-lying leaf or on the stub of a grazed stem. When leaves were higher, the grasshopper raised up diagonally on the plant at approximately a 45° angle and began to feed on a leaf at or near the tip. The hindlegs remained on the soil surface, the midlegs on the plant, and the tarsi of the front legs handled the leaf conveying it to the mouthparts. Only once was a grasshopper observed feeding off the ground in the middle of a grass plant facing head down and feeding on a leaf or stem. The High Plains grasshopper appeared to be a very thrifty feeder as no clipping and dropping of leaves were observed. Laboratory observations revealed that whenever these grasshoppers severed a leaf, they held on to it and consumed all of the green but dropped the yellow, dry tissue.
Soon after transforming to the adult stage, the grasshoppers of dense populations begin to disperse. On their first flights, they cover from 25 to several hundred yards at a time and at heights of less than 50 feet. Later, the adults rise in swarms taking high, long flights that disperse the grasshoppers widely over great distances. Swarms appear to fly during both day and night; the lights of cities attract huge numbers and induce them to land. In 1937, 2,940 adults were marked with nontoxic paints to determine direction and distance of migratory flights. Sixteen grasshoppers were recovered 1 to 13 days later and at distances of 17 to 175 miles mainly in a northwest direction from the point of release. The results indicated that rate of movement ranged from 10 to 37 miles per day and that the grasshoppers flew with the prevailing winds. After the grasshoppers land in distant pastures, they concentrate into populations numbering about 20 per square yard. Fourteen days later the females begin to deposit eggs. At this time the adults no longer migrate, but they make regular low flights of one-half to 3 miles between egg beds and feeding grounds. Observations of small populations, less than one per square yard, in Otero County, Colorado in 1997 revealed that the adults form mating aggregations of approximately one adult per square yard on one-quarter to one-half acre of land. Three aggregations approximately 1 mile apart were discovered in an infested area of 6 square miles. As the whole area was not inspected, it is probable that several other aggregations were undetected.
Flushed flight is usually silent without crepitation, but a soft rustling of the wings is sometimes audible. Distances traveled ranged from 1 foot in early morning to more than 90 feet at midday at heights of 4 inches to 3 feet. The short flights are straight but the long flights are either straight or zig-zag and circuitous. Toward the end of a long flight, the grasshoppers may make a right angle turn before landing.
The nymphs are identifiable by their color, shape, and external structures (Fig. 1-6).
1 . Head with face nearly vertical; antennae filiform, majority of segments pale tan, terminal segments dark; lateral foveolae small and triangular; compound eyes tan or brown with light spots; usually narrow light band on side of head behind the compound eye.
2. Pronotum with median carina strongly elevated and incised once.
3. Hind femur with medial area tan and often with three transverse diagonal dark bars, inner medial area tan with two or three black transverse bars; hind tibia of instars I and II black with pale yellow annulus located proximally, instar III black and tan or entirely golden, instar IV, V, and VI golden.
4. General body color tan with brown round spots; venter generally immaculate cream to yellow.
The high pronotal crest and tan, heavily spotted body are diagnostic features of the younger nymphs. The golden hind tibia and high pronotal crest are diagnostic features of the older nymphs.
Observations made in 1939 revealed that most egg deposition occurred between 9 and 12 a.m. when air temperatures ranged from 80° to 90° F. At the beginning of this period they made shallow holes without depositing eggs. Later on, they selected bare ground around the edges of grass plants and dug holes into the soil depositing large clutches of eggs nearly 2 inches deep. Several males usually attended the ovipositing female. In a laboratory cage a female took 1 hour and 5 minutes from the start of drilling to withdrawal of the ovipositor. Afterward she used her hind tarsi for 1 minute to cover the aperture with soil particles and debris. In nature, a male mounts the female immediately after oviposition and mates successfully.
Egg beds occurred in various soil types, but during the 1934-40 outbreak the greatest number were found in sandy loam soil. The majority of pods were deposited in egg beds, although a few were interspersed in the extensive areas between them. In the spring survey of 1939, 187 pods were examined and found to contain an average of 65 eggs with a range of 32 to 84. The egg pod is large and slightly curved ranging from 1 to 2 inches long (Fig. 10). The eggs, 4.4 to 5.6 mm long, are pale yellow when laid but eventually turn tan.
In the Hawley site on clear days the ground temperatures rose rapidly in July and August, reaching 120° F by 10 a.m. DST. Heat induced the grasshoppers to stilt and to face directly into the sun or to face directly away from the sun. As temperatures rose further, the grasshoppers crawled onto the top of short grasses raising the body about an inch above the soil surface and away from the surrounding hot bare ground. They assumed a diagonal orientation on top the short grass facing the sun directly and shading the body.
Observed in low-density populations of less than one individual per square yard and away from egg beds, the High Plains grasshopper appears mainly quiescent-little jumping, walking, or flying unless flushed. After the basking period on 21 August 1997 from 9:20 to 11:08 a.m. DST, four appetitive flights of 15 to more than 50 feet were observed when ground temperatures ranged from 100° to 123° F and air temperatures from 77° to 85° F. Appetitive walking (pottering) was also observed on five different days. Eight observations revealed movements of 1 1/2 to 15 feet over bare ground; the grasshoppers usually broke the walk into two or three segments separated by brief pauses.
Willis, H. R. 1939. Painting for determination of grasshopper flights. J: Econ. Entomol. 32: 401-403.
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