TWO-STRIPED GRASSHOPPER ( Orthoptera ) TAXIDERMY
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Phylum Arthropoda (Arthropods)
Subphylum Hexapoda (Hexapods)
Class Insecta (Insects)
Order Orthoptera (Grasshoppers, Crickets, Katydids)
Suborder Caelifera (Grasshoppers)
Family Acrididae (Short-horned Grasshoppers)
Subfamily Melanoplinae (Spur-throated Grasshoppers)
Species bivittatus (Two-Striped Grasshopper)
TWO-STRIPED GRASSHOPPER There are 18,000 kinds of grasshoppers in the world. All species of grasshoppers share the common characteristic of being a long, slender insect and is known for its strong mandibles, or jaws, which are adapted for chewing. The grasshopper has two pairs of wings. The front pair is rigid, while the hind pair is larger, membranous and often brightly coloured. These wings help some species fly well, yet others fly poorly or not at all. It also has three pairs of legs, all of which are used for walking. The back pair is more muscular and used for jumping or initiating flight. There are two main groups of grasshoppers: long-horned and short-horned, determined by the length of antennae. The two-striped grasshopper, a short-horned grasshopper, is recognized by the stripes on its back, the colours varying due to location and maturity. The grasshopper has no ears. Instead it uses organs called tympana to hear, circular membranes found in the abdomen of the insect where the hind legs attach to the body. It also has five eyes. The two large eyes are on either side of the grasshopper's head, each with thousands of single lenses, allowing it to see in all directions. The three smaller eyes one at the base of each antenna and one between the two antennae are single eyes and it is unknown what their purpose is.
Two-striped grasshoppers feed on grasses and broad-leaved plants. The broad-leaved plants are necessary for maximum growth. They prefer the lush growth around edges of streams, marshes and cultivated fields. Hosts include weeds and most crops, especially alfalfa and vegetables, and occasionally trees and shrubs. They were first noted in large numbers in 1932 after broad-leaved weeds became common on the Prairies.
This species overwinters in the egg stage. Drift ridges of soil in abandoned fields that suffered severe wind erosion are favored egg laying sites. Other areas include heavier textured soils along roadsides, closely cropped pastures, fence rows, ditch banks, prairie sod and field margins, but not cropped fields.
Air temperature must be above 20'C and soil moisture between 10 and 20 per cent for egg deposition to occur. Forty to 100 eggs are laid per pod; only two or three pods are laid by each female during August and September.
First instar nymphs appear in late May to early June.
Number of generations
There is one generation per year.
Natural enemiesThe two-striped grasshopper has a greater number of natural enemies of the egg stage than have the clear-winged or migratory grasshoppers. The nymphs and adults are attacked by at least twelve species of insect parasites, two mermithid nematode species, three microbial pathogens and by various birds, small mammals and parasitic mites. Insect parasites are most abundant two or three years after an outbreak. There are various records of heavy mortality from fungus disease to which the two-striped grasshopper seems particularly susceptible. Red mites have infested up to 100 per cent of a population; however, about eight per cent is a more normal figure. Their effect on these grasshoppers is unknown.
Effects of weather
Population size is primarily determined by weather. Outbreaks are usually preceded by two to three years with hot, dry summers and open falls. Dry weather increases the probability of egg survival, hastens spring hatch, and promotes nymphal development and adult feeding. Open falls allow grasshoppers more time to feed and lay eggs. Cool, wet weather increases egg mortality by promoting fungal diseases, retards nymphal development, reduces the numbers of eggs laid by delaying sexual maturity and reduces the activity of grasshoppers at all stages.