Northern Plains Integrated Pest Management GuideIPM

Author: Frank B. Peairs[1], Buyung Hadi, Gary Hein, John Campbell, Janet Knodel, Phillip Glogoza, Mark Boetel, Jeff Whitworth, Holly Davis, Phillip E. Sloderbeck and J.P. Michaud.

Identification

There are many different species of grasshoppers, with some having a greater pest potential than others. Correctly identifying a species is important because (1) species vary in their biotic potential and in their capacity for causing damage; (2) depending on their food habits, species may be either pests or beneficials; (3) certain species of pest grasshoppers are highly migratory and often pose a serious threat to distant crops; (4) species vary in their seasonal cycle (period of hatching, development, and reproduction) which in turn affects the timing of control treatments; (5) because current chemical and biological methods of controlling grasshoppers are more sophisticated, their effective use requires greater knowledge of the pests' life histories and habits; (6) as environmental impacts of control are better known, identification of species is important in the selection of management strategies. Common pestiferous grasshopper species include: differential grasshopper, Melanoplus differentialis; redlegged grasshopper, Melanoplus femurrubrum; migratory grasshopper, Melanoplus sanguinipes, and twostriped grasshopper, Melanoplus bivitattus.

Eggs of redlegged and differential grasshoppers are laid in cemented clusters (egg pods) approximately 0.5-2 inches (1-5 cm) below the soil surface. A cluster of redlegged grasshopper eggs may contain 25-30 individual eggs while a cluster of differential grasshopper contains 50-150 individual eggs.

Grasshopper nymphs resemble the adults, but are smaller in size and have incompletely formed wings. The nymphs of redlegged grasshoppers feature a broad, pale-colored stripe running on the side of the head, beginning around the gena ("cheek" area) and crossing the thorax to the side of the first segments of the abdomen. The nymphs of differential grasshopper usually have the broad, pale-colored band running on the side of the thorax but not continuously crossing the side of the head.

A redlegged grasshopper nymph, notice the pale-colored band continuously crossing the side of head and thorax

Redlegged grasshopper adults are 0.86-1.25 in. (22-32 mm) long with a reddish brown upper surface, a bright yellow underside and characteristic red color on the lower part of the hind legs. The adults of differential grasshopper are 1.1-1.73 in. (28-44 mm) long with yellowish brown bodies and distinct v-shaped black markings on the upper part of the hind legs. The adults of migratory grasshopper are between 0.9-1.0 in. (22-25 mm) long, tan or gray in color with a black band extending from behind the eyes across 2/3 of the side of pronotum (the chest area). The lower part of the migratory grasshoppers' hind legs usually have bluish-green or reddish color. The adults of twostriped grasshopper are 1.1-1.5 in. (28-38 mm) long, tan colored with two light yellow stripes across the top of the head, pronotum and the base of forewings.

An adult redlegged grasshopper, notice the red color on the lower part of the hind leg and yellow underside

An adult differential grasshopper, notice distinct v-shaped markings on the upper part of the hind legs

An adult migratory grasshopper, notice the black band extending behind the eyes across 2/3 of the side of pronotum

An adult twostriped grasshopper, notice the light yellow stripes along the top of the head, pronotum and forewings

Life cycle

Most grasshoppers overwinter as eggs in the form of a pod laid in the soil. These elongate-shaped pods may contain from 20 to 120 eggs each. Egg pods are commonly deposited in the soil, on undisturbed areas such as grasslands, pastures, ditches and field borders. The timing of egg hatch is strongly influenced by spring temperature with warm spring inducing early hatching and by grasshopper species. Eggs of the primary grasshopper pest species hatch into nymphs in late May and June, maturing in two to three months. Small nymphs feed on nearby foliage; as nymphs develop and grow they disperse more widely; feeding during the day and resting during the afternoon and night on vegetation. Because of limited fat reserve, nymphs are vulnerable to adverse weather. Extended cool temperatures (below 65˚F [below 18.3˚C]) and rainy weather immediately after hatching can increase nymphal mortality.

By August most nymphs have matured to the adult stage, the only stage with well-developed wings, and can readily move out of hatching area into croplands. Adult grasshoppers begin to lay eggs one to three weeks after reaching adulthood. Grasshopper outbreaks are more commonly associated with lower spring rainfall and damage is more likely in areas with less annual rainfall or during drought years when grasshoppers are more likely to move into cropland.

The USDA-ARS' Grasshoppers website provides a comprehensive source of information on grasshopper biology, ecology, identification and management of grasshoppers and crickets in North America.

Plant Response and Damage

Grasshoppers can be a pest to many crops. There are many species of grasshoppers, but only a few species actually have pest potential. Most of the grasshopper damage on corn is caused by four species described above. On corn, grasshoppers will attack leaves, tasels, green silks and ears. Often grasshopper populations develop in uncultivated areas and move into cultivated fields, thus the infestation moves from field margin inward.

Management

Monitoring, Scouting and Threshold

Hazard Maps are developed each year as a cooperative effort of USDA-APHIS-PPQ and are available at the following site: USDA-ARS' Grasshoppers website

Around cropland, grasshoppers eggs are often laid outside the field, moving in as the crops progress and grasshoppers mobility increases. Thus, field margins should be monitored for hatching nymphs in spring and early summer. To monitor field borders, randomly select 18 sites on the field border; on each site visualize one square-foot area and count the number of grasshopper nymphs within the area or that move from the area as you approach. When first learning this method, it may be useful to practice with a flag-delineated square-foot area to improve one's ability to visualize a square-foot area. After counting the number of nymphs on all 18 sites, divide the number of total nymphs by two to get the estimate of nymph count per square yard (9 square feet). If the estimated count of grasshopper nymphs per square yard is equal to or higher than the threatening level given in Table 1, control maybe considered. Grasshopper control is most effective before the insects become large nymphs or adults, as these stages are more mobile and more difficult to control.

Table 1. Treatment thresholds for immature and adult grasshoppers (from University Minnesota)

Rating	Immatures/yd2		Adults/yd2
	Margin	Field	Margin	Field
Light	25-35	15-25	10-20	3-7
Threatening	50-75	30-45	21-40	8-14
Severe	100-150	60-90	41-80	15-28
Very Severe	200+	120+	80+	29+