• July 22, 2014

Dry weather increases grasshopper survival

Large outbreaks of bugs means more damage to landscape

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Posted: Saturday, July 20, 2013 4:30 am

Grasshoppers are among the most widespread and damaging pests in Texas. There are about 150 species of grasshoppers in the state, but 90 percent of the damage to crops, gardens, trees and shrubs is caused by just five species:

  • Differential grasshopper
  • Red-legged grasshopper
  • Migratory grasshopper
  • Two-striped grasshopper
  • Packard grasshopper

Grasshoppers cause some damage every year, but they become very destructive during outbreaks. The main factor affecting grasshopper populations is weather. Outbreaks, or exceptionally large populations, are usually preceded by several years of hot, dry summers and warm autumns. Dry weather increases the survival of nymphs and adults. Warm autumns allow grasshoppers more time to feed and lay eggs. Grasshoppers have a high reproductive capacity. The female lays an average of 200 eggs per season, and sometimes as many as 400 eggs. If favorable weather increases the number of eggs, nymphs and adults that survive, the grasshopper population may be dramatically larger the following years.

Biology: Grasshoppers deposit their eggs ½ to 2 inches below the soil surface in pod-like structures. Each egg pod consists of 20 to 120 elongated eggs cemented together. The whole mass is somewhat egg-shaped. Egg pods are very resistant to moisture and cold and easily survive the winter if the soil is not disturbed. Grasshoppers deposit eggs in fallow fields, ditches, fencerows, shelter belts and other weedy areas, as well as in crop fields, hay fields and alfalfa.

Eggs begin hatching in late April or early May. Hatching peaks about mid-June and usually ends by late June. If spring weather is cool and extremely dry, hatching may be delayed and continue into July.

Young grasshoppers are called nymphs. They look like adults, but are smaller and have wing pads instead of wings. Nymphs go through five or six developmental stages and become adults in 40 to 60 days, depending on weather and food supplies.

The adults of grasshopper species that damage crops become numerous in mid-July and deposit eggs from late July through fall. Usually only one generation of grasshoppers is produced each year.

Biological control: Grasshoppers have many natural enemies that help control their populations. A fungus, Entomophthoragrylli, often kills many grasshoppers when the weather is warm and humid. Infected grasshoppers strike a characteristic pose at the top of a plant or other object. The grasshopper grasps the plant in a death embrace with the front and middle legs, while the hind legs are extended. It dies in this position. Fungal spores develop in and on the grasshopper’s body, then become airborne and infect other grasshoppers.

Another natural enemy is protozoan, Nosema locustae. Its spores have been incorporated with bran to make insecticide baits. Baits kill some nymphs but almost no adults, though infected adults lay fewer eggs. Baits act too slowly and kill too few grasshoppers to be useful for immediate control.

Other natural enemies include nematodes called hairworms and insects that feed on grasshoppers, such as the larvae of blister beetles, bee flies, robber flies, ground beetles, flesh flies and tangle-veined flies. Birds (quail, turkey, larks, etc.) and mammals also eat grasshoppers, but have little effect on large populations.

Mechanical control: One way to control grasshopper populations is to eliminate sites where they might deposit eggs. Grasshoppers prefer undisturbed areas for egg laying, so tilling cropland in mid- to late summer discourages females.

Cultural control: Controlling summer weeds in fallow fields has two benefits:

If grasshopper eggs are already in the field, there will be nothing for nymphs to feed on when the eggs hatch.

Fields will not be attractive to egg-laying adults because there is nothing on which to feed.

Also eliminate tall grass and weeds from around any plants you wish to protect (crops, trees and gardens). This makes the area less attractive to grasshoppers and makes it easier for birds to prey on grasshoppers.

Monitoring populations: Farmers and ranchers should start watching for grasshoppers early in the season and begin control measures while grasshoppers are still nymphs and still within the hatching sites (roadsides, fencerows, etc.). Treating grasshoppers early means 1) having to treat fewer acres and use less insecticide, 2) killing grasshoppers before they cause extensive crop damage, and 3) killing grasshoppers before they can fly, migrate and lay eggs. Also, smaller grasshoppers are more susceptible to insecticides than larger ones.

Chemical control: There are several options for grasshopper control on rangeland and cropland. The biological work well as do the conventional insecticides. Control should be considered in the early season (now) to control and prevent spread. Often times cropland is invaded from the edge of fields inward. Treating a barrier around the perimeter (100 feet or more) will protect the entire field.

A complete publication is available at the County Extension Office at 1605 N. Main, Belton, Texas. You may also call (254) 933-5305 or email l-zoeller@tamu.edu.

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