As addressed in previous grasshopper articles, the chances of high grasshopper pest numbers in range and cropland is high for 2021. As you consider control methods like contact or systemic insecticides, please consider biological control as part of your Integrated Pest Management (IPM) plan.
The naturally occurring protozoan Nosema locustae such as Semasphore effects grasshopper populations. The organism is generally mixed with bait. A grasshopper becomes infected if it ingests the bait, infected vegetation or an already diseased grasshopper. A grasshopper population infected with this organism may be reduced from 5 to 40 percent in one year (Calpas, 2003). Infection can lead to death but more often causes reduced vigor and decreases egg-laying activity. Semasphore has been shown, in some cases, to cause a small reduction in grasshopper populations after several weeks, but it is not a good choice when immediate control is necessary.
Biological control is an important component of an (IPM) program. The four most important egg predators are bee flies, blister beetles, ground beetles and crickets. The common field cricket, feeds directly on grasshopper eggs, and may consume up to 50%. (Calpas, 2003) Bee flies and blister beetles deposit their eggs in the soil near grasshopper eggs. When the larvae of egg predators hatch, larvae locate the egg pods and feed directly upon eggs destroying up to 80 percent (Calpas, 2003). An egg parasite from the genus Scelio deposits its eggs within the newly-laid grasshopper eggs. Scelio complete development within the egg and emerge in time to parasitize the eggs of the next generation of grasshoppers. Egg parasites may destroy from 5 to 40 percent of eggs (Calpas, 2003). Spiders, robber flies, some wasps and many birds consume large populations of grasshoppers. Common names include flesh flies, robber flies, muscoid flies, tangled vein flies, threadworms, fungi, micro-sporidians and many numerous
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others. The fly maggot feeds inside the grasshopper and eventually kills the host as it leaves the body. Cumulative parasitism on grasshoppers can range up to 60 percent (Calpas, 2003).
A naturally occurring fungus Entomophaga grylii can be effective in controlling grasshoppers under warm, humid conditions, and may occasionally reach epidemic proportions. The disease leaves the corpses of its victims clinging to the stems of plants with their heads pointing upward (Calpas, 2003). Grasshoppers become infected from spores which stick to the bodies as they seek food. These spores germinate and penetrate the insect cuticle. The fungus multiplies in the blood and grows on internal organs. E. grylii is capable of causing high mortality in grasshopper populations.
Literature Cited
Calpas J. Johnson D. 2003. Grasshopper management. Agrifacts, Agdex 622-27.
Montana State University, U.S. Department of Agriculture and Montana Counties Cooperating. MSU Extension is an equal opportunity/affirmative action provider of educational outreach.
