May 26, 2010

Based on the number of eggs laid last year, the potential for abundant grasshoppers is high this year (see CropWatch article, Western Nebraska Rangeland at High Risk for Grasshopper); however, the weather and beneficial insects may be working against them. Currently, the first group of rangeland grasshoppers has hatched and you may now notice 1st and 2nd instar nymphs in grasslands. So far the infestation has been light; however, peak hatch has not yet occurred.

Figure 1. The bee fly is a beneficial insect. The larvae of some bee fly species parasitize grasshopper eggs. (Photo by J. Kalisch)

Since April 9, western Nebraska has experienced above normal rainfall and below normal temperatures. In the past 30 days in western Nebraska average temperatures have been 3 to 8 degrees Fahrenheit below normal while rainfall has been 50% to 140% of normal. For some areas of western Nebraska, these cool, wet conditions should result in a healthy rangeland with fewer grasshoppers.

In addition to the weather, many beneficial organisms can reduce grasshopper abundance. Beneficials range from bacteria to birds to numerous beneficial insects. One of the many organisms that can attack grasshoppers is the bee fly (Figure 1). Bee flies superficially look like bees, but are actually classified in the family Bombilyiidae (a family of flies). Little information is known about bee flies, except that the adults will feed on nectar and the larvae of some species parasitize grasshopper eggs. In fact, 13 genera of bee fly are known to parasitize grasshopper eggs.

This past week, an employee of the Western Cooperative Company (Gering, Nebraska) brought an insect larva into my lab for identification. It was a bee fly larvae,  one of many found in a newly planted corn field near a grassy pasture. The grower apparently had come across a grasshopper egg bed that had been heavily infested with these beneficial insects. Few entomologists have seen bee fly larvae. In fact, many larvae have yet to be associated with their adult form and many species' life cycles are unknown.

If weather conditions remain favorable for these and other beneficial organisms, grasshoppers may have less impact than originally expected in grasslands. 

Jeff Bradshaw
Extension Entomologist, Panhandle REC, Scottsbluff
Jim Schild
Extension Educator in Scotts Bluff County