No. 14/June 25, 1998
Grasshopper Nymphs Are Out and About
Robert Bellm, Extension crop systems educator in Edwardsville, reported finding numerous grasshopper nymphs in southern Illinois recently, and his note reminded me that I had seen a few grasshopper nymphs a couple of weeks ago in Champaign County. As you continue to scout fields for key insect pests like corn rootworms and corn borers in corn and bean leaf beetles in soybeans, add grasshoppers to your list of pests to keep an eye on.
The two most common species of grasshoppers in Illinois are the differential and redlegged grasshoppers. They have similar life cycles. Females lay eggs in the soil by forming burrows with their abdomens. They deposit clusters of eggs 0.5 to 2 inches below the soil surface, then secrete a frothy covering over the eggs; soil particles adhere to the frothy secretion. The secretion hardens, forming a soil-covered egg pod about 1-inch long. The number of eggs in each pod varies from less than 10 to more than 100. A single female deposits an average of 200 to 300 eggs in her lifetime. Most species deposit eggs in uncultivated fields, roadsides, and pastures. These areas are called "egg beds," and the numbers of eggs in the egg beds are extremely large during outbreak years.
Egg hatch can begin in late April but may be as late as early July. June is usually the month when grasshoppers begin to emerge from their overwintering quarters in Illinois. A warm spring after a warm fall favors early hatching; a cool fall and spring delay egg hatch.
Both differential and redlegged grasshoppers have five (occasionally six) instars. The first instar is very small, about 1/8 inch. With adequate food and warm, dry weather, nymphal development requires 35 to 50 days. Both species complete one generation per year.
Most people associate grasshoppers with hot, dry weather. In general, that association is true. Weather regulates both the size of grasshopper populations and the effect they have on the crop. Temperatures during the previous summer can influence the current season's grasshopper population. A large number of warm, sunny days from late June through September allows grasshoppers to develop quickly, thus allowing females to deposit large numbers of eggs. Conversely, numerous cool days through the same time period result in fewer eggs being deposited. Extreme, prolonged drought causes eggs to desiccate or stops egg development. Wet weather in the late spring and summer also may promote establishment and development of a fungal disease organism that can suppress grasshopper populations. Consequently, the weather thus far this year suggests that grasshoppers may not be problematic in Illinois. However, as the season continues, especially if the weather becomes hot and dry, we will need to remain watchful of grasshoppers in our crops.
Kevin Steffey (firstname.lastname@example.org), Extension Entomology, (217)333-6652