Issue No. 10, Article 4/June 2, 2006
One for the Record: Springtails and Crickets Ravage Soybean Field?
Before the Memorial Day weekend, Dave Feltes, Extension IPM educator at the Quad Cities Extension Center, visited a soybean field that was being "destroyed by some sort of insect." Dave, a diagnostic veteran, visited the 200-acre field in Henderson County and reported back that he had never seen anything quite like it before. We tried to help diagnose the problem over the telephone from comments such as "there were a gazillion of these tiny insects" and "the ground looked like it was moving." The latter comment prompted us to think the culprits might be false chinch bugs, but the scenario was not quite right. The field of soybeans had been drilled into corn stubble in sandy soil, and weeds were not evident. The grower wanted to know what he was dealing with before replanting the field. Something--or more than one something, as it turned out--was eating holes in the cotyledons. The damage to the seedlings was so extensive that replanting was warranted.
Insect injury to cotyledons in a soybean field in Henderson County, Illinois, May 2006 (photo courtesy of Dave Feltes, University of Illinois Extension).
Dave took some photographs of the insects and discovered even before we had seen the photos that the most numerous insects he observed were springtails--primitive, wingless insects in the order Collembola. But he also found other insects in the collection, which we ultimately determined were very small crickets.
Crickets have been known to cause significant injury to soybeans on relatively rare occasions, although the ones that have caused injury in the past were considerably larger than those Dave collected. Nonetheless, with their chewing mouthparts, crickets can cause injury resembling injury from grasshoppers, a close relative. In the Henderson County field, the crickets were numerous and the soybean seedlings were small.
Cricket nymph found in a soybean field in Henderson County, Illinois, May 2006 (photo courtesy of Dave Feltes, University of Illinois Extension).
Springtails, on the other hand, are not usually considered to be pests of field crops. Springtails are soil-dwelling arthropods that feed primarily as scavengers on decaying vegetation and soil fungi; they are decomposers. In addition, springtails are most common in moist, humid, cool environments. Although the corn residue in the Henderson County field must have provided appropriate habitat, the field would not be characterized as moist, humid, or cool.
A quick review of some older literature and information on the Web revealed that some species of Collembola feed on living plants, such as house plants, greenhouse plants, or cultivated mushrooms. One species, the globular-shaped garden springtail (Bourletiella hortensis), feeds on seedling plants. Chris DiFonzo, extension entomologist at Michigan State University, wrote about globular-shaped springtails feeding on soybean cotyledons in issue no. 7 (May 25, 2006) of their Field Crop Advisory Team Alert Newsletter. However, the springtails Dave Feltes collected were not garden springtails but elongate ones (body form entomobryomorphid [keep that in your glossary]).
Elongate springtail found in a soybean field in Henderson County, Illinois, May 2006 (photo courtesy of Dave Feltes, University of Illinois Extension).
The common name "springtail" derives from the forked structure, called a furculum, on the underside and rear of the abdomen. This structure is snapped against the surface of a substrate to enable the springtail to "spring" or "hop" to escape predation. Springtails are very small (1 to 5 mm) and occur in a variety of shapes and colors. They can be found in a large variety of habitats throughout the world, including forest floors, beaches, glacial ice, tropical treetops, surface of freshwater lakes and ponds, and grasslands. From a Web site at the University of Missouri, we learned that many elongate species of springtails are surface dwellers, with traits (e.g., hairs) that allow them to tolerate variable environments and prevent them from desiccation (drying out).
We have no explanation for the occurrence of such large numbers of springtails and crickets in that particular soybean field. It is likely that the habitat of the field last year was appropriate for both types of insects and that the corn residue this year has provided shelter. Although this situation is an oddity, it demonstrates that skills in insect identification and diagnosis of insect injury to crops are essential for making pest-control decisions. This situation may not occur again any time soon, or maybe it will become more commonplace, as Chris DiFonzo indicated is happening with sugar beets in Michigan. Whatever the case may be, keep your eyes open for virtually anything when scouting field crops.--Kevin Steffey and Mike Gray