Correct Identification of Potential Insect Pests: A Key First Step in Pest Management

May 7, 1999
While monitoring fields for black cutworms, it is quite likely that you will observe many other life forms in addition to cutworms. One nontarget organism you may find is the millipede; you've probably spotted these so-called "thousand leggers" in your basements and in pots of house plants as well. Millipedes (Figure 1) are distant relatives of insects and primarily serve as scavengers of decaying plant materials. The majority of millipedes have 30 or more pairs of legs, with each body segment bearing two pairs. Millipedes are not capable of cutting plants and should not be considered pests of corn.

Other creatures encountered while scouting for cutworms might include ground beetle larvae and crane fly maggots (Figure 1). Dave Feltes, IPM Educator, Quad Cities Extension Center, recently reported that a cornfield suspected of having an infestation of black cutworms was instead supporting a thriving population of crane fly maggots. With a little knowledge of what crane fly maggots look like, producers can save themselves the expense of an unnecessary insecticide treatment. Crane fly maggots are commonly misidentified as cutworms, but these large maggots are not pests and should not be considered of economic importance. They feed on organic matter in the soil and are most often found in fields that are poorly drained. The maggots are legless, have poorly developed heads, and vary in length from 0.7 to 1 inch when fully grown, depending on the species. Ground beetle larvae are alligator shaped and are armed with impressive and hardened mouth parts, which they use to capture and feed on prey. In some cases, ground beetle larvae are confused with wireworms; immature ground beetles can usually be separated from wireworms by examining the rear portion of the abdomen: Many species of ground beetle grubs have two prolonged structures that extend from the tip of their abdomen, whereas wireworms have hardened tail-plate regions that are sometimes notched or somewhat pointed.

Before you decide that a rescue treatment is required for black cutworm control, be absolutely sure that the target insect has been identified correctly. Each year we receive several reports that fields have been treated needlessly.--Mike Gray

Author: Mike Gray