This past winter at meetings, Iowa State University Extension entomologist Erin Hodgson heard several presentations about isopods, a new early-season soybean pest in the Midwest. Isopods are terrestrial crustaceans most closely related to lobsters and crabs. They have many common names, such as woodlice, pillbugs, sowbugs and roly-polies. Hodgson offers the following explanation and information regarding isopods.
Appearance - what does this new pest look like?
Although isopods have three major body regions (head, thorax and abdomen) like insects, it is very difficult to distinguish the regions because of the armor-like plates on the back. They have two pair of antennae (usually only one pair is obvious), seven pairs of legs and simple eyes (Figure 1). Immatures look like adults except are smaller in size and proportion. Most isopods are grey or black and some have dark markings on the back. Adults are oval in shape and three-eighths inches long. In general, the back is convex and the underside is flat or concave.
Figure 1. Isopods have become early-season pests in neighboring states.
Behavior - isopods thrive on dead and decaying crop residue
Isopods are omnivores that scavenge on dead and decaying plant or animal matter. They will also eat live, young plants such as fruit and vegetables. All life stages breathe through gills, so they must live in habitats with high humidity. No-till field crops can be attractive to isopods because they are protected under crop residue. Isopods are most active in the spring, often feeding at night. Isopods are skittish and some species curl up into a ball when disturbed (Figure 2).
Figure 2. Some isopods curl up when threatened.
Damage - more acres in no-till help promote this pest
Increasing acreage of no-till systems will encourage isopod development because high moisture is needed for survival. Some areas in Kansas and Nebraska have already experienced economically damaging levels of isopods that required replanting in soybean (Figures 3 and 4).
When scouting for other early-season soybean pests, look for clipped or missing plants. Isopods can also feed on unifoliates and scrape off leaf tissue. Managing fields for isopods is difficult because seed treatments and foliar insecticides have not proven effective. Heavily infested areas could till every other year to minimize overwintering populations and reduce soil moisture in the spring.
Figure 3. Isopods have the potential to damage emerging soybeans, especially in no-till systems. Photo by Brian McCornack, Kansas State University
Figure 4. Typical isopod damage includes clipping the cotyledon at emergence. Photo by Brian McCornack, Kansas State University