No this is not a trick question; let me explain.
What are true armyworms? True armyworms are insect pests of grasses and crops such as corn and small grains. Many of the Bt-traited corn hybrids express proteins that provide protection against the true armyworm. However, not every Bt hybrid provides protection against all insect pests. To check and see which insects your Bt traits may protect against, visit the Handy Bt Trait Table compiled by Michigan State University Field Crops Extension Entomologist Dr. Chris DiFonzo.
Additionally, not all corn produces Bt toxins – some corn producers choose to plant conventional hybrids or grow corn organically.
Susceptible corn, small grains and grass forages can sustain significant damage caused by true armyworm larvae.
Pheromone traps. True armyworm sex hormones, or pheromones, are used as bait to lure migrating moths to specially designed traps. Male adult moths looking to mate with female moths are captured in the trap when they fall in and are exposed to a plastic strip impregnated with an insecticide. Workers check traps on a regular basis looking for large moth captures (Figure). On April 27 and May 4, 63 and 85 true armyworm moths, respectively, were captured in a pheromone trap located at the Northwestern Illinois Agricultural Research and Demonstration Center in Monmouth.
During the evening, moths spend their time feeding, mating and searching for sites to lay their eggs. Large moth captures indicate that enough adult true armyworms have migrated northward to find mates and lay a lot of eggs. Eggs are laid in dense vegetation, especially grasses.
What happens 1-2 weeks after a lot true armyworms land in my pheromone trap? In a period of 1 to 2 weeks after they are laid, eggs begin to hatch. Armyworms emerge as larvae and begin feeding on host plants. It is the larval portion of the armyworm life cycle that can be most damaging to crops of economic importance.
In addition to larval emergence, systematic scouting should also begin several weeks after large trap captures, particularly in conventional or organic corn or small grains crops grown near grass pastures, near roads or along fence-rows as adults prefer to lay their eggs into dense vegetation.
For additional recommendations regarding scouting and management, visit this fact sheet produced by University of Illinois' Department of Crop Sciences Entomologists.