Sweet Corn Pests - European Earwig
When earwigs feed on silks, preventing pollination.
Adult: Elongate brown body with a red-brown head; 0.5 to 0.63 inch (12.7 to 15.9 mm) long. Adult earwigs can be easily identified by a prominent pair of “pinchers” (cerci) on the rear of the body. The cerci are used for defense, catching insects, and for the males to grasp females during mating. Male cerci are strongly curved while those of the female are straighter, but curve slightly towards the tip.
Egg: Elliptical, pearly white, and 0.04 inch (1 mm diameter) long. As hatching nears, eggs darken and increase in size.
Nymphs: There are four immature or nymphal stages (instars). Nymphs are gray to light brown in color and similar in appearance to adults, but smaller.
Adults overwinter in the soil as brooding pairs or above ground in aggregations. Females lay eggs in clutches of 30-50 eggs in the spring within nests in the soil; they may lay more than one clutch if resources are sufficient. Egg hatch begins around mid-May in northern Utah. The first and some second instar nymphs remain in the nest where the mother protects them from hazards and maintains the nest by removing mold. The second through fourth instars disperse from the nest in search of food. Earwigs are active during the night (nocturnal) and hide in dark, tight, and moist places during the day. Pheromones from frass (feces) and cuticular hydrocarbons (exoskeleton chemicals) attract earwigs to congregate. There are two or more generations per year, and populations tend to build to their highest densities in mid to late summer.
European earwigs are omnivores, feeding on a diverse diet including many types of plants, fungal spores, small invertebrate animals, and decaying organic matter. They also prey on soft bodied plant pests such as aphids, scales, caterpillars, maggots and mites. The European earwig becomes a problem in corn when it feeds on the silk, preventing pollination and causing poorly developed ears that have many kernels missing on the cobs.
Sampling and monitoring programs are a critical component of making management decisions.
- Use yellow sticky cards. Hang sticky cards when potato seedlings emerge from the soil, and replace them weekly. Early in the season, place sticky cards on field edges to detect immigrating psyllids. As the season progresses, distribute sticky cards evenly throughout the field. Place at least five sticky cards per field to enhance psyllid detection.
- Visually inspect leaves for psyllid eggs and nymphs. Collect 10 mature leaves from the middle of the plant at 10 locations among the outer rows of the field. A hand lens is needed to see nymphs on the undersides of leaves and eggs on leaf edges and undersides. Note that by the time psyllids are detected in the field, if any individuals are carrying the Zebra chip bacterium, infection will likely have already occurred.
Since European earwigs can be both beneficial (eat other pest insects) and detrimental to crops, control measures should only be applied if there is unacceptable crop damage.
- Use Traps. Trapping earwigs can be an effective way to monitor and reduce earwig numbers. Some of the various types of traps that can be used include:
- Corrugated cardboard rolled and tied to stakes along borders or dispersed throughout the field.
- Rolled or crumpled moistened newspaper.
- Grooved wood placed together.
- Tuna cans, yogurt or sour cream containers (punch holes in lids). Bait containers with smelly oils such as fish or clam oil, bacon grease, and wheat bran or wheat germ and then bury the bottom of containers in the ground.
- Check traps twice per week. Transfer live earwigs into a plastic container with soapy water for disposal. If using bait, replenish as needed.
- Reduce or remove nesting and hiding places. Earwigs seek refuge in dark areas during the day. Weeds, plant debris, and volunteer corn plants should be kept clear from fields, especially in the spring.
Insecticides should be applied in the late evening just before earwigs come out to feed. Target sites where earwigs congregate (sites where females brood their young), and on plants when injury appears.
Earwigs emit a foul-smelling chemical that is distasteful to many predators; however, natural predators such as toads, song birds, chickens, ducks, and turkeys will eat earwigs. A parasitic tachinid fly will also attack the European earwig.
Image 1, Gary Alpert, Harvard University, Bugwood.org
Image 2, Gary Alpert, Harvard University, Bugwood.org