Northern Plains Integrated Pest Management GuideIPM

Authors: Buyung Hadi, Robert Wright, Janet Knodel, Phillip Glogoza, Mark Boetel, Phillip Sloderbeck, and R. Jeff Whitworth

Wireworms are the larval stage of click beetles (Coleoptera: Elateridae). Melanotus species, are among click beetles species reported from corn.

Identification

As the name implies, wireworms look wiry with conspicuous segments, anywhere between 0.23-1.5 in. (6-38 mm) and yellowish brown in color. The adult click beetles have two characteristic rear-facing pointed corners of pronotum.

Wireworms

Adult click beetles from genus Melanotus

Life Cycle and Seasonal History

Female click beetles deposit their eggs in the soil of grassy or cultivated areas. The larvae hatching from these eggs require 2-6 years to develop into adults, depending on the species. There is a generational overlap, so larvae of all instars may be found at one time. Wireworms move up near the soil line when the temperatures reaches 55˚F (12.8˚C), temperature range commonly found in spring, and move deeper into the ground when the temperatures rise above 75˚F (23.9˚C). Thus it is difficult to find wireworms near the soil surface in hot and dry conditions. Wireworms typically pupate in the soil during the fall. Pupation lasts for two weeks. The emerging adults survive the winter in the soil and surface in the following spring.

Plant Injury and Damage

Wireworms may reduce germination rate by feeding on germinating seed , damaging or eliminating a potential plant. Wireworms may also injure corn by feeding on soft stem and root tissues underground. Economic damage due to wireworms feeding in corn may occur occasionally. Wireworms often occur in clusters scattered throughout the field.

Management Approaches

Scouting and Threshold

Since the adult beetles prefer grassy environment to deposit eggs, injuries due to wireworms feeding appear to be more prevalent in corn following pasture grasses or grassland. To determine whether the wireworm population in a particular field warrant management action, soil sampling for wireworms by using bait stations should be conducted. Bait stations should be placed in the field prior to planting. A bait station consists of 2 to 3 inch (5-8 cm) deep hole with one cup of untreated wheat or shelled corn in it. Soaking seed for 24 hours is recommended. Cover the grain with soil and then an 18-inch2 (46 cm 2) piece of black plastic to increase soil temperature and seed germination. Baits should be placed in grassy areas in the field or parts of the field with a wireworm history. Mark the site of the baits with surveyor flag to assist later finding. Use 5-10 bait stations per 30 acre. The baits can be checked for wireworms after two weeks. The economic threshold is an average of 1 wireworm per bait station for the whole field. If this population level is reached, soybean seed treatment against wireworm is recommended. In areas with cold spring like North Dakota, baiting can be conducted in the fall. Spring baiting in these areas may fail to estimate true population of wireworms due to cold soil temperature and reduced wireworm activity.