Wireworms and corn

Wireworm
Figure 1. Wireworm (click beetle larva). Photo: Clemson University – USDA Cooperative Extension Slide Series, Bugwood.org

Wireworms (multiple species of Coleoptera: Elateridae) the larval stage of click beetles.  

They are wormlike with an elongated body and distinct heads. They have short but visible legs and a hard textured body. The wireworm’s chewing mouthparts project forward (Figure 1). They are very active when disturbed. 

Species

Species from multiple genera can attack corn and several species occur in MN. Species of Melanotus are perhaps most commonly associated with corn damage but other species have also been cited as corn pests. They include  

  • Aeolus

  • Conoderus

  • Hemicrepidius

  • Limonius

Characteristics

Identification to the species level is difficult.

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Where they live

Click beetles are distributed worldwide, depending on the species.  Some European species have become established in North America.

Hosts

Members of the click beetle family live in many habitats. The larvae of some species are plant feeders, while some are predaceous and others may be both.

In addition to corn, wireworms are pests of wheat, potato and several other crops in agricultural environments. Wireworms are listed as pests of soybean but damage to that crop has been rare in Minnesota.

The species that attack corn are associated with grass and fields that were formerly in sod. These fields are at higher risk for damage.

Life cycle

Wireworm pest species overwinter as larvae. Research suggests that females prefer particular soil types and soil moisture regimes for egg-laying.

Although Conoderus spp. completes its life cycle in a single year, most species can have multi-year life cycles depending on food supply and climate.

Many wireworms move vertically in the soil profile and are found shallow in spring and deeper later in the season. This behavior may depend on species and in response to time season or response to soil temperature.

Pupation occurs in the soil. The adults are nocturnal plant feeders but are not pests. They are common and attracted to lights.

Natural enemies

Because they live in the soil, the natural enemies of wireworm are not well documented. Predators include certain nematode and fly larva species. They are also susceptible to fungal pathogens.

Damage symptoms

Wireworms and their feeding injury occur below ground. Corn seed is typically attacked at the embryo or germ. Injury to germinating seeds can kill plants before they emerge.

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Scouting

Wireworm can often be observed when digging in fields in early spring. However, if you find them, it does not mean that stand loss is inevitable.

If you want to sample for wireworms before planting in the spring, use bait stations buried with wheat and covered with black plastic. However, this requires considerable effort a during a short sample window and action thresholds are somewhat subjective.

Scout for damaged plants from emergence until the V5 stage. Scouting should be combined with evaluation of corn emergence, weeds and other early season corn insect pests such as cutworms, white grubs and seed corn maggot.

Managing wireworm

While economic problems generally haven’t been widespread or common, wireworm problems have been reported even less frequently in recent years. This may be due to increased use of neonicotinoid insecticides (Cruiser, Gaucho, Poncho) on corn seed or simply unfavorable environmental conditions. 

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Always read and follow the pesticide label. 

Bruce Potter, integrated pest management specialist, Southwest Research and Outreach Center 

Reviewed in 2018

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