Wireworm

Wireworms are the larvae of click beetles (family Elateridae). There are numerous species of wireworms, each with its specific host plants, but many species share common traits and behaviors.

Host Plants

Wireworms have a broad host range and can feed on a variety of plants. They are particularly problematic in vegetable crops such as beans, beets, cabbage, carrots, lettuce, onion, peas, potatoes, radishes, and corn but can also affect cereal crops like wheat and barley, and herbaceous ornamentals. They are known to feed on the roots of several other plants as well, including numerous grasses and weeds.

Regions impacted

Wireworms are a global pest found in numerous countries worldwide. They can be particularly problematic in regions with high soil moisture and organic matter, such as those used for irrigated crop production.

Description

Wireworms are named for their wire-like appearance. They are slender, elongated, and segmented, typically measuring between 0.5 and 1.5 inches long, depending on the species and stage of development. The color varies but is usually tan, brown, or yellow. Their hard exoskeletons and cylindrical bodies give them a somewhat jointed, wire-like look. Adult beetles are usually brown or black and have a characteristic clicking mechanism that allows them to jump when they are placed on their backs.

Life Cycle

Wireworms, the larval stage of click beetles, have a life cycle that involves four distinct stages: egg, larva, pupa, and adult. However, the time spent in each stage can vary significantly depending on the species and environmental conditions.

• Egg Stage Adult female click beetles lay their eggs in the soil during spring and summer, usually in grassy areas or fields. The eggs are small, round, and white, and are often laid in clusters. Depending on the species and weather conditions, eggs can hatch in a few weeks.
• Larval Stage Once the eggs hatch, the larvae (known as wireworms) burrow into the soil and begin to feed on plant roots, seeds, and tubers.
  This larval stage is the longest and most destructive phase of the life cycle. Depending on the species and environmental conditions, wireworms can remain in the larval stage for anywhere from 2 to 6 years. They continue feeding and growing throughout this period, passing through several larval instars (growth stages) before they pupate.
  During this time, wireworms can overwinter in the soil, going deeper during cold weather and moving closer to the surface during warmer conditions. They can survive cold winters and periods of low food availability by going into a state of dormancy.
• Pupal Stage When wireworms are fully grown, they enter the pupal stage. This usually occurs deeper in the soil. During this stage, the wireworms transform into adult beetles. The pupal stage typically lasts several weeks and occurs during the spring or early summer.
• Adult Stage (Click Beetle) Adult click beetles emerge from the soil after pupation. Adult beetles feed on plant foliage but are not typically considered significant pests compared to the larval stage.

After emergence, the adult beetles mate and the females lay their eggs to begin the next generation. The adults typically live for a few weeks to a few months, during which time they can lay several hundreds of eggs. After laying their eggs, the adult beetles die, completing the life cycle.

Because of the wireworm’s long life cycle, particularly the prolonged larval stage, populations can persist in the soil for many years, causing ongoing damage to susceptible crops. Hence, understanding their life cycle is crucial for effective pest management.

Damage and Detection

Wireworms can cause significant damage to crops and garden plants. Detecting their presence early is essential for effective control and prevention measures.

Damage

Wireworms can cause significant damage to a variety of crops due to their feeding habits. They feed on seeds, roots, tubers, and other underground parts of plants, making them particularly destructive to root crops like potatoes, carrots, and onions, as well as grain crops like corn and wheat.

The larvae bore into stems and roots, often leaving small, round holes and tunnels. This not only weakens or kills individual plants but also opens the way for secondary infections as the damaged plants are more susceptible to diseases and other pests.

In potatoes and other tuber crops, wireworm damage is often seen as small, shallow holes on the surface or deeper, tunnel-like holes, which can make the crop unmarketable. For seedlings and young plants, wireworm damage can result in wilting, yellowing, stunting, or death if the damage is severe enough.

Detection

Detecting wireworms can be a challenge due to their subterranean lifestyle. However, a few signs can indicate their presence:

• Unexplained plant damage: If plants in your field or garden are wilting, yellowing, or dying without a clear reason, it could be due to wireworms. Look for damage to the roots or lower stems.
• Holes in tubers or roots: Wireworms leave characteristic small, round holes in tubers and roots. These holes often appear shrunken or sunken as the plant material around them dies.
• Poor germination or thin stands: If you notice poor germination rates or unusually thin stands of plants, it could be because wireworms are eating the seeds or seedlings.

To confirm the presence of wireworms, you can dig in the soil around affected plants and look for the larvae. Another method involves placing bait stations, consisting of pieces of potato or carrot, in the soil. Wireworms are attracted to these baits and can be found feeding on them after a few days.

Regular soil sampling and monitoring are important for early detection of wireworms. If you have a history of wireworm problems in your field or garden, it’s particularly important to monitor for their presence.

Prevention and Control

Prevention

Preventing wireworms can be challenging due to their lifecycle and the length of time they spend in the soil. However, there are several strategies you can employ:

• Crop Rotation: Regular rotation of crops can disrupt the lifecycle of wireworms, reducing their populations over time. Crop rotations should include non-host plants, such as certain legumes and grasses, which are less preferred by wireworms.
• Field sanitation: Plowing and harvesting as soon as crops are mature can expose wireworms to predators and reduce their food sources, limiting their population growth.
• Late planting: Avoid planting too early in cold soils. Opt for later planting when soils are warmer, as it speeds up germination, helps plants establish quickly, and minimizes the time they are vulnerable to wireworm damage during early growth stages.
• Monitoring and trapping: Regularly monitor fields for signs of wireworm damage and consider using bait stations to trap and monitor wireworm populations. This can help you catch infestations early before they cause significant damage.

Control

There are a few options for controlling wireworms once they’re present in your fields:

• Chemical controls: Insecticides can be applied to the soil to kill wireworms. However, because wireworms live in the soil, these treatments may not always be effective, and they can have negative environmental impacts. Therefore, it’s important to use them judiciously and in combination with other control methods.
• Biological controls: There are a few natural enemies of wireworms, including certain species of beetles, nematodes, and fungi, which can help to control their populations. These can be introduced into fields as part of an integrated pest management strategy.
• Resistant varieties: Some plant varieties are more resistant to wireworm damage than others. If wireworms are a significant problem in your area, consider planting resistant varieties.
• Use of trap crops: Planting a preferred food source for wireworms, like potatoes, in a concentrated area can draw them away from the main crop. After they’ve congregated, the trap crop can be treated with an insecticide to kill the wireworms.
• Cultivation practices: Practices such as deep plowing and summer fallowing can expose wireworms to the surface, where they can be preyed upon by birds and other predators.

Remember that prevention and control measures are more effective when used in combination. The goal should be to manage wireworm populations to minimize crop damage rather than trying to completely eliminate them, which is often not feasible. A well-implemented integrated pest management (IPM) strategy is the best approach for dealing with wireworms.