Wireworms in Western Canada

Range: Wireworms are found across Western Canada.¹

Host crops: They can be serious pests in many crops including cereal crops, forages, corn, pulses, potatoes and other horticulture crops. Though less severe, wireworms can also feed on canola.^2,3

Biology: There are over 100 species of wireworms in Western Canada. The most economically important species are Hypnoidus bicolor and Selatosomus aeripennis destructor (prairie grain wireworm) followed by Aeolus mellilus (flat wireworm) and Limonius californicus (sugarbeet wireworm).^1,3

Preferred home: Prevalence of each species in individual fields is influenced by soil type and moisture. Hypnoidus bicolor is the most commonly found species across the geography and appears to prefer heavy soils, pasture areas, and fields recently broken from sod. Selatosomus destructor is more likely to proliferate in friable, clay and silty loam soils. Aeolus mellilus is associated with drier soils whereas Limonius californicus is more commonly found in irrigated fields. However, preferences for certain ecological conditions do not exclude specific species from other areas; it is typical to find multiple species in a single field. The extent of wireworm damage depends on the species present, population density, and larval stage. In general, larger and older larvae cause more damage.³ Heavy wireworm damage is more often associated with silty, medium textured, well-drained soils as opposed to heavy clay or very light soils; crop losses of up to 50% have been recorded.²

What does the damage look like? Wireworms damage plants by feeding on seeds and roots, and boring or shredding stems.² Stunting, wilting, and yellowing of plants could be signs of wireworm feeding. A tell-tale sign of wireworm damage is yellowing and death of the newest leaf on the seedling, but the older leaves still appear green. Ultimately, plant death from wireworm feeding can cause reduced plant population or bare patches in the field.

Wireworm damage varies from field-to-field¹ and can be patchy within a field. Wireworms move up and down within the soil according to temperature, moisture (they prefer cool, moist soil) and food source. They are attracted to carbon dioxide released from germinating seedlings. For this reason, they are most damaging when they are near the soil surface in spring. Wireworms may not move very far laterally within the field resulting in patchy feeding.²

Identification:

Wireworms are not true worms, they are beetle larvae. They are called wireworms for their wiry shape. They are slender with a jointed, hard body and have three pairs of legs behind the head. Larval length varies depending on species and life-cycle stage, with fully grown wireworms reaching approximately one to four4 centimeters in length depending on species.²

Figure 1. Wireworms.
Photo courtesy of John Gavloski, Manitoba Agriculture and Resource Development.

Similar Species

Wireworms may be confused with other insects which may be beneficial insects, of little concern, or require different management. It is important to differentiate these insects. To determine if it is a wireworm, check the legs. Wireworms have three pairs of legs behind the head. Cutworms also have three pairs of legs but unlike wireworm, cutworms have five pairs of prolegs on their abdomens (Figure 2). Stiletto flies, crane flies and seedcorn maggots may also be confused with wireworm; however, these insects have no legs. The stiletto fly preys on wireworms and is not a pest.4 Though they can be slender and wiry, centipedes can be differentiated by the many legs they have (Figure 6).

Figure 2. Dingy cutworms with leg-like structures (prolegs) on abdomen.
Photo courtesy of John Gavloski, Manitoba Agriculture and Resource Development.

Figure 3. Stiletto fly larva.
Photo courtesy of John Gavloski, Manitoba Agriculture and Resource Development.

Figure 4. Crane fly larva.
Photo courtesy of John Gavloski, Manitoba Agriculture and Resource Development.

Figure 5. Seedcorn maggot.
Photo courtesy of John Gavloski, Manitoba Agriculture and Resource Development.

Figure 6. Wireworm (left) and centipede (right).
Photo courtesy of John Gavloski, Manitoba Agriculture and Resource Development.

Life cycle

Wireworms typically live two to five years in the soil, but each species’ lifecycle differs.¹ Most of their life is spent as larvae which do the most feeding damage, especially at the later instar stages. The pupation stage lasts for about a month in mid-summer. Adult click beetles emerge from the pupa, overwinter in the soil and emerge to mate in the spring. Egg laying occurs from late May through June. Larvae hatch three to seven weeks after eggs are laid. This is the most vulnerable time in the wireworm life cycle. If wireworms do not find food within the first four weeks after hatching, they die. Those that survive typically live as larvae for multiple years feeding throughout their larval stages. Multiple generations of wireworm can be found in the same field.²

Monitoring

Scout in spring with plant stand counts, looking for thin or bare patches and damaged seedlings. Dig around these areas to look for wireworms. Bait traps can also be used to help determine if wireworms are present in the field. It is best to set these in the spring when wireworms are typically near the soil surface. There are variations between the bait traps recommended but all share the common recommendation of using a food source and a container. This could include wetted wheat or corn seed, or oatmeal balls in an onion bag or nylon stocking. Bury the traps 10 to 15 centimetres deep and mark the locations so you can return and dig them up 10 to 14 days later. Since wireworm populations can be patchy within a field, place the traps where they are most likely to be present such as areas where previous crops have had low plant stand or bare patches. Using multiple traps is also a good idea. It is important to note that wireworms may not be attracted to the bait ball if other food sources exist. This means that wireworms may be present in a field even if they are not found in the traps.

Economic threshold

This is still in development and it is probable that different thresholds will need to be established for each species. Since bait balls may not be trapping a representative sample of the field population, it may be best to start control measures if any wireworms are found.⁵

Management

Crop establishment -- promote vigorous, rapid crop growth and stand establishment by shallow seeding into warm, moist soil, with adequate soil fertility and higher seeding rates.²

Crop rotation – avoid growing multiple cereal or corn crops back to back. Flax and buckwheat are often not attacked by wireworms, and canola and pulses typically sustain much less damage. Fall seeded cereals growing vigorously in spring may outgrow wireworm feeding but could be at risk when germinating in the fall. There is much more to be understood about how crop rotation impacts wireworm damage.²

Seed treatment-- if wireworms are present then a seed treatment may be a good option for managing them.