Wireworm
Beginner
Scientific Name
Limonius spp.
Identification
Life stages: eggs, larvae, pupae, adult beetles.
Adults: Click beetles are 1–1.5 cm long with “hardshelled” brown or black bodies. The beetles snap themselves into the air, making a clicking sound, in an attempt to right themselves after being placed or falling on their backs.
Eggs: Females lay eggs in the soil
Larvae: They have elongated, nearly cylindrical bodies with three pairs of short legs just behind their heads. Mature wireworm larvae may reach a length of about 3 cm.
Pupae: They are white and inactive.
Often Confused With
Millipedes
Period of Activity
Wireworms are present all season. Wireworms have a life cycle of several years.
Scouting Notes
Field monitoring for wireworms should start early in the spring before potatoes are planted. The most direct way to detect wireworms is to walk the field while it is being ploughed or disked.
Wireworm numbers are usually highest when old fields of alfalfa, clover, or pasture are ploughed out. Wireworms can also be detected by putting a handful of bait in small nylon bags and burying the bags 6 inches deep in the soil. Carrots, wheat, corn or whole wheat flour may be used as bait. Soil temperatures need to be at least 10°C at 15 cm, so it may be necessary to cover the spot where the bag is buried with a 1.5 m x 1.5 m square of black plastic to warm the soil. Mark the site of the bag with a flag, and check the traps after 6-7 days. If baiting shows the presence of wireworms, then take soil samples to estimate the number of wireworms. Screen one square foot of soil to a depth of 15 cm at several sites in the field. If samples average one wireworm per square foot, then a control treatment is recommended.
Thresholds
See Scouting Notes.
Advanced
Scientific Name
Limonius spp.
Identification
Life stages: eggs, larvae, pupae, adult beetles.
Adults: Click beetles are 1–1.5 cm long with “hardshelled” brown or black bodies. The beetles snap themselves into the air, making a clicking sound, in an attempt to right themselves after being placed or falling on their backs.
Eggs: Females lay eggs in the soil
Larvae: They have elongated, nearly cylindrical bodies with three pairs of short legs just behind their heads. Mature wireworm larvae may reach a length of about 3 cm.
Pupae: They are white and inactive.
Often Confused With
Millipedes
Biology
Wireworms require 3 to 5 years to complete their life cycle. Female click beetles lay eggs in late spring in fields of hay, forage legumes such as red and sweet clover, or small grains. Larvae hatch in 3–7 weeks.
Most of the time is spent in the larval stage, but all stages may be present during the growing season. In cold winters, larvae move down in the soil to overwinter at depths as great as 0.6 m to avoid freezing. In the spring, larvae move up when the soil temperature reaches about 10°C. In potato fields larvae spend the growing season close to the soil surface feeding on tubers. However, if temperatures exceed 27°C in the summer and soil moisture is low, wireworm larvae move downward into cooler soil. Most damage to potato is caused by larvae in the second and third year of development. In the spring they feed on sprouts or seed tubers. Later in the growing season wireworms feed on developing tubers, producing tunnel-like holes of up to 3 cm deep that make the crop unmarketable.
Mature larvae form a pupation cell of soil particles to pupate. The adults or click beetles that develop in the fall remain in pupation cells over the winter. In spring and summer adults burrow to the surface.
Period of Activity
Wireworms are present all season. Wireworms have a life cycle of several years.
Scouting Notes
Field monitoring for wireworms should start early in the spring before potatoes are planted. The most direct way to detect wireworms is to walk the field while it is being ploughed or disked.
Wireworm numbers are usually highest when old fields of alfalfa, clover, or pasture are ploughed out. Wireworms can also be detected by putting a handful of bait in small nylon bags and burying the bags 6 inches deep in the soil. Carrots, wheat, corn or whole wheat flour may be used as bait. Soil temperatures need to be at least 10°C at 15 cm, so it may be necessary to cover the spot where the bag is buried with a 1.5 m x 1.5 m square of black plastic to warm the soil. Mark the site of the bag with a flag, and check the traps after 6-7 days. If baiting shows the presence of wireworms, then take soil samples to estimate the number of wireworms. Screen one square foot of soil to a depth of 15 cm at several sites in the field. If samples average one wireworm per square foot, then a control treatment is recommended.
Thresholds
See Scouting Notes.
Management Notes
At the present time there are no effective insecticides registered for wireworm control in Ontario.
Avoid planting potatoes in fields immediately following clover, grass, pasture, or weedy alfalfa. Summer fallow will reduce wireworm numbers by drying the soil.
In potato fields with populations of wireworms below threshold levels, do not plant grains as rotational crops. Grains tend to increase wireworm populations.
