Wireworms

True wireworm (Agrypnus sp.)

Wireworms are named for the supposed wire-like appearance of their larvae, which are shiny and cream, yellow or tan-coloured. Adult beetles are dark grey, brown or black.

There are many species of both true and false wireworms, although most are not pests. Damage is usually minor and sporadic, although wireworm species are widespread.

Eastern false wireworm (Pterohelaus sp.)

Several species of wireworms may occur in any particular crop, depending on locality, soil type, organic matter and tillage practices. False wireworm are mainly a pest in areas with heavy, black soils.

Common species include:

  • Agrypnus variabilis – sugarcane wireworm
  • Pterohelaeus spp. – eastern false wireworm, striate false wireworm
  • Gonocephalum spp. – small false wireworm, southern false wireworm, northern false wireworm.

Adults of true wireworm (Agrypnus spp.) are also known as ‘click beetles’. They are 25mm long, elongated and jump/click when disturbed. Originally inhabitants of native grasslands, they have successfully adapted to field crops and pastures.

Southern/Northern false wireworm (Gonocephalum sp.)

False wireworm adults are 10-20mm long and have flanges around the outline of the thorax. Both groups of larvae generally grow to about 30-35mm long, although Gonocephalum spp. reach about half this size. They have 3 pairs of legs close to the head. True wireworms are soft-bodied, and flatter in cross-section with a flattened head. False wireworms are hard-bodied, cylindrical and segmented with a rounded head.

Most wireworm species complete a single generation in a year, with the majority of adults emerging during spring and early summer.

True wireworm adult females can live for up to 7 weeks in the field. Eggs are about 0.5mm in diameter and slightly ovoid, and either laid singly on the soil surface or in batches of 10-15 eggs in crevices to 5cm deep. They develop through 8 larval instars over about 315 days. The final (most damaging) instar stage takes about 150 days, before pupating for about 2 weeks in the soil from October-January.

False wireworm eggs are laid singly in moist soil, usually under trash or low-growing weeds. Larvae feed on decaying vegetable matter and crop residues in the soil, as well as on newly germinated seed. Most of the larval damage to germinating crops occurs during spring, while adults are most damaging in summer.

Wireworms feed in the soil on vegetation, including roots. Crops attacked include cereals, cotton, soybeans and sunflowers. The risk period is immediately after sowing and early seedling growth, especially if germination is delayed by cold, wet weather. True wireworms can also be predatory, feeding on soil invertebrates.

  • Wireworm larvae feed on germinating seed and chew on seedling roots and shoots, resulting in patchy stands (reduced vigour or seedling death).
  • False wireworm adults chew on seedlings at or above ground level, ring-barking or completely cutting the stem.

Use germinating seed baits (GSB) or digging and sieving to detect larvae before planting. Treatment is required if more than 25 wireworm larvae are found in 20 GSB. Monitor crops after sowing until establishment.

Unlike many of the click beetle species, Agrypnus variabilis adults are not attracted to lights.

Seed dressings, in-furrow sprays and granular insecticides offer some control over larvae. For adults, use insecticide-treated cracked grain baits. Search the APVMA’s PubCRIS database for registered products.

False wireworm prefers cultivated soils to zero till. Use press wheels at sowing, set at 2-4kg per cm after planting rain or 4-8kg per cm in dry soil.

Common brown earwig is the most prevalent predator, but will not provide significant control if wireworm numbers are high.

Further information