Which false wireworm?

False wireworm is a catch-all name for several pests that can impact broadacre crops.

 

At cesar we receive many identification requests for insects that are suspected to be ‘false wireworm’, which is a common term used to refer to several pest species in the Tenebrionidae beetle family. As larvae, they have cylindrical, hard bodies with three sets of legs located behind the head. They can often be distinguished from other beetle groups by a pair of spines at at their tail-end. Common species of true wireworm larvae, which are from a different beetle family entirely (Elateridae), also have similar upturned tail spines, but these protude from a plate-like structure not present in false wireworm larvae. Tip: Use a magnifying lens on your phone camera or a hand lens to view these structures.

Three common groups of false wireworm have been observed impacting broadacre crops in Victoria and southern NSW this season.

 

Bronzed field beetle (Adelium brevicorne)

Bronzed field beetle adults damage canola plants by chewing on seedlings at or above ground level. Larvae can feed on roots and underground stems of plants, however, they may also be present in the soil and cause little or no damage to plant seedlings. This is because they primarily feed on dead organic matter and high numbers are required to cause serious crop damage. When numbers are high, larvae can cause significant damage to canola. Plant stems become weak and seedlings often die, causing bare areas or thinning within a crop. Damage is most severe where crop growth is slowed by dry or cool conditions.

Recently, high densities of bronzed field beetle adults have been identified in a 600 acre of 4-leaf canola north of Lockhart in the NSW Riverina. Large patches of the canola have been damaged and control has been necessary. Large numbers of millipedes were also present in the paddock, however these were identified as a non-pest species of polydesmid millipede (likely Akamptogonus novarae), and are very unlikely to have contributed to the damage.

If bronzed field beetle are suspected in your paddock, be sure to inspect the soil and canola roots for the larval stage as both adults and juvenile stages can occur concurrently at this time of the year.

 

Bronzed field beetle adults and larvae can occur concurrently (Source: Chris Dunn).

For more information refer to our Bronzed field beetle Pest Note.

 

Vegetable beetle or southern false wireworm (Gonocephulum spp.)

Vegetable beetle can be a pest as larvae and adults. The adults are 6-10 mm long (adult vegetable weevils are a similar size, but are not to be confused – they have a long snout). As larvae, they generally feed on winter cereal crops and can sometimes hollow out cereal seeds. Adults generally feed on decaying vegetable matter, however in some situations they will attack emerging winter or spring-sown canola crops or lupins. They are capable of chewing plants above ground, ring barking or completely cutting stems.

Recently, damage from very high densities of vegetable beetles has been identified in a paddock of 2-5 leaf canola near Rupanyup in the Victorian Wimmera.

For more information refer to our Southern false wireworm Pest Note.

 

Eastern false wireworm (Pterohelaeus spp.)

While similar in appearance, both the larvae and adult stages of the Eastern false wireworm are often larger than the vegetable beetle and the bronzed field beetle. Adult beetles and larvae may damage plants by chewing stems at or below ground level, causing them to fall over or wither while standing. Larvae attack plant roots and germinating seeds, causing patchy germination of the crop. Generally larvae will only attack germinating crops if the soil is dry and if there is insufficient soil moisture and organic matter from which to feed.

Eastern false wireworm larvae have been identified as the likely culpit of large scale damage in an estasblishing cereal crop in the NSW South West Slopes in late June.

 

Eastern false wireworm is suspected to have caused the damage seen in the establishing paddock (Source: Tim Condon).

 

For more information refer to our Eastern false wireworm Pest Note.

 

Control of false wireworms

Foliar chemical applications can be used for partial control of some species of false wireworm that feed above ground, such bronzed field beetle adults. However, be aware that other species, such as vegetable beetle adults, are notoriously difficult to control at this time of year as they can tolerate high rates of many insecticides.

Chlorpyrifos is registered as a foliar spray against false wireworms in certain broadacre crops in some states. Poncho® Plus and fipronil-based seed dressings are also registered against wireworms in canola and other crops (e.g. sunflowers, sorghum). Although effective, seed dressings on their own may not provide adequate protection when pest numbers are high.

Understanding the lifecycles of false wireworms can help with planning of cultural management practices. Eastern false wireworm adults will lay eggs in close proximity to organic residue (such as stubble) from summer-autumn. Bronze field beetle adults also oviposit near organic residue, but the timing of egg laying is slightly different to its Eastern false wireworm counterpart – occuring after autumn rain from March-May. Cultural methods such as reducing stubble load, suitable crop rotations and cultivation over summer may be the best means of preventing the build-up of both adults and larvae in problem areas. 

It is important to be aware that once crop plants are advanced they will be able to out-grow most populations of false wireworms (adult and larvae).

 

Field observations

Tim Condon – Delta Agribusiness (South West Slopes, NSW)

Rob Fox – AGRIvision (Wimmera, VIC)

Karla Hosie – AGnVET (Riverina, NSW)