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Wireworms and bronzed field beetles

Agronomist, Adrian King (SMS Rural Services), has reported finding patches of damage to a canola crop west of Warracknabeal, in the Wimmera district of Victoria. Upon closer inspection, several true wireworm larvae were found along with distinctive ‘ringbarking’ damage to affected plants. Adrian says most damage was found in low-lying areas of the paddock that were quite wet earlier in the year.

True wireworms and bronzed field beetle larvae have been identified for research agronomist, Diana Dunstan (AgriTech Crop Research), from two trial sites in South Australia. True wireworms were found in a wheat trial west of Naracoorte, in the Lower South East district and bronzed field beetle larvae were found in oats undersown with clover north of Naracoorte, in the Upper South East district. Diana says no damage was evident in either instance despite easily finding several larvae per square metre at both sites.

True wireworm (Family: Elateridae) larvae grow between 15-40 mm long and feed on underground roots, seeds and stems. They attack pre- and post-emerging seedlings of all oilseeds, grain legumes and cereals. Adults are native beetles that are commonly called ‘click’ beetles due to their habit of springing into the air with a loud click when placed on their back. For further information about true wireworms, refer to PestFacts Issue No. 4.

Bronzed field beetle (Adelium brevicorne) larvae are dark brown, up to 12 mm in length and about 3 mm wide. They have twelve body segments, and the last segment has two distinct upturned spines. Bronzed field beetles are a type of false wireworm (Family: Tenebrionidae), and are often confused with true wireworms and other false wireworms, particularly grey false wireworm larvae. Adult beetles are up to 11 mm long and shiny black in colour with a slight bronze appearance.

Bronzed field beetles damage plants by chewing on seedlings at or above ground level. They are important pests of establishing canola and typically do not affect cereal and pulse crops. Larvae are typically found within the top 1 cm of the soil and can be found under plant material, clods of soil, rocks or wood. Although they may also feed on roots and underground stems of plants, they can be present in the soil with little or no damage to plant seedlings. This is because they primarily feed on dead organic matter and high numbers are required to cause significant crop damage.

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