African black beetles

Agronomist, Sandy Middleton (AGnVET Services), has reported African black beetles causing damage to a wheat crop near Holbrook, in the South West Slopes district of New South Wales. Adult beetles have been observed just below the soil surface, mostly at the base of wheat tillers. Sandy reports typical feeding damage, which is characterised by beetles chewing plants at or just beneath ground level. A number of wheat plants are dead or dying as a result of feeding damage, and chemical control is being considered. The affected paddock was sown to canola last year, and before that, was long-term pasture.

African black beetles (Heteronychus aratoris) are soil dwelling, and favour pastures, particularly newly sown ryegrass. They also attack cereal crops, including barley, triticale and wheat. Populations can often build up in pastures and go unnoticed. In some seasons, African black beetles can take up to 2 years to complete a generation.

Adults are 12-14 mm long, cylindrical and glossy black in colour. Larvae are ‘C’ shaped with a brown head, 3 pairs of legs and can grow up to 25 mm long. Most damage is caused by adults, which emerge in autumn to early winter. Larvae are generally present from late spring to mid-summer and may feed underground on the roots of perennial grasses. As with most other soil-dwelling pests, the African black beetle is difficult to control with insecticides.

Increasing seeding rates is a useful management option in paddocks where African black beetles are anticipated to cause damage. If chemical control is required, spraying just prior to rain or late in the day is recommended as beetles often come to the surface at night. Insecticide seed dressings offer some protection to emerging seedlings. Sandy reported the affected wheat crop did not have an insecticidal seed treatment this year.