Beneficial invertebrates

Many groups of beneficial invertebrates have been slow to build up in crops this season however there has been a significant increase in numbers in many areas over the last few weeks. This may be of little consequence in regions where crops are already close to harvest and/or pests have already built up to high numbers requiring chemical control. However, beneficial species will be important and provide some level of pest suppression in later growing and irrigated crops.

Research agronomist, Simon Craig (Birchip Cropping Group), reports high numbers of ladybird beetles (Family: Coccinellidae) in a vetch crop that is being attacked by aphids, near Birchip in the Mallee district of Victoria. Researcher, Stuart McColl (cesar), has also found a significant increase in ladybird numbers at a research trial site near Elmore in the Northern Country district of Victoria. Both adult and larvae ladybird beetles consume prey including aphids, leafhoppers, thrips, moth eggs and small larvae. Hoverflies (Family: Syrphidae) have been identified for several agronomists from samples collected in canola and forage brassica crops in western Victoria and the Central West Slopes and Plains district of New South Wales. Hoverfly larvae are grub or maggot-like (with no visible legs), and are often mistaken for pest caterpillars. They grow up to 10 mm in length and importantly, are efficient predators of aphids.

Other beneficial species likely to be encountered at this time of year include spiders (Order: Araneae), parasitic wasps (Aphidius spp.) and lacewings (Order: Neuroptera). A thorough inspection of the crop and identification of beneficial species present is recommended prior to making a control decision. If chemical control is warranted, insecticides that are less toxic to beneficial species should be considered.

For more information on beneficial invertebrates refer to PestFacts Issue No. 12.