Natural enemies building-up

There have been several reports indicating many natural enemies, such as ladybird beetles, lacewings, hoverflies and parasitic wasps, building-up in numbers in various locations. Agronomist, John Stuchbery (John Stuchbery and Associates), has reported a high level of beneficial insects in parts of the Wimmera and Mallee, in Victoria. John also reports that aphid numbers in cereal crops have stabilised and begun to decline in many areas. Paul Horne (IPM technologies) says many natural enemies have significantly increased in numbers across the Western district of Victoria. In particular, a high number of parasitic wasps and brown lacewings have been observed and are providing good control of aphids in many cereal crops.  

Ladybird beetle:

Ladybird beetle (Family: Coccinellidae) adults and larvae are predatory and consume prey. Adults are round to oval in shape and typically bright orange in colour with black spots on each wing-cover. Occasionally, they can be completely black or orange. The larvae are more elongated than adults with the rear of the body tapering. They are grey or black in colour with orange/yellow markings across the body and may be covered in spines or white fluffy wax material. For images refer to: common spotted ladybird and white collared ladybird.

Lacewings:

Lacewings (Order: Neuroptera) are voracious predators, attacking a range of prey. The adults, which are between 6-15 mm long, have wings that are folded over the abdomen in an inverted ‘V’ shape and have numerous veins, giving a lacy appearance. Larvae are up to 8 mm long and have protruding sickle-shaped mouthparts and a tapering body. The adults and larvae of brown lacewings are both predatory, while only the larvae of green lacewings are predators.

Hoverflies:

Hoverfly (Family: Syrphidae) larvae are generally green in colour with a whitish stripe down the centre of their back. The larvae are grub or maggot-like (with no visible legs), and can be mistaken for pest grubs such as the diamond back moth. They grow up to 8-10 mm long, have a pointy-head region that moves rapidly from side-to-side and importantly, are predatory.

They attack aphids, spearing them with their pointed jaws. They generally hold the aphids upright and suck out the contents. Adults are 4-7 mm long and have a dark-coloured, flattened body with black and yellow markings. As their name implies, they can hover or fly swiftly. Like all flies, they only have one set of wings. Adults do not feed on insects. For images, click here.

Parasitic wasps:

A number of aphid ‘mummies’ have been reported in the field and observed in samples sent in for identification. This indicates the activity of parasitic wasps. Female wasps will often insert an egg into an aphid and the developing larvae feed inside the aphid, eventually killing it. The new adult wasp emerges from the mummy by cutting a hole in the skin. Adult wasps are small, usually dark in colour and difficult to detect. For images, click here.

It is important that natural enemies are correctly identified before deciding on control strategies. They are a useful form of control during spring and when low to moderate numbers of aphids are present. If chemical control is necessary, consider using ‘softer’ chemicals (such as pirimicarb) which are aphid-specific and less harmful to natural enemies. Peter Mangano (Department of Agriculture, WA) recommends that if a systemic insecticide such as dimethoate is chosen, there will be no added benefit in mixing an ‘anti-feed’ synthetic pyrethroid this late in the season. Peter says that synthetic pyrethroids are much less effective at killing aphids than systemic insecticides and should only be used where registered, in the very early crop growth stage and where risk of plant diseases such as barley yellow dwarf virus is high.