Hoverflies & other natural enemies

There have been several reports from agronomists and farmers indicating a number of natural enemies, such as ladybird beetles and lacewings, are building up in various locations of Victoria. In particular, a number of insects sent in for identification have been identified as hoverfly larvae. Hoverfly larvae (Family: Syrphidae) 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. Research Officer, Judy Bellati (SARDI), has also identified a number of hoverfly larvae in samples from South Australia in the last few weeks.

Hoverfly larvae are blind, with a pointy-head region that moves rapidly from side-to-side. They grow up to 8-10 mm long 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.

A number of aphid ‘mummies’ have also been reported in the field and observed in samples sent in for identification. This indicates the activity of parasitic wasps. Small 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.

It is important that hoverflies (and all natural enemies) are correctly identified before deciding on control strategies. They are a very reliable form of control during the warmer days of spring and when low to moderate numbers of aphids are present. Agronomist, Kate McCormick (John Stuchbery and Associates), says aphid numbers in the Mallee region of Victoria have declined over the last few weeks, at least partially due to the presence of natural enemies.

A workable management threshold guide for aphids is between 10-20% of plants heavily infested. If more than 20% of plants are infested, chemical control to suppress aphid numbers and avoid yield loss should be considered. If chemical control is necessary, use ‘softer’ chemicals (such as pirimicarb) which are aphid-specific and less harmful to natural enemies.

Click here for images and further information on hoverflies.