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Flies

Flies – an overview:

This page provides an overview of pest flies in vegetable crops. The related tools listed at the end of the page provide detailed information about their identification, damage and management. It is important to be able to identify insect pests such as flies, and to have unknown species expertly identified so that they can be appropriately managed. Several fly species are beneficials and help to control other pests of vegetable crops.
Flies can cause extensive damage to agricultural crops by laying eggs in plant material, particularly maturing and ripe fruit. Subsequently fly larvae feed on stems, roots and the fruit. Some flies spread soft rot organisms. Flies have a major economic impact on vegetable production, as they make the crops unfit for market. Integrated pest management of flies requires extensive and focused crop monitoring and scouting.
There are a exotic flies such as Vegetable leafminer (Liriomyza sativae) and Carrot rust fly (Psila rosae) which would pose a serious threat to Australia's plant industries should they enter Australia and become established.

Types, hosts, and damage:

Types of flies

Description

Host vegetable crops

Primary damage
Two-spotted (spider) mite (Tetranychus urticae) The adult fly is grey and 3 mm long. Lettuce. Severely mined leaves can wither and die and make lettuce unmarketable.
Tomato russet mite (Aculops lycopersici) Medfly adults are 3-5 mm long, light brown, with distinct brown bands extending to the wing tips. QFF are red-brown with yellow marks, and are about 8 mm long. A wide range of fruits and vegetables. After laying eggs in the fruit, some necrosis may be visible around the puncture mark. These sting marks can cause fruit to be rejected at market. This is usually followed by decomposition of the fruit. Makes fruit inedible, with severe consequences for local and international trade.
Broad mite (Polyphagotarsonemus latus) Similar to QFF, adults are reddish-brown with yellow stripes and are about 8 mm long. Cucurbits. Causes puncture marks and deformities on immature fruit. Egg-laying sites and larval feeding in maturing and ripe fruit encourages fruit rotting organisms.
Red-legged earth mite (Halotydeus destructor) Important in hydroponic/greenhouse production. Adults are small, slender, black or dark brown, with long dangling legs and antennae. Greenhouse vegetables; Leafy vegetables. Larvae feed on organic matter and roots and tunnel into stems at and below the soil line. Larvae and adults can spread Black root rot, Pythium and Fusarium root diseases. Adults can spread the foliar disease, Botyritis.
Bean spider mite (Tetranychus ludeni) Important in hydroponic/greenhouse production. Adults are small, black, with reddish eyes and 5 pales spots on each wing. Greenhouse vegetables; Leafy vegetables. Indirectly damages plants by spreading Black root rot, Pythium and other soft rot organisms. Adults leave faecal material on leaves.
Bean fly (Ophiomyia phaseoli) Adult flies are about 3 mm long with a shiny black body and clear wings.  Beans.  Larvae cause damage by tunnelling into plant tissue. Severe infestations can cause seedling death.

Management:

Control methods for flies include cover sprays, bait sprays, and traps. Usually intensive eradication programs include surveillance, trapping, and spraying host materials such as fruit and trees with organic bait. Cultural control is important for fruit flies and fallen fruit should not be allowed to accumulate. There are a number of parasitoids that kill flies in the pupal stage, which helps to reduce the next generation of flies. The release of sterile fruit flies in outbreak areas reduces the wild fruit fly population by limiting opportunities for the pest to successfully reproduce. Queensland fruit fly (QFF) is one of the world’s worst horticultural pests. The threat of QFF is so serious that a number of quarantine (exclusion) zones have been established nationally, and the movement of fruit and vegetables is restricted so as to prevent its spread. Quarantine measures are also in place for Mediterranean fruit fly. Shore flies and fungus gnats are controlled by eliminating rotting vegetation, weeds and algae around the growing structure. Chemical controls are available. The beneficial, Hypoaspis, is a fungus gnat predator.

Beneficial flies:

There are a number of beneficial flies which help in the control of pests. These include:
  • Hover flies – Larvae attacks aphids by holding them with their pointed jaws and sucking out the insect juices.
  • Tachinid flies – Larvae attack a wide range of insect pest species including Helicoverpa, loopers, armyworms, locusts and grasshoppers.
  • Green vegetable bug parasitic fly – Fly larvae hatch and bore into the host green vegetable bug resulting in the bug to stop feeding.

Source of information and related tools: