Fruit fly monitoring in commercial orchards

Page last updated: Thursday, 30 August 2018 - 11:11am

Please note: This content may be out of date and is currently under review.

Monitoring is an essential part of a commercial fruit fly management program, involving trapping and regular fruit inspection for ‘stings’ and larvae.

Monitoring forewarns growers of changes in the fruit fly population, and if comprehensive records are kept, they can be used to understand seasonal abundance patterns and to identify recurring 'hot spots'.


Male lure

  • Male medflies are attracted to trimedlure, which is available commercially as plugs or wafers.

Female lure

  • Female lures are based on food attractants. They can also attract some males when medfly populations are high.
  • Biolure and Unipak are mixes of three attractant chemicals available commercially: trials indicate that there is little difference in attractancy between them.

Trap types

  • A wide range of traps are commercially available, and new fly traps come out all the time. Most of these have a yellow base and a clear plastic lid.

Killing flies in traps

A range of killing methods can be used:

  • DDVP (diclorvos) is commercially available. It knocks down and kills insects entering the trap.
  • Sticky trap inserts.
  • Water.
  • Propylene glycol is better than water as it does not evaporate as quickly.
  • Some newer traps already have the killing agent incorporated into the lid.

How often are lures replaced?

Female lures and DDVP should last for at least three months. Male lures may need to be changed after eight weeks.
When changing lures, make sure that you use gloves, and dispose of the lures away from the traps.

Trap placement

  • Research suggests that at certain times of the year, for example, early in the season, more males are trapped than females. By using both types of traps, you increase the sensitivity of your monitoring program.
  • Hang traps in pairs (one male, one female) in fruit trees about 1.8m from the ground. Each trap in the pair should be at least 25m apart.
  • Place at least one trap per hectare, or one trap per block.
  • You can move traps from blocks a few weeks after picking, to the next block where fruit is ripening.

When do I start monitoring?

  • Start monitoring from fruit set and check traps weekly. Keep records of how many flies are caught in which traps. This information is usual for identifying 'hot spots' within the orchard, and for reviewing your fruif fly management program.

Male or female?

male and female medfly
Female and male Medfly
  • Almost all flies caught in male traps will be male. However, male and female medfly can be trapped in female traps.
  • Males have ‘clubs’ on their head, females do not. Females also have ovipositors (used to insert eggs into fruit) and males do not.

What do the trap catches mean?

  • If no flies are being caught, this means that there are none to few Medfly present on the orchards. However, stone fruit may still be affected by the few flies that do not move to traps. For this reason, you should also check fruit for stings.
  • More than one fly - start baiting.
  • Sustained high fly numbers indicate that there is a major problem. Review your medfly management, for example bait application, orchard hygiene and consider using a cover spray.

How many traps do I need?

  • At least two traps per hectare (one male, one female), with a minimum of four traps per orchard (two male, two female) are recommended.