What was it all about?

Since the 1960s, dimethoate and fenthion have been used by apple and pear, stone fruit and mango growers for pre-harvest and post-harvest control of Mediterranean fruit fly (Medfly). The loss of these insecticides in 2011 and 2015, respectively, makes Medfly more difficult to control in highly susceptible crops.

This project developed and tested several pre-harvest control tactics that could assist growers of Medfly host crops in Western Australia. Parts of an area wide management program were tested in pome and stone fruit orchards in Jarrahdale in the Perth Hills, and mass trapping was trialled in an area within the Jarrahdale town-site.

Traps showed when and where Medfly was abundant, and provided feedback on how effective the control measures were.

The main findings of the program were:

• Medfly was found to survive winter in the adult and immature stages in all Perth Hills areas
• There are two main periods of Medfly abundance: summer and autumn
• Spring infestation of commercial orchards was attributed to overwintered flies, rather than an influx of adults from nearby areas such as towns
• In autumn, Medfly adults disperse into surrounding areas to search for suitable over-wintering sites. Late autumn baiting is recommended to curb these dispersing adults, coupled with strict orchard hygiene to eliminate overwintering eggs and larvae.
• Area wide management with bait sprays was highly effective at suppressing Medfly, even with as few as three growers
• The sterile insect technique did not reduce the Medfly population below the economic threshold when used alone
• Trap and lure components that growers could use to develop their own mass trapping system were identified, as well as lures to improve monitoring of male Medfly
• Neonicotinoids currently available for use under an APVMA permit, Samurai Systemic Insecticide (clothianidin) and Calypso (thiacloprid), killed Medfly eggs and larvae when fruit was treated seven days after Medfly had been allowed to lay eggs. They are both possible replacements for fenthion.

The researchers concluded that growers should adopt area wide management of Medfly even if the whole area is not involved, since trials showed that even small groups of growers achieved suppression with weekly to twice weekly applications of bait sprays.