POMEWEST Medfly

In Western Australia, the apple and pear industry’s national R&D program, PIPS 4 Profit is investigating the feasibility of classical biocontrol for Ceratitis capitata, Mediterranean fruit fly (Medfly) and augmentative biocontrol for Epiphyas postvittana, light brown apple moth (LBAM). This year is focused on Medfly, after our baseline monitoring indicated good conditions for the native parasitoid Diachasmimorpha kraussii.

Words Jen Riseley, Project Officer, Pomewest

INITIAL monitoring of both pest species for 2024–25 is now complete, and a location in the Donnybrook townsite was selected for the release of the biocontrol agent against Medfly. The site sits close to many household orchards and includes unmanaged habitat along the Preston River, offering good shelter and nectar sources for parasitoids. Interestingly, the features that make this a challenging area for managing Medfly are the same factors that make it a promising site for a parasitoid release.

Mid January was identified as the best release period, matching pest activity from the project’s first year. Although fruit flies appeared in early December, there were likely too few larvae for parasitoids to target. A spike in adult Medfly numbers in mid to late January 2025 suggested larvae had developed about a week earlier.

Because D. kraussii targets 2nd and 3rd instar larvae, releases are most effective during these spikes when egg laying opportunities peak. In January 2026, a similar rise in trapped Medfly occurred a week before the scheduled release. In summer temperatures of 25–30 °C, the life cycle of both Medfly and D. kraussii is 27–30 days (see Figure 1).

Live adult D. kraussii parasitoids were sourced from Agriculture Victoria’s Tatura laboratory colony. As the biocontrol agent is a larval parasitoid, it requires a fruit fly larva to complete a full life cycle. In Victoria, Qfly larvae are used to feed immature parasitoids in the laboratory colony. Once the adult parasitoids emerge, they move about freely and can be separated from their fruit fly hosts. These isolated adults are then fed a honey and water mix.

FIGURE 1. Life cycle of Medfly and parasitoid D.kraussii.

To eliminate any possible risk of contamination, D. kraussii could only be transported into WA as fully emerged, isolated adult individuals, accompanied by a quarantine clearance from WA DPIRD. The adult parasitoids were packaged with a wet sponge as a water source to board the four hour flight, but no honey from Victoria was allowed to be added. Upon landing in WA, the wasps were transferred to an insect cage and quickly fed WA honey mixed with water.

Greg Lefoe of Agriculture Victoria, Jennifer Riseley and Susie Murphy White of Pomewest at Busselton Airport.

D. kraussii on a pear, hunting for larvae.

Three days after hatching, female parasitoids are most active in seeking males. Both males and females were reared in the laboratory under good conditions, with more females than males available for the release.

No fatalities were seen during the transport and release process, resulting in 250 live specimens being released in Donnybrook on 14 January 2026 at a temperature of 28 °C.

Average temperatures over the following week remained in the mid 20s, with highs of 30–35 °C.

Parasitoid vs predator

Insect terminology can be confusing, and while it’s easy to think of D. kraussii as a predator, it is more accurately described as a parasitoid. Insect predators are mostly generalists, meaning they hunt different kinds of prey and rapidly consume many organisms throughout their lifetime — common examples include ladybirds or praying mantids. Parasitoids are specialists that lay their eggs within a single host, causing the death of that individual organism. They are also often smaller than the host species. This highly specialised nature of parasitoids makes them a lower risk for biocontrol releases as they are less likely to harm non-target species, and are more effective at targeting a specific pest of concern.

After the initial Donnybrook release, persistence is being measured fortnightly using Medfly infested fruit as bait, with laboratory rearing used to check for emerged adult parasitoids.

Producer interest in parasitoids for biocontrol varies depending on the situation, with growers near townsites, abandoned orchards, or rivers with escaped fruit trees finding the most value in a biocontrol option.

PIPS 4 Profit website: www.apal.org.au/pips-4-profit-program

The IPDM Manual for Australian Apple and Pears is your primary industry resource for the identification and management of pest and disease.

Jen Riseley, jen.riseley@dpird.wa.gov.au