POMEWEST biological control

Integrated pest and disease management (IPDM) focuses on biological, cultural and chemical control options to produce high quality fresh produce while minimising harmful effects on the environment.

Words Jen Riseley, Project Officer, Pomewest

IPDM involves regularly checking for pests and beneficial insects, then using biological and cultural methods to control pests, with selective chemicals only used when necessary and in a way that does not harm beneficial insects. Preference is for using the least disruptive pesticides to natural enemies in the orchard. Bait spraying, mass trapping and sterile insect release often does not target the larval or egg stage, which leaves an opening for parasitoids as a management option.

Different types of biological control

Classical biocontrol is usually defined as the introduction of a non-native organism to target a non-native pest and bring down pest density levels. As a component of the apple and pear industry’s research and development program, PIPS 4 Profit — Pest and Disease Management project (AP22001), a form of classical biocontrol is being studied to control the exotic Mediterranean fruit fly. This research is investigating the native wasp Diachasmimorpha kraussii, as a ‘classical biocontrol’ of Mediterranean fruit fly (Medfly) in areas where the biocontrol agent does not normally occur.

Conservation biocontrol preserves a population of natural enemies already in the affected environment. These methods include providing habitat such as flowering plants near an orchard or headland as a habitat and food source for lacewings or ladybirds as is being investigated in the PIPS 4 Profit — Building Sustainable Soils project (AP22003) trial site, located in Manjimup.

PHOTO: https://agriculture.vic.gov.au

Augmentative biocontrol involves increasing the population of natural enemies by periodically releasing more into the environment. Trichogramma is an example of augmentative biocontrol as Trichogramma spp are native across Australia, including WA.

Beneficial insect species can keep pest populations below thresholds for broad-spectrum pesticide use.

What is a parasitoid?

Unlike a predator or a parasite, a parasitoid uses a host insect (a pest in this case) to reproduce. For instance, some parasitoid wasps will lay eggs into live aphids, eventually killing the host as the larva matures. Parasitoids are usually very specialised, often targeting only one species. The advantage is a successful parasitoid will kill the host, while a successful parasite requires a host to survive to keep feeding on it and is not often successful for long term management. The parasitoids being investigated in the PIPS 4 Profit program include Trichogramma carverae which lays its eggs in the egg of both light brown apple moth and codling moth, and Diachasmimorpha kraussii which lays eggs in the larvae of Medfly and other fruit fly species.

More general predators like lacewings and ladybirds are familiar to producers and attack various egg-laying pests. Predators generally feed on a large number of pests or prey in their lifetime, rather than just one at the beginning of the life cycle.

Examples of parasitoids currently in use in WA

• Trichogramma spp are used worldwide for control of codling moth and light brown apple moth. The PIPS3 Program (2020–23) demonstrated suitability in eastern Australian orchards.

• DPIRD have recently started a flesh fly biorelease for conical snails in wheat crops near Esperance, after the flies were sourced from Montpellier, France, and bred at Yorke Peninsula in SA.

• Diadegma parasitic wasps are used on the Spinosad-resistant diamondback moth in brassica crops, though are highly sensitive to sprays.

Examples of other biocontrols in Australia

• Skeleton weed gall midge and the associated rust fungus was successfully used to target the invasive skeleton weed in the eastern states. It is estimated to have saved $1.4 billion to the Australian economy and is now being released in WA.

• Australia exported the vedalia beetle to California to successfully protect citrus against cushiony scale.

• Twelve species of dung beetle have been introduced and established in Western Australia to control bush flies.

• Rabbit biocontrols will be familiar to most, released viruses include calicivirus, myxomatosis and RHDV1 K5. Eventually resistance will form as a successful virus does not kill the host.

• Dock moth was introduced from Morocco to target the invasive dock weed, research in the 1980s showed it was harmless to all other crops and a joint project between DPIRD and Meat Livestock Australia saw numerous releases in high rainfall pasture areas of the south west.

Ideally biocontrols are self-sustaining once released and established, not requiring annual or more frequent releases.

Spotlight on the tiny wasp Diachasmimorpha kraussii

Diachasmimorpha kraussii is native to northern and eastern Australia and has successfully been introduced to Hawaii and Israel for fruit fly control, with the wasps still detected 3 years after release. A previous Hort Innovation supported project, Parasitoids for the management of fruit flies in Australia (MT19003) was able to successfully mass rear and establish populations in a peri-urban environment in Northeast Victoria. Diachasmimorpha krausii has also been detected in the Perth metro area from 2021, within its natural distribution of southwestern and northern Western Australia (Figure 1).

FIGURE 1: Distribution of D. kraussii in Australia as of 2021.

Source: Clarke et al. 2021.

FIGURE 2: Parasitoid wasp process.

Source: Supplied by Agriculture Victoria, redrawn from Jenkins et al. (2012) Insects 3 763–788.

Diachasmimorpha kraussii is a polyphagous species 3–5mm long, associated with parasitising 13 species of Bactrocera fruit flies as well as Medfly and has success targeting non-tropical fruit types, a favourable trait in a commercial biocontrol. The wasp first identifies ripening fruit before looking for target larvae, so the ability to locate and target temperate fruit like pome and stone fruits is crucial to biocontrol success. Many other parasitoids have failed to target non-tropical fruit in previous attempts to establish a biocontrol agent population in WA. The process of parasitising fruit fly can be seen in Figure 2.

As the species are not commercially available, the PIPS 4 Profit program aims to release D. kraussii, raised in laboratory conditions at Agriculture Victoria, into peri-urban townsites facing Medfly pressure.

Town-sites with relatively high pest numbers are preferred for initial biocontrol agent releases because they increase the likelihood of biocontrol agents establishing long-term populations in the area. Most commercial orchards use preventative options for various pests, and low pest numbers in these orchards could impede initial biocontrol agent establishment. The peri-urban sites will be monitored for establishment of D. kraussii over several seasons. The desired benefit to the industry from a biocontrol agent becoming established in townsites is reducing pest pressure from residential or unmanaged fruit trees often seen in regional cities and towns.