Lowering the risk of Vegetable leafminer

The Vegetable leafminer (Liriomyza sativae; VLM) is an exotic fly species which poses a significant threat to Australia’s nursery and vegetable production industries.

VLM established itself in the Torres Strait in 2008 and was found on the mainland of Australia on the Cape York Peninsula in 2015. VLM populations have not reached problematic levels in Australia as researchers believe that tiny biological control agents called parasitoid wasps are helping parasitise leafminer flies.

Levy funded ‘Research, Development and Extension program for control, eradication and preparedness of vegetable leafminer’ (MT16004) project launched in 2017 to better identify and recognise the impact VLM could have on Australia’s nursery and vegetable production industries and where parasitoid wasps could contribute to controlling the pest.

What are parasitoid wasps?

Parasitoid wasps attack leafminer flies. Female wasps lay their eggs on or inside fly larvae or pupae, and when the eggs hatch, the wasp larva eats the fly larva/pupa before completing its development and emerging as a new adult wasp.

Australia has at least 50 species of parasitoid wasps that are known to infest native leafminer flies, presenting an opportunity for the biological control of VLM using species already established.

An ally in the fight against VLM

As part of the project, research has been conducted surrounding the impact of parasitoid wasps’ on preventing the establishment of VLM in Australia and how incursions can be effectively controlled.

Project lead and Cesar Research Scientist, Dr Elia Pirtle, has undertaken extensive field research in the Torres Strait and Cape York Peninsula studying parasitoid wasps and their relationship with VLM.

Findings have revealed several Australian species of the wasp has shown to be effective at controlling VLM on the incursion front in far-North Queensland. At least six species of parasitoid wasps have proven to attack VLM with some cases revealing unassisted field rates of parasitism to reach as high as 80 per cent.

The project team acknowledge that there may be multiple factors contributing to the limited spread of VLM, however it is predicted that the high population of parasitoid wasps are what is lowering the risk of the pest spreading.

Chemical concerns

Whilst parasitoid wasps are controlling far-north Queensland’s VLM population, the wasps are highly sensitive to chemicals and are at risk of being wiped out when a crop is sprayed. This is referred to as a secondary pest outbreak, meaning that it is not until its natural enemies are destroyed that the surviving leafminers become a problem for growers. This demonstrates the importance of conserving parasitoids in Australia, as the foundation of a successful integrated pest management system.

Whilst Australian agricultural regions remain free of VLM, it is essential for growers to conserve parasitoid wasp populations and factor their contribution into on-farm pest management practices.

Future research looks to define how parasitoids might affect VLM populations in Australian nursery and vegetable production regions but can so far assert that this approach will assist growers in successfully managing potential incursions.

Find out more

For more information, contact GIA National Biosecurity Manager John McDonald at john.mcdonald@greenlifeindustry.com.au or on 07 3277 7900. Alternatively, you can visit the project page on the AUSVEG website.

Any unusual plant pest should be reported immediately to the relevant state or territory agriculture agency through the Exotic Plant Pest Hotline (1800 084 881).

The ‘Research, Development and Extension program for control, eradication and preparedness of vegetable leafminer’ (MT16004) project has been funded by Hort Innovation using the vegetable, nursery, melon, and potato research and development levies and contributions from the Australian Government.

This article is reproduced with the permission of AUSVEG.