Enhancing future preparedness for vegetable leafminer

This article is reproduced with the kind permission of AUSVEG and provides an update on the ongoing strategic levy investment project for the vegetable leafminer. The project involves many research, development and extension activities that will help the Australian vegetable and nursery industries prepare for the pest. AUSVEG Biosecurity Officer Madeleine Quirk speaks to Dr Peter Ridland, an entomologist at the University of Melbourne, to find out more.

Project MT16004 – RD&E Program for control, eradication and preparedness for Vegetable Leafminer (2017-2020), a strategic levy investment under the Hort Innovation Vegetable and Nursery Funds, brings together cesar, the University of Melbourne, Plant Health Australia, the Northern Australia Quarantine Strategy and AUSVEG to undertake a number of activities to prepare for the vegetable leafminer (VLM).

Since 2008, the VLM has been moving down the Torres Strait Islands and in 2015, the pest was detected on the Cape York Peninsula in northern Queensland. MT16004 was developed in recognition of the impact that the VLM could have on Australian vegetable and nursery production industries if it were to move into vegetable and nursery production areas.

The project has many facets, including: identifying spread pathways of the VLM to Australia; modelling the spread from Cape York Peninsula; investigating biological and chemical control; developing management guidelines and trapping methods; developing a VLM contingency plan; and communicating updates as they arise throughout the lifetime of the project.

What is the vegetable leafminer?

The VLM is one of a small group of agromyzid leafminers that attack a very wide range of host crops, primarily in the Cucurbitaceae, Fabaceae and Solanaceae families. They can also move readily between non-crop and crop plants.

The feeding habits of these pests can be devastating to crops. High levels of mining reduce yield and can also lead to premature defoliation in some crops.

“The adult female fly scrapes circular feeding holes in the plant surface with her ovipositor,” University of Melbourne entomologist, and consulting entomologist on the project, Dr Peter Ridland said.

“This damage can facilitate infection by some plant pathogens including bacteria, fungi and viruses,” he continued.

Eggs are also laid in some of these feeding holes. Legless larvae hatch and feed internally, forming the characteristic mines in the leaf. However, larvae are generally held in check by generalist parasitoid wasps, which lay their eggs inside other insects or beside other insect larvae, including agromyzid flies.

Current project findings and future activities

Dr Ridland is reviewing global scientific literature on biological control options for VLM and is compiling a comprehensive overview of research previously conducted in Australia on agromyzids and their parasitoids. In his experience, the review has been important in setting the direction for research in biological control strategies for VLM.

A key finding of the research team has been the recognition that Australia already has a large number of generalist parasitoid species attacking endemic agromyzids and that it will not be necessary to import foreign species as biological control agents for VLM.

“Our challenge will be to utilise existing parasitoid wasps effectively in VLM management while recognising the constraints placed by pest management requirements for other key pests in the crops,” Dr Ridland said.

“The second year of the project will see a major emphasis on collecting and rearing parasitoid wasps from a range of agromyzid hosts in the major horticultural areas in eastern Australia.

“We intend to define the distribution of the parasitoid, Diglyphus isaea, which to date has only been found in south-eastern Australia.”

Dr Ridland and the project team are also very interested in receiving reports of leafmining activity on crop and non-crop plants from growers and consultants.

Could research efforts be applied to other leafminer species?

Dr Ridland added that the information gained from MT16004 on the Australian fauna of generalist leafminer parasitoids will also be directly applicable to two other closely related leafminer species, L. huidobrensis and L. trifolii. These species are currently found in south-eastern Asia and some nearby Pacific Islands, and both pest species are considered to be more damaging pests than VLM, largely due to the high level of insecticide resistance in the invading populations found in Asia.

Key project personnel

University of Melbourne entomologist Dr Peter Ridland’s extensive experience is of great value to the vegetable leafminer project.

Dr Ridland has worked on many different pests of field crops, pastures and vegetables at the Victorian Department of Agriculture (1974-2005) as well as completing his PhD on the biology and ecology of cereal root aphids at La Trobe University in 1988. He also worked on a series of entomological projects in Indonesia looking at pests of vegetables and potatoes in the 2000s.

“I was fortunate to lead an ACIAR project looking at two invasive pests which were considered to be potentially very important pests in Australia: vegetable leafminer ( Liriomyza sativae) and potato leafminer ( L. huidobrensis),” he said.

Dr Ridland has an abiding interest in helping farmers manage pests by promoting natural enemies (including parasitoids and predators) in crops by avoiding indiscriminate use of broad-spectrum insecticides and using more specific chemicals in a targeted fashion.

“Our knowledge and experience from the ACIAR project has provided a solid foundation to the Hort Innovation project,” he stated.

Dr Ridland also plays a role in developing a contingency plan for VLM, which is being led by Plant Health Australia. He is also assisting other project members with their sub-projects where required and he sits on the Project Steering Committee.

In addition, Ary Hoffman (University of Melbourne) and Paul Umina ( cesar and University of Melbourne) are working alongside Dr Ridland to co-supervise a Masters student, Marianne Coquilleau, whose focus is to determine the distribution and diversity of leafminer parasitoids in key vegetable and nursery production areas in Australia. Her work will involve sampling main agromyzid leafminer species and parasitoids and use molecular tests to identify them.

Xuefen-Xu from Sun Yat-Sen University in China has just enrolled as a PhD student and she is likely to be looking in detail at the genetic structure of VLM populations around the world to assist in the pathway analysis of VLM being undertaken in the project.

For more information, contact NGIA National Biosecurity Manager on 07 3277 7900 or john.mcdonald@ngia.com.au. Alternatively you can visit the project page on the AUSVEG website at ausveg.com.au/biosecurity-agrichemical/biosecurity/mt16004/.

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).

This project has been funded by Hort Innovation using the nursery and vegetable research and development levies and contributions from the Australian Government. The Vegetable and Potato Biosecurity Program is funded by the Plant Health Levy.

Project Number: MT16004

First published in Vegetables Australia July/Aug 2018

More images can be accessed here, courtesy of Elia Pirtle, cesar