Exotic leaf miners
Exotic leaf miners – the pests that leave tracks
This is the fourth article in a series on emerging biosecurity risks that growers should have on their radar – these are pests or diseases that are not currently present in New Zealand, but are proving highly invasive around the world.
What are leaf miners?
Leaf miners are very small flies (only 1-2.5 mm in length) that are black and often have yellow spots on the head and body. The colour pattern on the adults differs depending on the species. Eggs are tiny, translucent and often whitish. The larval stages burrow into leaf tissue and are not usually seen, but larvae leave distinctive tracks or ‘mines’ as they feed on the upper leaf cells. The leaf mines are typically white wiggly lines on the leaf that get larger as the larva grows.
Why are they a problem?
There are over 300 species of leaf miner worldwide, a number of which are already present in New Zealand. However, some of the exotic species of leaf miner have the potential to become serious horticultural pests if they were to establish in New Zealand. Five species of Liriomyza are of particular concern. These are american serpentine leaf miner (Liriomyza trifolii), vegetable leaf miner (L. sativae), tomato leaf miner (L. bryoniae), pea leaf miner (L. huidobrensis) and striped leaf miner (L. strigata).
Plant damage can occur in a number of ways but it is generally the larval stage of the insect that is most destructive. Larval feeding significantly damages the interior of the leaf which reduces the photosynthetic capability of plants and impacts on yield. Adult feeding and egg laying can cause leaf punctures, stippling and mechanical transmission of plant viruses. Leaf mines and punctures provide an entry point for pathogens, increasing the chance of secondary fungal infections.
What crops do they attack?
The host range varies for each species, but exotic leaf miners affect many important vegetable crops, including tomatoes, potatoes, celery, brassicas, cucurbits such as melons and pumpkins, and legumes including peas and beans. A range of feed crops (for example maize and clover) and many ornamental species are also hosts.
Distribution and spread
The leaf miners of concern to New Zealand have different distributions, but are generally widespread through Africa, America, Europe, Asia and parts of Oceania.
Risk to New Zealand
The highest risk for long distance spread to new areas is via transport of plant material or associated goods containing larvae such as infested plants, leaf material, soil or packaging. Adult flies are highly mobile and spread rapidly throughout a crop once established. Leaf miners are particularly problematic in protected cropping systems. What to do if you see it
If you think you’ve seen an exotic leaf miner call the Ministry for Primary Industries (MPI) pest and disease hotline on 0800 80 99 66.