Ex­otic leaf min­ers

NZ Grower - - News - By Leanne Stewart Leanne Stewart is biose­cu­rity man­ager for Hort NZ. Source:https://www.flickr.com/photos/gbohne/

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.

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