Leaf Miner Identification

• Three species of leaf miner flies lay their eggs on tomato plants. All have black and yellow coloring. Liriomyza trifolii's head at the back of its eyes is almost entirely yellow, while its upper body is shiny black and its thorax, or area directly behind the head, has a covering of bristles. L. huidobrensis is a larger insect with markings similar to L. trifolii's. L. sativae also has a shiny, black upper body. Its lower face is yellow, and it has yellow triangles at the bases of its wings.
  
  

Life Cycle

• All three of these leaf miner flies attack a variety of crops, including tomatoes. They deposit their eggs inside leaves. Their newly hatched larvae feed on the inner leaf tissue, forming those white tunnels as they go. The older worms leave their tunnels and fall to the ground, where they spin cocoons and emerge as adult flies. The insects mature from hatchlings to adults in just two weeks. While the flies lay their eggs throughout the growing season, infestations are heaviest later in the summer.
  
  

Damage

• Heavy infestations of leaf miner larvae can produce tunnels that develop into white blotches. They cause early leaf drop on tomatoes. In the worst scenario, they can leave a plant nearly defoliated and stunt its growth. Leaf loss that occurs as the tomatoes start to fruit results in smaller fruit and greater risk of sunburn. Pole tomato varieties, with an extended crop-bearing season, are more attractive to these insects than other tomato types.
  
  

Monitoring

• Monitor your tomato crop's leaf miner infestation with plastic trays placed randomly beneath the plants. The larvae will drop into the trays as they pupate. Thirty or 40 pupae falling into the trays over three or four days indicate an infestation heavy enough to merit treatment. If you have newly mined leaves but no pupae, the insects' natural predators -- including parasitic wasps -- are keeping the leaf miner populations at harmless levels.
  
  

Tomato Leaf Miner Control

• Select tomato varieties with naturally curling leaves. They have higher resistance to leaf miners. Examine all seedlings before transplanting them; destroy infested plants. Treat heavily infested older plants with a soil drench of Spinosad-based microbial insecticide. Apply the insecticide up to three times over three weeks.