Allium leafminer adult on leek.
The flight is over, but the war may have just begun! The larvae have taken hold and will remain steadfast as pupa through the summer.
The allium leafminer adult spring flight is done for the season! However, the larva and pupa are the now the main concern.
Eggs will hatch within a week of being laid and the larvae begin to mine. As the larvae grow they will begin to mine down the leaves toward the stem of the plant – even mining through leaf layers deeper into the stem for protection and food.
Allium leafminer larva inside mine on wild garlic leaf.
Once the larvae are large enough, about 2-3 weeks of development, they will pupate within plant tissue. We estimate that the majority of the ALM larval population will have completed pupation by the 2nd week of June. At this point the pupa “hibernate” (called aestivation) through the summer months and will hatch as adults at the end of September.
Allium leafminer larval mine in wild garlic.
In the late larval and pupal stages the majority of damage from ALM has already occurred to the plant. We do not know if this pest transmits any diseases but we currently do not believe that ALM does. What ALM does do is open up entryways for pathogens to infect the plant, which can be a major issue for yields.
Allium leafminer pupa within the stem of an onion.
So what can you do? Well, if you mostly have larva, then targeting the larva using some form of control that can penetrate the plant is best method.
If you have more pupa than larva, then treatment for the insect may not be affect due to the decreased metabolism of the pupa. The next best thing to do would be to try and protect your crop from disease and harvest before the adult flight in the fall, destroying all larva and pupa you find.