It is found in apple-growing areas of the northern United States and Canada. The larvae mine the leaves of the apple. About 4 percent of the leaf area is disrupted by each larva. When populations densities are high, severe defoliation occurs. A heavy infestation can cause stunting of the fruit growth, reduced terminal growth, early leaf drop, premature ripening, drop of fruit and reduced fruitset the following season.
Extensive mining combined with drought conditions can worsen plant damage.
Factors Affecting Abundance Parasitism under natural conditions is nearly 100 percent. Birds and predator insects reduce populations. Mortality in winter can be high, especially under conditions of alternate thawing and freezing. In the north central states, this leafminer has three generations per year. Spring-generation adults emerge in late April and continue flying until the middle of June.