Apple trees grown in the eastern United States are subject to attack by several insects and mites that feed on foliage. While injury caused by foliage feeding pests may vary due to the time and type of feeding, the principal mechanism of damage appears to be the reduction of photosynthesis by leaves. If individual pests affect the apple tree via reductions in leaf photosynthesis, it is reasonable to hypothesize that the influence of multiple pests is an additive reduction in leaf photosynthesis. Affirming the additive affect of multiple sources of pest injury would bolster current pest management practices. Spotted Tentiform Leafminer (STLM) (Phyllonorychter blancardella) is an important apple insect pest. Larvae burrow beneath the layers of apple leaves and consume the mesophyll creating mines where most of the green tissue has been removed. Unfortunately, little is known about the influence of damage by this insect on apple tree photosynthesis. Here, we present results from experiments designed to answer three questions: 1. What is the relationship between STLM damage on a leaf and photosynthesis by the leaf? 2. What is the relationship between STLM damage and photosynthesis by the entire tree canopy? 3. Can STLM damage be simulated?