Douglas-fir tussock moth (Orgyia pseudotsugata (McDunnough)) larvae were fed foliage obtained from the top and bottom of the crowns of Douglas-fir, grand fir, and subalpine fir under controlled laboratory conditions. High density field populations were simulated by forcing larvae to feed upon old-growth foliage creating a stress factor that was detrimental to the population. The host plant and crown position had a significant effect on frass production, head-capsule size, and pupal weight. The number of eggs produced was significantly greater from foliage obtained from the top of the crown. The most significant factor was whether larvae were forced to feed upon old-growth foliage. This “stress” resulted in increased development time, frass production, number of instars and decreased head capsule size, and egg production.