Insect damage to second-year cones was generally not significantly different between crown levels, but was significantly different among areas and among trees within areas for Conophthorus, Megastigmus, and Cydia. Both cone length and width were not significantly different between lower and middle crown, but cone length was significantly greater in the upper crown. Seeds per cone ranged from 34 to 66, but the percent of sound seed per cone varied significantly according to the amount of insect damage.
Schmid, J. M.; Mitchell, J. C.; Carlin, K. D.; and Wagner, M. R.
"Insect damage, cone dimensions, and seed production in crown levels of ponderosa pine,"
Great Basin Naturalist: Vol. 44
, Article 5.
Available at: https://scholarsarchive.byu.edu/gbn/vol44/iss4/5