• Heller, R.C.
  Bureau of Entomology and Plant Quarantine
  
• Bean, J.L.
  USDA Forest Service
  
• Marsh, J.W.
  Maine Forest Service
  

First use of the airplane for surveying forest insect damage was in 1923, when F. C. Craighead made aerial observations of defoliation by the spruce budworm, Choristoneura fumiferana (Clem.), from an open-cockpit seaplane over heavily infested Canadian timber. Craighead found that he could distinguish defoliated timber by the grayish appearance of the terminal branches.