Two blocks of Scotch pine Christmas trees were inspected to determine an appropriate time to evaluate Zimmerman pine moth damage, and to determine reinfestation rates for trees previously attacked by this insect. Results showed that damage evaluation should be delayed until mid-August and possibly later, in early fall. Evaluation done before this time could result in underestimation of total damage. In the reinfestation study, previously attacked trees were shown to sustain both a higher rate of reattack and more attacks per tree the following year than control trees. However, at most, only 61 % of the new attacks the following year were on trees with a previous attaek. Also, 47% or more of the infested trees observed the second year were newly infested. These results indicate little practical benefit of using attacked trees solely as a trap crop for ovipositing moths. Attacked trees with severe damage should therefore be removed.
Yonker, James W. and Schuder, Donald L.
"Appearance of Damage Symptoms and Reinfestation Rates for Christmas Trees Attacked by the Zimmerman Pine Moth, Dioryctria Zimmermani (Lepidoptera: Pyralidae),"
The Great Lakes Entomologist, vol 20
Available at: https://scholar.valpo.edu/tgle/vol20/iss1/3