• Thomas, A.W.
  Forestry Canada
  

The effects of tree species, shoot age, and sex of larvae on food consumption and utilization were investigated in a factorial experiment. Diets prepared from lyophilized and powdered current-year shoots, from two age classes (sample dates) of Picea glauca (Moench) Voss, Picea rubra Sarg., and Pícea mariana (Mill.) B.S.P., were evaluated for eight performance criteria. All factors had significant effects on all criteria except for tree species on assimilation effrciency, shoot age on development time, and sex on net growth efÏiciency. Eight of the possible 24 two-factor interactions and one of the possible eight three-factor interactions were significant. Food utilization efftciencies and relative growth rate were in the low and moderate characterization limits for immature arthropods; relative consumption rates were high. The higher performance values on Picea glauca were related to this species greater vulnerability to spruce budworm. Performance criteria of similar larvae on an artificial diet were compared with those on the foliage-diets.