Short-rotation woody crops (SRWC) are being developed as a sustainable system that simultaneously produces a renewable feedstock for bioenergy and bioproducts and a suite of environmental and rural development benefits. However, damage from defoliating insects can significantly reduce the yield of SRWC and negatively impact their sustainability. Information regarding the relative resistance to defoliation of different SRWC clones is not only useful for deployment and breeding choices, but can also help elucidate ecological patterns of herbivore specialization. Laboratory feeding bioassays tested the resistance of 19 willow (Salix spp.) and six poplar (Populus spp.) biomass production clones to feeding by seven common folivorous insects. Defoliation was measured using a leaf area meter and results were standardized according to leaf area consumed per insect per day. Significant differences in resistance were found among clones (p ≤ .05). The most folivore-resistant groups included the six poplar clones and willow clones SH3, SP3, S546 and S625. Willow clones with S. eriocephala or S. dasyclados parentage were generally less resistant to herbivory than those with other parentages. Comparisons of univariate and multivariate approaches found that the multivariate techniques are robust and conservative, and provide an efficient means of screening a large number of clones in a development program. The multivariate approach provided a clearer sorting of folivores along a continuum of insect specialization. Such sorting may be useful in selecting model folivores to use in tree genetic improvement screening systems to efficiently reveal which clones are more likely to be resistant to multiple insect pests.