Results of previous studies on foliage suitability as well as our composite summary suitability rating are given in Table 2. This table lists the scientific names of trees in alphabetical order. Table 3 is an index to common names, and Table 4 is the taxonomic checklist for all species listed in Table 2.
Table 2 generally supports Lechowicz and Maufette's (1986) conclusion that variation in foliage suitability to the gypsy moth is highly related to taxonomic affinity of tree species. Foliage suitability tends to be similar both among congeneric species, and among genera within the same family. For example, feeding trials indicated high foliage suitability for virtually all Quercus species tested to date. Similarity within genera and higher taxonomic groups was the basis for our use of the suitability of closely related tree species to extrapolate the suitability of species for which there is no known information. However, caution should be used in drawing conclusions based on these extrapolations as there often is considerable variation in foliage suitability within the same genus (e.g., Betula), and variation is even greater among genera within the same family (e.g., Pinaceae).
Montgomery (1991) pointed out the difficulty in interpreting the results of gypsy moth feeding trials. Table 2 shows that variation in measurement and interpretation techniques used in the different studies often resulted in contradictory conclusions. Clearly, actual measurements of gypsy moth defoliation levels in the field are more meaningful indicators of hosts suitability. Montgomery also pointed out that there often is considerable variation in foliage suitability within a species.
We expect that more reliable estimates of suitability will become available as additional tests are completed. The feeding trials summarized here are currently constitute the best available information for predicting future effects on these species, but these data should be updated periodically. Definitive measures of foliage suitability will not be available for North American tree species until gypsy moth populations become established in the range of all of these species.