Growth of Arizona Rose and Attack and Establishment of Gall Wasps Diplolepis fusiformans and D. spinosa (Hymenoptera: Cynipidae)

The two cynipid wasps, Diplolepis fusiformans (Ashmead) and D. spinosa (Ashmead), which induce galls on shoots of Rosa arizonica Rydberg, attack longer, more vigorous shoots with a higher probability than less vigorous shoots. Also, more adult insects emerge per gall on more vigorous shoots including Diplolepis , the cynipid inquiline Periclistus , and parasitoids. This indicates that establishment in galls on vigorous shoots in relation to plant resistance is higher than on less vigorous shoots. However, the presence of Periclistus , which makes multiple chambers per Diplolepis host, complicates an exact interpretation of the relative roles of plant resistance and natural enemies in the survivorship of Diplolepis gallers. As ramets of R. arizonica age, mean shoot length declines, and attacks by Diplolepis are concentrated on young vigorous plants. The patterns of attack and establishment of Diplolepis species are similar to those described for three species of tenthredinid sawfly gallers in the genus Euura . This study therefore contributes to an understanding that some herbivores require vigorous plants for successful use of resources, in contrast to arguments that herbivores survive best on stressed plants.