SEX-BIASED HERBIVORY IN ARROYO WILLOW - ARE THERE GENERAL PATTERNS AMONG HERBIVORES

The phenomenon of sex-biased variation in herbivore attack of dioecious plants has generated much recent interest among ecologists. In a recent study, we discovered that plant sex was an important predictor of densities of a guild of gall-forming sawflies: male clones of arroyo willow, Salix lasiolepis, supported significantly higher sawfly densities than did females. To test the generality of this phenomenon, we here examine the relationship between willow sex and densities of a different group of herbivores that includes two leaf-mining lepidopterans, a gall-forming mite, and a gall-forming fly. In contrast to our earlier findings, there was no relationship between plant sex and herbivore densities. Consistent with our previous study, both environment (year) and plant genotype (clone) exerted significant effects on herbivore density. These results imply that some factors that strongly affect the abundance of one set of herbivores may have little relevance to a different set of herbivores attacking the same host, suggesting that the development of a general theory of sex-biased herbivory may require numerous and varied case studies.