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

The phenomenon of sex-biased variation in herbivore attack of dioeciou s plants has generated much recent interest among ecologists. In a rec ent study, we discovered that plant sex was an important predictor of densities of a guild of gall-forming sawflies: male clones of arroyo w illow, Salix lasiolepis, supported significantly higher sawfly densiti es than did females. To test the generality of this phenomenon, we her e examine the relationship between willow sex and densities of a diffe rent group of herbivores that includes two leaf-mining lepidopterans, a gall-forming mite, and a gall-forming fly. In contrast to our earlie r 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 d ensity. These results imply that some factors that strongly affect the abundance of one set of herbivores may have little relevance to a dif ferent set of herbivores attacking the same host, suggesting that the development of a general theory of sex-biased herbivory may require nu merous and varied case studies.