The role of leaf resin in the interaction between Eriodictyon californicum (Hydrophyllaceae) and its herbivore, Trirhabda diducta (Chrysomelidae).

The chaparral shrub Eriodictyon californicum secretes a phenolic leaf resin composed of flavonoid aglycones. We used leaves with artificially altered resin contents to test the effects of resin on the feeding, growth, and oviposition of the specialist herbivore Trirhabda diducta. In addition, we compared Trirhabda feeding and growth on young foliage with that on foliage from the preceding year. Our results show that the Eriodictyon leaf resin affects Trirhabda larvae and adults similarly, having no significant effect on growth rates or on nutrient utilization at up to 5X the resin levels normally encountered by larvae in the field. Both Trirhabda larvae and adults respond to high resin concentrations by increasing their consumption rates, with concomitant decreases in digestibility and the efficiency of conversion of ingested food to biomass. Low-resin foliage is preferred by larvae for feeding and by adults for oviposition. Larvae feeding on leaves of the current season have higher growth efficiencies, consumption, and growth compared to larvae feeding on leaves from the preceding year.