Carnivorous plants inhabit nutrient-poor environments, and they supplement nutrient uptake by capturing and absorbing nutrients from prey, such as insects. Like other plants, carnivorous plants are subject to loss of nutrient-containing tissues to herbivores. Because they occur in low-nutrient environments, tissue loss to herbivory can be expected to have a particularly strong negative effect on carnivorous plants. However, herbivory in carnivorous plants has not been well studied. In this study, we quantified tissue and nutrient losses sustained from herbivory by larvae of the specialist noctuid, Exyra semicrocea, in a population of pitcher plants, Sarracenia alata. We conducted field surveys, analyses of areal foliar damage, nutrient analyses, and feeding trials.
In the study population, 83% (0.83 ± 0.033) (mean ± SE) of pitchers were damaged by E. semicrocea (surveyed in June & September). On average, 15% of each pitcher was consumed. Mean foliar nitrogen concentration was 1.19%, resulting in a mean nitrogen loss to consumption of 0.24 ± 0.041 mg per pitcher (N = 40). Mean foliar phosphorus concentration was 0.044%, resulting in a mean phosphorus loss per pitcher of 0.0086 ± 0.0015 mg (N = 37). Exyra preferentially fed on upper-pitcher ‘waxy’ tissue (25% of waxy tissue damaged) rather than mid-pitcher ‘hairy’ tissue (4.0% of hairy tissue damaged). In preliminary feeding trials, 4th and 5th instar larvae consumed 5.6 ± 0.016 cm2 /day and 6.7 ± 1.4 cm2 /day, respectively. Exyra larvae were observed moving among pitchers. Based on consumption rates, estimated mean time spent feeding on a single pitcher was 2.8 ± 0.19 days (N = 95). Current studies are evaluating the impact of herbivory on the fitness of these plants.