A glimpse of changes to come: effects of elevated CO2 on a tri-trophic system

The earth’s climate is changing at a rapid rate, in part due to increases in CO₂ emissions from industrialization.  Changes in atmospheric CO₂ will undoubtedly impact plants, herbivores, and natural enemies, thus affecting control and impact of herbivorous pests.  The effects of elevated CO₂ on a tri-trophic system involving black mustard (Brassica nigra), cabbage looper (Trichoplusia ni), and the parasitoid (Copidosoma floridanum) were examined in a greenhouse experiment.  Carbon dioxide was injected into a greenhouse bay to average 750 ppm of daytime CO₂, an atmospheric level of CO₂ that is expected in the in the next century.  A second greenhouse bay was kept between 300-600 ppm of CO2, which are modern day levels of ambient CO₂.  A total of 351 mustard plants from three different European populations were placed in one of three herbivore treatments: control (no herbivore), five unparasitized cabbage loopers, or five C. floridanum parasitized cabbage loopers.  Plant chemistry profiles were determined from leaf disc samples taken prior to inoculation with caterpillars and after caterpillars had pupated.  The effects of herbivory and elevated CO₂ on plant fitness were measured by counting and weighing the total number of seeds from each plant while effects on herbivores were measure by pupal wet weight.  The results of this study illustrate the impacts of elevated atmospheric CO₂ on herbivorous pests and their effects on plants.  Data on the effects of elevated CO₂ on parasitoid success offer insight into changes in natural enemy efficacy for future control of pest herbivores.