Elevated CO2 has variable effects on plant-insect interactions

Atmospheric CO₂ levels have increased dramatically over the past century. High levels of atmospheric CO₂ can potentially change metabolic processes in plant tissue and influence their interactions with other organisms. Previous studies have shown that elevated CO₂ affects plant defense against different types of herbivores. In general, the jasmonic acid (JA) pathway for defense against chewing herbivores like caterpillars, is inhibited while the salicylic acid (SA) pathway against piercing/sucking herbivores such as aphids, is up-regulated in grains and legume crops at elevated CO₂. We hypothesized that chewing herbivore performance would improve on vegetable crops at elevated CO₂ (e-CO₂). To test this, we raised Solanum lycopersicum plants at ambient (450 ppm) and e-CO₂ conditions (750 ppm). At the 4-leaf stage of tomato growth, we inoculated the plants with neonate larvae of three different moth species (Manduca sexta, Trichoplusia ni and Spodoptera exigua) and allowed them to feed for a week before weighing. Results show that elevated CO₂ had relatively mixed effects on the three species of insects, but the general trend was that caterpillar performance (weight) increased at e-CO₂ for M. sexta which are tomato specialists, but decreased for the other two species. Variation in transcriptional and metabolite responses of plants will be presented.