Effect of elevated CO2 levels on the performance of tropical soda apple and its biocontrol agent Gratiana boliviana (Chrysomelidae)

We studied the effect of elevated CO₂ on the performance of the invasive weed, tropical soda apple (Solanum viarum Dunal) and its biocontrol agent Gratiana boliviana Spaeth. We established three levels of CO₂ in environmental growth chambers: ambient, 400 ppm; medium, 580 ppm; and high, 780 ppm. Plants growing at the high level were taller and had greater root and stem biomass compared to those growing at the ambient level. Specific leaf area, leaf water and leaf nitrogen content were highest at medium CO₂, followed by ambient, and high CO₂ level. Gratiana boliviana immature survival and developmental time was negatively affected at high CO₂ but not at medium or ambient levels. Adult fecundity was higher at medium compared to ambient and high CO₂ levels. The implications of rising CO₂ levels on weed biological control are discussed.