Increased seed consumption by biological control weevil tempers positive CO₂ effect on invasive plant (Centaurea diffusa) fitness

Authors

Justin L. Reeves, USDA-ARS
Dana M. Blumenthal, USDA-ARSFollow
Julie A. Kray, USDA-ARSFollow
Justin D. Derner, USDA-ARSFollow

Date of this Version

2015

Citation

Biological Control 84 (2015) 36–43

Comments

U.S. Government Work

Abstract

Predicted increases in atmospheric CO₂ and temperature may benefit some invasive plants, increasing the need for effective invasive plant management. Biological control can be an effective means of managing invasive plants, but the anticipated range in responses of plant–insect interactions to climate change make it difficult to predict how effective biological control will be in the future. Field experiments that manipulate climate within biological control systems could improve predictive power, but are challenging to implement and therefore rare to date. Here, we show that free air CO₂ enrichment in the field increased the fitness of Centaurea diffusa Lam., a problematic invader in much of the western United States. However, CO₂ enrichment also increased the impact of the biological control agent Larinus minutus (Coleoptera: Curculionidae) on C. diffusa fitness. C. diffusa plants flowered earlier and seed heads developed faster with both elevated CO₂ and increased temperature. Natural dispersal of L. minutus into the experimental plots provided a unique opportunity to examine weevil preference for and effects on C. diffusa grown under the different climate change treatments. Elevated CO₂ increased both the proportion of seed heads infested by L. minutus and, correspondingly, the amount of seed removed by weevils. Warming had no detectable effect on weevil utilization of plants. Higher weevil densities on elevated CO₂ plants reduced, but did not eliminate, the positive effects of CO₂ on C. diffusa fitness. Correlations between plant development time and weevil infestation suggest that climate change increased weevil infestation by hastening plant phenology. Phenological mismatches are anticipated with climate change in many plant–insect systems, but in the case of L. minutus and C. diffusa in mixed-grass prairie, a better phenological match may make the biological control agent more effective as CO₂ levels rise.