Impact of temperature on defensive chemistry of the invasive weed Echium plantagineum and implications for its biological control under climatic warming

Experiments were conducted under controlled environmental conditions to assess the impact of temperature on the production of secondary compounds by Echium plantagineum, a widespread invasive weed in Australia.  Plants were grown for 4 weeks under typical field conditions (25C daytime/18C nighttime), and then transferred to cooler (20C/15C) or warmer (25C/15C and 35C/25C) conditions.  After 4 weeks in the regulated temperatures, plants were harvested and assayed for the abundance of pyrrolizidine alkaloids (PAs) in the foliage.  Plants grown in cooler conditions had elevated levels of total PAs, but plants grown in the warmest conditions showed nearly twice the increase in total PAs.  These results suggest that stress increases the production of defensive compounds by E. plantagineum, and that global warming might have significant impact on the ability of insect herbivores (e.g. weed biocontrol agents) to suppress populations of the weed.