Caterpillars and other insect larvae need nitrogen to grow and build new tissues, but adult insects can survive and reproduce on a high carbohydrate diet. So it made sense that more adults would migrate to the high CO2 plants, DeLucia said.
But did the higher sugar levels in the leaves explain the whole effect" To find the answer, the team allowed beetles to live out their lives in one of three conditions: on a high CO2 plant, on a low CO2 plant outside the Soy FACE plot, or on a low CO2 plant grown outside the test plot but which had its sugar content artificially boosted.
What we discovered was startling, DeLucia said.
The beetles on the high CO2 soybean plants lived longer, and as a result produced more offspring, than those living outside the Soy FACE plot. Even those fed a supplemental diet of sugars did not see their life span extended.
So here we were thinking that sugars were the main thing causing the beetles to feed more on these high CO2 leaves, DeLucia said. And that still may be true, but sugars arent whats causing them to live longer and have more breeding events and offspring.
The team turned its attention to the hormonal signaling pathways of the plants, focusing on a key defensive chemical the plants produced to ward off an insect attack. When insects eat their leaves, soybeans and other plants produce a hormone, jasmonic acid, that starts a chain of chemical reactions in the leaves that boost their defenses. Normally this cascade leads to the production of high levels of a compound called a protease inhibitor. When the insects ingest this enzyme, it inhibits their
|Contact: Diana Yates|
University of Illinois at Urbana-Champaign