Insect eat more plants in high CO2 environment

The concentration of atmospheric carbon dioxide is increasing at an alarming rate, and a new study has shown that soybean defenses decrease as CO2 increases. It is reported that high concentrations of CO ₂ weaken the main factor in plant defense against leaf-eating beetles. University of Illinois research is published online in the Proceedings of the National Academy of Sciences.

Professor Evan DeLucia, head of the botanical department and author of the study, said burning fossil fuels has significantly increased carbon dioxide levels since the end of the 18th century.

'At present, CO ₂ in the air accounts for about 380 parts per million,' DeLucia said. 'At the beginning of the Industrial Revolution, this ratio was about 280 per million, and it has remained that way for at least 600,000 years - probably millions of years ago.'

DeLucia added that atmospheric carbon dioxide is expected to reach 550 per million by 2050, and that India's rapid industrialization as well as China could accelerate this process.

Scientists have found that plants' defenses decrease as carbon dioxide levels rise.Soybeans in environments with high CO ₂ concentrations attract more mature Japanese beetles than those that grow in areas with carbon dioxide concentrations in normal air. (Photo: Evan Delucia)

The new study, directed by entomology professor and head of the May Berenbuam department, uses outdoor facilities for soybeans in Illinois. This outdoor laboratory can put soybean plants in environments with concentrations of CO ₂ and ozone like in the air without isolating them from other environmental factors such as rain, sunlight, and thunder. coincide.

High concentrations of carbon dioxide accelerate photosynthesis. It also increases the carbohydrate content compared to nitrogen in the leaves. Researchers want to know how the change in the ratio of carbon to nitrogen affects insects that eat plant leaves. They predict that insects eat more leaves to ensure that they have enough nitrogen.

When soybean plants were introduced into the environment with high levels of carbon dioxide, the researchers found the expected effect: Soybean plants in experimental plots have more signs of insect damage than plants. soybeans in nearby areas. On closer inspection, it can be seen that soybean plants in a high CO ₂ environment attracted more Japanese beetles, Western rootworms and more Asian aphids than soybeans in other plots.

Caterpillars and many other insect larvae need nitrogen to grow and create new tissues, however adult insects can survive and reproduce with a high carbohydrate diet. Delucia says this explains how many adult bugs migrate to plants in high concentrations of CO ₂ .

But is the higher sugar in the leaves explaining this whole effect? To find the answer, the team for beetles lives in one of three conditions: high CO ₂ area, low CO ₂ area outside the outdoor laboratory area, and low CO ₂ area outside the experimental land and there is an increase in sugar.

'What we discovered was amazing,' DeLucia said. The beetles in the high CO ₂ area live longer and therefore have more descendants, than the bugs that live outside the experimental area. Even those who have added sugar do not have a longer life.

'We thought that sugar was the main factor that caused the beetles to eat more leaves in high CO ₂ environments,' DeLucia said. 'And this may still be true, but sugar is not a factor that makes them live longer and have more chances to reproduce'.

The team turned their attention to the hormonal signals of plants, focusing on the plant's chemical defense to avoid insect attacks. When insects eat leaves, soybeans and other plants produce a type of hormone, jasmonic acid , to create a series of leaf chemical reactions that enhance defense. Often this leads to the creation of a large amount of a compound called a protease inhibitor. When insects feed on this enzyme, it inhibits their digestibility.

'We discovered that the leaves that grow in high CO ₂ environments lose the ability to produce jasmonic acid, and that self-defense stops working,' Delucia explained. 'The leaves are therefore not fully protected'. Higher amounts of carbohydrates and the absence of chemical defenses have allowed adult insects to have more food, live longer and reproduce more.

'This study demonstrates that global environmental change is multifaceted,' Berenbaum said. 'The impact of high levels of carbon dioxide on plant reactivity to insect damage is exacerbated by the presence of vermin pests in soybean growing areas. Japanese beetles, as the name suggests, are a new species that appears in Illonis. They cause significant damage to soybeans, but the researchers say their potential harm will not increase over time. '

Researchers, both members of the Genetic Biology Council, will find ways to determine whether this process takes place in other tree species.