Plants defend themselves against insects by inducing'leaky bowel syndrome

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Plants defend themselves against insects by inducing'leaky bowel syndrome

According to researchers at Penn State, plants can induce "leaky bowel syndrome", the permeability of bowel insects, as part of a multi-pronged strategy to protect against consumption. By improving our understanding of plant defences, these discoveries could contribute to the development of new pest management methods.

"We have discovered that a combination of physical and chemical defences in corn plants can disrupt the intestinal protective barriers of fall legionnaires, creating opportunities for intestinal microbes to invade their body cavities," explains Charles Mason, postdoctoral researcher in entomology. "This can cause sepsis, which can kill the insect, or simply trigger an immune response, which can weaken the insect."

The researchers raised fall legionnaires in the laboratory and inoculated them with one of three types of natural intestinal bacteria. They fed the insects with one of three types of corn known to express enzymes that produce perforations in the intestinal walls of insects; a corn that is characterized by many elongated trichomes, or fine hairs that appear on the surface of the plant and help defend itself from herbivores; and a corn that contains only a few short trichomes. The team used scanning electron microscopy to assess the impacts of various types of bacteria and corn on the integrity of the intestines of fall legionnaires.

Scientists found that the presence of all three types of intestinal bacteria reduced the ability of fall armyworm larvae to damage maize plants, especially when other defences - such as elongated trichomes and enzymes, which can perforate the intestinal walls - were present. However, the species of intestinal bacteria varied to the extent that they weakened insects. The results will be published in the July 22nd issue of the Proceedings of the National Academy of Sciences.

Trichomes, or fine hairs that appear on the surface of the plant, can tear the intestinal walls of insects. Credit: Charles Mason, Penn State
"Our results reveal a mechanism by which some plants use the intestinal microbiota of insects against them in collaboration with their own defenses," explains Mr. Mason.

Gary Felton, Professor and Head of the Department of Entomology, noted that the results should be of great importance in understanding the ecological function of plant defences.

"In the context of our study, disparate plant defences, such as leaf trichomes and plant enzymes, all require certain intestinal microbes for optimal defence against herbivores," he said. "Our results predict that the variation in the effectiveness of plant defences in nature may be, in large part, due to the variability observed in the microbial communities of insect intestines."

A perforation in the intestinal wall of an autumn legionnaire. Credit: Charles Mason, Penn State
The team said the results could help inform the development of insect-resistant crops.

"It may be advantageous to stack the defences of plants that target the insect's intestine to create a'leaking intestine' that exposes the insect to microbial attacks on its immune system," says Mason.