Murderous Fungi Feed Their Insect Victims to Plants

June 21, 2012
Sara Reardon
http://www.newscientist.com/article/dn21965-murderous-fungi-feed-their-insect-victims-to-plants.html

Summary: Most plants rely on the fungi and bacteria that live in their roots to capture nitrogen decaying organic matter in the soil, since plants themselves cannot directly capture the necessary nitrogen in the air or soil. These fungi include Metarhizium, which live on every continent and colonize most types of plants. The fungi also infect and kill many insect species. By releasing enzymes that eat their way through an insect's outer shell, the fungi slowly takes over the host and kills it from the inside. Micheal Bidochka of Brock University of Saint Catherine's, Ontario, Canada and his team wondered whether there was a link between the insect killing and the plant feeding. After injecting a labeled form of nitrogen into a wax moth larvae called Galleria mellonella, they infected them with Metarhizium fungi. The researchers then buried the larvae in the soil with either beans named Phaseolus vulgaris or switchgrass plants called Panicum virgatum. They placed a screen with pores too small for plant roots to penetrate but large enough for the fungi to cross through between the infected insects and the plants' roots. After 14 days, the insects were dead, and the researchers found their labeled nitrogen in the plants' tissues. It made up 28 percent of the nitrogen in the beans and 32 percent in the switch grass. Insects that had not been infected by the fungi did not transfer any of their nitrogen to the plants after they died. Raymond Saint Leger, an entomologist at the University of Maryland in College Park, says that researchers should find out how widespread the phenomenon is in nature, and whether plants living in natural environments are as dependent on insects as a nitrogen source as the plants in the lab seemed to be.

Relevance: This relates to our previous unit about microbes and fungi. The article discusses the fungi Metarhizium and how it provides nitrogen to the plants, and in class we discussed the nitrogen cycle and how it relates to bacteria and fungi. The fungi capture can capture nitrogen from decaying matter in the soil. Another class topic was symbiosis and symbiotic relationships. In this case, the fungi transfer the nitrogen from the insects to the plant, and the plant provides a home in its roots for the fungi to live. This means it is a mutualistic relationship.