Beetles use an antibiotic new to science to protect their fungal food stores from attack by other fungal invaders. That's according to a new study published this week in the journal Science by a team of researchers led by Jarrod Scott from the University of Wisconsin Madison.
Southern pine beetles are a major pest in the southern United States where they infest pine trees and cause millions of pounds of damage. The adult beetles dig tunnels under the bark of pine trees, and infest them with a particular strain of fungi, called Entomocorticium, which they carry in a special pouch called a mycanjium. The beetles then harvest the fungus to feed to their growing larvae.
It was already known that the Entomocorticium fungus the beetles carefully farm can be outcompeted by another fungus called Ophiostoma, which disrupts the development of young beetles because they don't have enough food. What Scott and his team have discovered is that the beetles play host to two types of bacteria that produce antibiotics which keeps the invading fungus at bay, but which leave the beneficial food fungus alone.
Using a scanning electron microscope they scrutinised the beetles and their homes and it was noticed that the tunnels dug by the beetles in the pine bark were filled with a type of bacteria called actino-bacteria that no-one had noticed before. The researchers also found the bacteria inside the mycanjium pouches of the adult beetles, where they carry the food fungi. They tested the effects of the bacteria and showed that the invading fungus is 20 times more susceptible to it than the food fungus.
This is the first time that beetle has been shown to seek out the help of not just the food fungus but also the bacteria to protect it. Back in 2006, leaf cutter ants were discovered to do something very similar, using home-made antibiotics to protect the colonies of fungus that grow on leaf clippings inside their nests. Future research targeting the bacteria and antibiotics used by the Southern Pine Beetles could provide a brand new way of dealing with the pest beetle and others like it.