A species of fungus-farming beetle that's been hitching rides on wooden shipping pallets has become a serious pest in some areas, killing avocados, poplars and oaks worldwide. The beetles, which only live in dead wood in their native areas, sometimes start attacking living trees when they arrive in a new environment. And that may be because they're mis-smelling the new trees, mistaking living for dead wood.

Researchers at North Carolina State University found that 12 species of ambrosia beetle were creating problems, but there are 3,500 species of the beetle in the world, says Jiri Hulcr, a biologist and one of the researchers, said in a release.

In their paper, published online this week in the Proceedings of the Royal Society B, they write:

The good news is that such probabilities are relatively low for any given introduction event; — the bad news is that the world's tropical and subtropical forests harbour thousands of fungal species associated with thousands of insect species. Even if a small percentage of those have the necessary attributes for killing naive trees, it may result in large numbers of catastrophic outbreaks.

The ambrosia beetles tunnel into trees, then use the chambers they create to grow the fungal crops they eat. In their native habitats they only target dead wood, but once in a new environment that can shift.

One theory as to why they target living trees in new environment is "an 'olfactory mismatch' in the insect whereby a subset of live trees is perceived as dead and suitable for colonization," the paper says.

The fungus they farm triggers an immune response in the tree, causing it to cut off its own water supply to try to kill the fungus, but also killing the tree. It's the same type of scenario that wiped out Dutch elm trees in North America and Europe, Hulcr notes. Dutch elm disease is caused by a fungus that is spread by beetles.

When the redbay ambrosia beetle from southeast Asia arrived in the southeast United States, it began to colonize living redbay and avocado trees – threatening Florida's avocado industry. Non-native ambrosia beetle species have also attacked oak trees in Japan; poplars in Argentina and Italy; and other tree species in Korea, Israel, Thailand and the United States.

It could be the beginning of the end or the end of the beginning, Hulcr said in a release. "The worst of these invasions may be over. It is possible that the strong invasive species have already done all they can do. On the other hand, this may be the first wave of what could be an avalanche of these invasive ambrosia beetles entering new environments and attacking new species. We just don't know yet."

Many of them were transported to their new homes in the wood of wooden shipping pallets, which typically aren't fumigated to kill pests.