Why These Bees May Be Killing the Plants They Feed From

In 2010, Australia was invaded. Myrtle rust, a fungal disease characterized by its yellow-brown spores, descended on the island continent and spread rapidly, threatening up to 17 percent of Australia’s natural flora. Now, new research published in NeoBiota discovered that the fungus could receive help from another introduced species: the western honeybee. If so, this dynamic could be a striking example of “invasive mutualism” in which two non-native species team up to help each other thrive in a new environment.

Earlier field observers noted that bees actively foraged from rust-infected flowers, apparently wrapping the spores around their legs, much like pollen, and sending the infected loot back to the hive. So bees, which were introduced to Australia to act as commercial pollinators, could now be disease vectors.

To find out for sure, biologists from Australia and New Zealand established colonies in known myrtle rust infestation sites. About half of the bees returned to the colony with myrtle rust spores clinging to their bodies, and 45 percent of the pollen storage cells contained inside were contaminated with spores.

But could bees really be feeding on rust spores?

Read more: “Invasive species”

Analysis of the chemical composition of rust spores revealed that they were very nutritious and contained enough protein to feed a colony, as well as all 10 essential amino acids.

Of course, just because rust spores contain so many things that growing bees need doesn’t mean they’re an adequate substitute for good old pollen. So the team collected bee larvae and raised them on a diet strictly of myrtle rust spores. The spore-eating larvae behaved as well as those raised on kiwi and willow pollen, their natural food. “These results suggest that spore foraging may not be an aberration, but a viable foraging strategy for honey bees,” they wrote.

Sip.

Even more alarming, the team found that myrtle rust spores in the colony remained infectious for up to nine days. Commercial hives are regularly transported long distances, in a process that can take between three and seven days. In other words, myrtle rust may not only be getting help from bees, it might also be getting help from humans who traffic in bees.

Once again: swallow.

Researchers warn that this dynamic – bees carrying spores, feeding on them and potentially spreading them to other plants – could become a devastating feedback loop. Although the spores are nutritious, they do not replace pollen in the long term. If bees are indeed vectors of myrtle rust to the plants on which they feed, they may be sowing the spores of their own destruction.

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Main image: Geoff S Pegg.