Science is always turning up new
and intriguing associations between unexpected partners. Flicking through a
pile of New Scientist magazines the other day, I came across what 1 thought was
a fascinating snippet. It concerned a 67 million year old association between
beewolves and a Streptomyces bacterium. Beewolf wasps are a ' type of solitary
digger wasp. They get their name from the female's habit of catching bees to
feed her developing young. This newly discovered association between beewolves
and Streptomyces is novel in that the beewolves are using the bacteria to
defend themselves from attack by fungi.
The European Beewolf (Philanthus
triangulum) catches a bee, stings it into immobility and then carries it back
and secretes it in an underground brood chamber which she has previously dug in
sandy soil. She may provision the chamber with up to five bees, paralysed, but
unfortunately for them, still alive. These serve as food for the beewolf larva
which emerges from the single egg laid in the chamber before it is sealed.
The practice of keeping the prey
alive until they are almost completely consumed, while gruesome to us and no
doubt exceedingly unpleasant for the prey, has an underlying commonsense
practicality. It means that the beewolf larva has a high quality food source throughout the time that it spends feeding
and growing in the brood chamber, rather than one which is dead and
therefore rapidly rotting and decaying.
Researchers have known for many
years that the female beewolf also smears the ceiling of the brood chamber with
a white gooey mass originating from cavities in her antennae. Although no‑one
knew quite what was in the goo, it appeared to be important to the larval
beewolves, which would smear some of it on to the silk of their cocoons during
pupation. Recent scanning electron microscopy studies have discovered bacteria‑like
structures in special reservoirs in the female beewolves' antennae. These
structures have turned out to be a type of Streptomyces bacterium and genetic
studies have shown it to be a new species.
Streptomyces bacteria are known to
produce antifungal chemicals. (A different kind of Streptomyces is already used
to produce a human antifungal drug called nystatin). Now, the beewolf brood
chamber is warm and humid, which is just the kind of environment fungi love.
Smearing the Streptomyces goo on themselves may therefore be a vital step in
the beewolf life cycle, helping to prevent the pupa from falling prey to fungal
pathogens while immobilised in the cocoon.
To test this theory, 15 beewolf
larvae were deprived of contact with the white bacterial goo, while 18 were
allowed contact. Only one of those deprived of contact lived to adulthood,
while 15 of the 18 others which had contact with the bacterial mass, survived.
This seems a pretty good indication that the Streptomyces bacteria hosted in
the antenna) reservoirs are indeed providing antibiotic fungal defences to the
beewolf pupae.
Alexander Fleming's discovery of
Penicillin in 1928 led to a revolution in our available options for healthcare.
It paved the way for the discovery of a vast range of antibiotics capable of
very simply treating once fatal infections with, by and large, very few side
effects. Having recently had personal cause to be exceedingly grateful for the wonders
of modern antibiotics, 1 can testify to the immense difference they have made
to our medical care. However, it seems that we are way behind the insects,
which have been successfully employing antibiotics produced by other organisms
to improve their life expectancies, not merely for decades, but for millions of
years!
The main reference for this
article is:
Kaltenpoth, M., et al. 2005. Symbiotic bacteria protect wasp larvae from fungal infestation. Current Biology 15 (March 8): 475‑479. Article available at
http://www. current‑biology.com/content/
(the March 8th edition 2005).
You can watch a video of a beewolf female smearing bacteria on the ceiling of its brood chamber at (http:// www.youtube.com/watch?v=wbDdIHsYO3M).