Thrips are tiny
insects, typically just a millimetre in length. Some are barely half
that size. If that’s how big the adults are, imagine how small a thrips’
egg must be. Now, consider that there are insects that lay their eggs inside the egg of a thrips.
That’s one of them in the image above – the wasp, Megaphragma mymaripenne. It’s pictured next to a Paramecium and an amoeba at the same scale.
Even though both these creatures are made up of a single cell, the wasp
– complete with eyes, brain, wings, muscles, guts and genitals – is
actually smaller. At just 200 micrometres (a fifth of a
millimetre), this wasp is the third smallest insect alive* and a miracle
of miniaturisation.
The wasp has several adaptations for life
at such a small scale. But the most impressive one of all has just been
discovered by Alexey Polilov from Lomonosov Moscow State University,
who has spent many years studying the world’s tiniest insects.
Polilov found that M.mymaripenne has one of the smallest
nervous systems of any insect, consisting of just 7,400 neurons. For
comparison, the common housefly has 340,000 and the honeybee has
850,000. And yet, with a hundred times fewer neurons, the wasp can fly,
search for food, and find the right places to lay its eggs.
On top of that Polilov found that over 95 per cent of the wasps’s
neurons don’t have a nucleus. The nucleus is the command centre of a
cell, the structure that sits in the middle and hoards a precious cache
of DNA. Without it, the neurons shouldn’t be able to replenish their
vital supply of proteins. They shouldn’t work. Until now, intact neurons
without a nucleus have never been described in the wild.
And yet, M.mymaripenne has thousands of them. As it changes
from a larva into an adult, it destroys the majority or its neural
nuclei until just a few hundred are left. The rest burst apart, saving
space inside the adult’s crowded head. But the wasp doesn’t seem to
suffer for this loss. As an adult, it lives for around five days, which
is actually longer than many other bigger wasps. As Zen Faulkes writes,
“It’s possible that the adult life span is short enough that the
nucleus can make all the proteins the neuron needs to function for five
days during the pupal stage.”
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