A tiny parasitic wasp that is smaller than some single-cell organisms (such as Paramecium, pictured bottom) has the fewest neurons of any insect studied so far. The bulk of the cells even lose their nuclei when the insects become adults.
Alexey Polilov of Lomonosov Moscow State University sectioned pupae and adults of the wasp (Megaphragma mymaripenne, pictured top) and examined their central nervous systems with light and electron microscopy. The wasp's brain contained around 4,600 neurons — orders of magnitude fewer than house flies (340,000 neurons), bees (850,000) or even closely related parasitic wasps (37,000).
During metamorphosis to an adult, more than 95% of M. mymaripenne's neurons lost their nuclei and cell bodies — the bulbous part of the neuron that contains the nucleus. As a result, the creature's brain shrank by almost 50%. The neurons seem to function without nuclei, because the wasps were still able to fly, eat and find hosts for eggs.
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Wasp neurons lack nuclei. Nature 480, 294 (2011). https://doi.org/10.1038/480294a
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DOI: https://doi.org/10.1038/480294a
