''Megaphragma mymaripenne'' is a very small

wasp A wasp is any insect of the narrow-waisted suborder Apocrita of the order Hymenoptera which is neither a bee nor an ant; this excludes the broad-waisted sawflies (Symphyta), which look somewhat like wasps, but are in a separate suborder ...

. At 200

μm The micrometre (Commonwealth English as used by the International Bureau of Weights and Measures; SI symbol: μm) or micrometer (American English), also commonly known by the non-SI term micron, is a unit of length in the International System ...

( mm; inch) in length, it is the third-smallest extant insect, comparable in size to some

single-celled organisms A unicellular organism, also known as a single-celled organism, is an organism that consists of a single cell, unlike a multicellular organism that consists of multiple cells. Organisms fall into two general categories: prokaryotic organisms and ...

. It has a highly reduced

nervous system In biology, the nervous system is the complex system, highly complex part of an animal that coordinates its behavior, actions and sense, sensory information by transmitting action potential, signals to and from different parts of its body. Th ...

, containing only 7,400

neuron A neuron (American English), neurone (British English), or nerve cell, is an membrane potential#Cell excitability, excitable cell (biology), cell that fires electric signals called action potentials across a neural network (biology), neural net ...

s, several orders of magnitude fewer than in larger

insect Insects (from Latin ') are Hexapoda, hexapod invertebrates of the class (biology), class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body (Insect morphology#Head, head, ...

s (for example, a

honey bee A honey bee (also spelled honeybee) is a eusocial flying insect within the genus ''Apis'' of the bee clade, all native to mainland Afro-Eurasia. After bees spread naturally throughout Africa and Eurasia, humans became responsible for the ...

has about 850,000). This is the smallest number of neurons in all insects and flying animals. Its average lifespan in adulthood is 5 days. In January 1920, specimens of an unknown insect were collected in

Hawaii Hawaii ( ; ) is an island U.S. state, state of the United States, in the Pacific Ocean about southwest of the U.S. mainland. One of the two Non-contiguous United States, non-contiguous U.S. states (along with Alaska), it is the only sta ...

associated with

thrips Thrips (Order (biology) , order Thysanoptera) are minute (mostly long or less), slender insects with fringed wings and unique asymmetrical mouthparts. Entomologists have species description , described approximately 7,700 species. They fly on ...

, suspected of being egg parasites. The insects were described as a new species and genus ''Megaphragma mymaripenne'' 1924 by

Philip Hunter Timberlake Philip Hunter Timberlake (1883-1981) was one of the most prolific American entomologists of the 20th century. He was born on June 5, 1883, in Bethel, Maine, and died in 1981 in Riverside, California, where he had served as an Associate Entomologist ...

. ''M. mymaripenne'' specimens were next found on 29 March 1927, again with thrips, on the leaf of a genus ''Croton'' plant. On 10 May 1930, specimens were found near thrips and thrips eggs, and mature

pupae A pupa (; : pupae) is the life stage of some insects undergoing transformation between immature and mature stages. Insects that go through a pupal stage are holometabolous: they go through four distinct stages in their life cycle, the stages th ...

were found inside the thrips eggs. As of 1930, the genus was not thought to be native to Hawaii. Nervous systems are one of the principal factors that limit shrinking body size. The entire

central nervous system The central nervous system (CNS) is the part of the nervous system consisting primarily of the brain, spinal cord and retina. The CNS is so named because the brain integrates the received information and coordinates and influences the activity o ...

forms 6% of the body mass of ''M. mymaripenne'', and the brain makes up 2.9%. Of the wasp's 7,400 neurons, 4,600 are located in the brain. A small insect from other families often deals with the issue of having a large brain in relation to its head size by shifting its brain into its thorax and even abdomen. However, wasps cannot, as to keep their heads flexible, the head's connection to the thorax is relatively limited. Uniquely, by the time ''M. mymaripenne'' reaches adulthood, 95% of its nervous cells have lost their nuclei. Only 339–372 nuclei are found throughout the central nervous system, of which 179–253 are found in the brain. The nervous system of the pupae of ''M. mymaripenne'' makes up 19% of its body mass, 11% of which is the brain. Unlike in adults, cells in the pupae have nuclei. Only in the final stage of development do these undergo

lysis Lysis ( ; from Greek 'loosening') is the breaking down of the membrane of a cell, often by viral, enzymic, or osmotic (that is, "lytic" ) mechanisms that compromise its integrity. A fluid containing the contents of lysed cells is called a ...

, which greatly reduces the volume of the nervous system. While the brains of pupae are 93,600 μm³, those of the adults are only 52,200 μm³. Accompanying this shrinkage of brain volume is a shrinking of the

occipital The occipital bone () is a cranial dermal bone and the main bone of the occiput (back and lower part of the skull). It is trapezoidal in shape and curved on itself like a shallow dish. The occipital bone lies over the occipital lobes of the cere ...

area of the head, with the

cuticle A cuticle (), or cuticula, is any of a variety of tough but flexible, non-mineral outer coverings of an organism, or parts of an organism, that provide protection. Various types of "cuticle" are non- homologous, differing in their origin, structu ...

folding into helical spirals. Researchers believe the wasp can survive without nuclei because of its short lifespan; the proteins manufactured during the

pupa A pupa (; : pupae) is the life stage of some insects undergoing transformation between immature and mature stages. Insects that go through a pupal stage are holometabolous: they go through four distinct stages in their life cycle, the stages th ...

l stage last the animal long enough to complete its life journey. Despite their reduced nervous systems, adult wasps can fly, feed, and locate hosts to lay their eggs. The wasp eggs are deposited in the eggs of

. To emerge, the wasps cut an 80-90 μm near-circular hole in the eggs.

References

{{Taxonbar, from=Q6808804 Trichogrammatidae Insects described in 1924 Taxa named by Philip Hunter Timberlake