Wasp
Wasps first appeared in the fossil record in the Jurassic, and diversified into many surviving superfamilies by the Cretaceous. They are a successful and diverse group of insects with tens of thousands of described species; wasps have spread to all parts of the world except for the polar regions. The largest social wasp is the Asian giant hornet, at up to in length; among the largest solitary wasps is a group of species known as tarantula hawks, along with the giant scoliid of Indonesia ("Megascolia procer"). The smallest wasps are solitary chalcid wasps in the family Mymaridae, including the world's smallest known insect, with a body length of only , and the smallest known flying insect, only long.
Trichogramma
Although several groups of egg parasitoids are commonly employed for biological control throughout the world, "Trichogramma" spp. have been the most extensively studied. More than a thousand papers have been published on "Trichogramma" species, and they are the most used biological control agents in the world. "Trichogramma" spp. are unique in approaching the size limit of how small an insect can be, which would be determined by how few neurons they can fit in their central nervous systems, yet exhibiting a complex behavior to sustain their lives. These wasps have less than 10,000 neurons, which is 1/100th that of the next smallest insect.