The centriole adjunct of insects: Need to update the definition

• The hypothesis on the origin of the centriole and the centrosome of insects is described.
• The progressive modifications of the sperm structure in Homoptera are enlisted.
• The spermiogenesis of Matsucoccus feytaudi explains the occurrence of a reversal evolution.
• The centriole adjunct of insects is the final step in the post-nuclear storage of material.

The ancestral eukaryotes presumably had an MTOC (microtubule organizing center) which late gave origin to the centriole and the flagellar axoneme.The centrosome of insect early spermatids is in general composed of two components: a single centriole and a cloud of electron-dense pericentriolar material (PCM). During spermiogenesis, the centriole changes its structure and gives rise to a flagellar axoneme, while the proteins of PCM, gamma tubulin in particular, are involved in the production of microtubules for the elongation and shaping of spermatid components. At the end of spermiogenesis, in many insects, additional material is deposited beneath the nucleus to form the centriole adjunct (ca). This material can also extend along the flagellum in two accessory bodies (ab) flanking the axoneme.Among Homoptera Sternorrhyncha, a progressive modification of their sperm flagella until complete disappearance has been verified. In the Archaeococcidae Matsucoccus feytaudi, however, a motile sperm flagellum-like structure is formed by an MTOC activity. This finding gives support to the hypothesis that an evolutionary reversal has occurred in the group and that the cell, when a non-functional centriole is present, activates an ancestral structure, an MTOC, to form a polarized motile bundle of microtubules restoring sperm motility.The presence and extension of the centriole adjunct in the different insect orders is also enlisted.