1/1/2024 0 Comments Stages of metamorphosisIn holometabolous metamorphosis, the changes from one stage to another are more dramatic-egg to larva to pupa to adult-and the larval stages have no physical resemblance to the adult stages, although there are changes akin to incomplete metamorphosis when one larval instar moults to the next. At each stage, the nymph increasingly resembles the final adult form, but even the least developed nymphs, which hatch from the eggs, are of the general adult form. In hemimetabolous metamorphosis, the insect transforms to an adult by passing through a number of nymphal stages, shedding the exoskeleton during a moult between each stage. The two major forms of insect metamorphosis are hemimetaboly (incomplete or partial metamorphosis) and holometaboly (complete metamorphosis). This article is part of the theme issue ‘The evolution of complete metamorphosis’. This review focusses on visualizing the intra-puparial holometabolous metamorphosis of cyclorraphous flies (Diptera), including the primary model organism for all genetic investigations, Drosophila melanogaster, and the blow flies of medical, veterinary and forensic importance, but also discusses similar studies on other insect orders. They can also be applied in some cases to visualize metamorphosis in vivo, including the periods of most rapid and dramatic morphological change. A major advantage of these techniques is that they are rapid and non-destructive, enabling virtual dissection of an organism in any plane by anyone who has access to the image files and the necessary software. These include micro-computed tomography, magnetic resonance imaging and optical coherence tomography. However, advances in imaging technologies developed mainly for medical sciences have been applied to studies of insect metamorphosis over the past couple of decades. However, it can be difficult to visualize the dramatic changes that occur during holometaboly without destructive sampling, traditionally through histology. Metamorphosis and, in particular, holometaboly, the development of organisms through a series of discrete stages (egg, larva, pupa, adult) that hardly resemble one another but are finely adapted to specific roles in the life cycle of the organism, has fascinated and mystified humans throughout history.
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