Evolution of holometaboly revealed by developmental transformation of internal thoracic structures in a green lacewing Chrysopa pallens (Neuroptera: Chrysopidae).

Abstract

Despite extensive studies on the morphology of holometabolous insects and their larvae, the morphological transformations of internal structures during metamorphosis have been rarely documented. Here, we used micro-computed tomography to investigate the developmental transformations of thoracic structures in the green lacewing Chrysopa pallens (Rambur, 1838) (Neuroptera: Chrysopidae), with emphasis on the development of the digestive, tracheal, and thoracic skeleto-muscular system. All the adult organs were modified during the prepupal or early pupal stage. The histolysis and remodeling began with the skeletal elements, followed by changes in the digestive system before it concluded with modifications of the musculature. Similar to the tracheal system's development, the digestive system did not disappear completely throughout metamorphosis but underwent a dramatic morphological change, which included the midgut significantly decreasing in size during the pupal stage. Our results provide important evidence for understanding the evolutionary pattern of developmental transformations in different major lineages of Holometabola.