Life cycle of insects


July 5, 2022

The life cycle of insects occurs with metamorphosis and has an epimorphic character - a larva with all segments emerges from the egg, which is more or less different from the adult - the imago. There are two main types of metamorphosis — incomplete and complete transformation. With incomplete transformation, or hemimetabolism, the insect goes through the following phases of development: egg, larva, imago. The egg hatches into a larva, outwardly similar to an adult. It has faceted eyes, the same oral apparatus as in adults, and in older stages - the outer rudiments of wings. Examples are locusts, bed bugs, etc. With complete transformation, or holometabolism, insects go through the following phases: egg, larva, pupa, imago. A larva emerges from the egg, which differs sharply from the imago in the greater homonomy of metamerism, the absence of external wing rudiments, and the weaker development of sense organs. As an example, you can take a May beetle, a scoop, a housefly, a beet weevil, etc.

Embryonic development

Insect eggs are rich in yolk, which occupies the entire central part of the egg. That is why crushing in them is partial, superficial; as a result, a surface layer of identical cells is formed — the blastoderm, which covers the central mass of the yolk. On the future ventral side of the embryo, blastoderm cells begin to divide more intensively, the blastoderm thickens. This area is called the germ line. Later, most of the embryo is formed at its expense. In the germ line, gastrulation occurs (most often by intussusception or epiboly), and initially only two germ layers are formed: ectoderm and mesoderm. The ectoderm gives rise to the outer coverings of the body, the trachea, the nervous system, the genital ducts, the anterior and posterior parts of the intestine, which arise as folds of the coverings at the anterior and posterior ends of the embryo. Musculature, fat body, heart with aorta, hemocytes are formed from the mesoderm. Mesoderm is also involved in the development of the reproductive system. The germ, as a rule, separates much earlier from other tissues in the form of a paired group of cells near the posterior end of the embryo. The endoderm, from which the midgut originates, can be built in two ways in various insects: or due to the nuclei remaining in the thickness