Hormones of Insects Body
Although hormones are mainly present in chordates, yet some hormones are also present in arthropods, that is insects. There are various hormones secreted in insects, which play role in metamorphosis. Some of the hormones are as follows.
1- Brain hormone (BH)
The brain has neurosecretory cells. Neurosecretory cells of the brain secrete brain hormones. The chemical nature of brain hormone is lipid. These hormones activate corpora cardiaca, which is a part of the retro-cerebral complex of the stomatogastric nervous system.
2- Prothoracicotropic hormone (PTTH)
The corpora cardiaca secrete this hormone, which stimulates the prothoracic glands for secretion. The corpora cardiaca are a pair of neuro-hemal organs, which are located on the walls of the aorta just behind the brain.
3- Prothoracic gland hormone (PGH) / Ecdysone
This hormone is the secretion from the prothoracic gland, by the paired bilateral sheet of cells in the thorax, chemical nature of this hormone is ecdysteroid. This hormone plays role in moulting and metamorphosis in insects. Larva of insects can not metamorphose into the adult in absents of this hormone.
4- Juvenile hormone (JH)
Corpora allata, another component of the retro-cerebral complex, secrete this hormone. Chemically it is non-sterol lipid. This hormone plays role in metamorphosis because it regulates morphogenesis. Hence, play role in the development of larva to pupa, but not larva to adult. Corpora allata gland is located beneath the brain of insects.
Metamorphosis in insect
Structural change in the body, from larva to adult form is called metamorphosis, In other words, we can say that larval change to adult form, which can be seen from Porifera to Chordata. So metamorphosis is also present in insects. Insects display mainly 4 types of metamorphosis.
In this type of development, newly hatched organisms look like their adult, except differ in size and difference in the armature of spines. This means there is no need for metamorphosis, newly hatched organism resembles with their adult but small in size. Example – Silver-fish, Springs-tails.
2-Hemimetabolous development or Incomplete metamorphosis
In this type of development, newly hatched creatures do not completely look like their adult, so there is half metamorphosis needed. Some terrestrial arthropods have aquatic immature stages called nymphs. Which respire by tracheal gills, but their adult respire by trachea. So in this type of metamorphosis immature stages have only changed some systems, such as the tracheal gills system to the tracheal system. There are no complete larva and pupal stages. Example – Dragonflies, Mayflies, etc.
3- Paurometabolous development or Gradual metamorphosis
In this type of metamorphosis, the newly hatched nymph resembles their adult but lacks wings and external genital aperture, growth and development of wings and genital aperture takes place gradually with increasing age. Nymph undergoes several nymphal stages through moulting to become adult. So we can say that no sudden metamorphosis takes place. Example – Gross-hopper, Aphides, Stink.
4- Complete metamorphosis or Holometabolous development
In this type of metamorphosis, all stages are present, egg, larva, pupa, and adult. Larva hatched from the egg, and this larva moults in pupa after some growth and development and later this pupa differentiate into the adult after some growth and development and finally young adult breaks puparium (upper covering of pupa) to come out. Example – Housefly, mosquito, butterfly.
Roles of Insects hormones and Pheromones in biological paste control
Biological paste control is the process of paste control by biological method without the use of harmful chemicals, thus less hazard and harm to the environment. Several biological compounds such as some hormones and pheromones are used in the biological paste control process. Some plants also secrete insect hormones like chemicals to control insect paste, some of these are described here.
1- Role of hormones in biological paste control
During the larval stage corpora allata, pair glands, located beneath the brain of insects, secreted Juvenile hormone. It allows larva-pupa or larva to larva metamorphosis but not to larva to adult metamorphosis. A synthetic compound namely Altosid, acts like the insect’s growth regulator is chemically similar to the juvenile hormone, application of this chemical seizes the development and metamorphosis of the larva into the adult and kills the larva, help in paste control, without harming the environment.
Another insect hormone, ecdysone secreted by prothoracic glands, this hormone induces metamorphosis. In some insects, larva s more harmful but the adult is less harmful or harmless. So ecdysone is very helpful in insect control, some plant leaves produce the ecdysone-like chemical which promotes premature metamorphosis into the adult so harmful larva is eliminated.
2-Pheromones paste control
Pheromones are substances secreted by the exocrine glands and released into the environment and responded to by the animals of some species. Pheromones are mainly secreted for communication between members of the same species. Some pheromones act as sex attractants, secreted by females to attract the male of some species. Chemically synthesized pheromones are used to attract males and traps to kill. Male insects are attracted to chemically synthesized pheromones as they confuse, and go to the location of the source of pheromones, they think it is pheromones from females, and they are trapped into the net and then killed.
References and Sources
- Text Book of Zoology Invertebrates by R.L. Kotpal. 10th edition.
- https://www.scienceirect.com (Insects hormones – an overview | ScienceDirect Topics
- https://www.britannica.com (Insect – Role of hormones | Britannica)
- https://www.studyandscore.com/studymaterial-detail.php?Id=phylum-arthropoda-metamorphosis-in-insects- 3%
- https://www.biologydiscussion.com/invertebrate-zoology/insects/metamorphosis-kinds-events-and-role-of-hormones/33522- 2%
- https://pediaa.com/difference-between-hormones-and-pheromones/- 1%
- https://genent.cals.ncsu.edu/bug-bytes/endocrine-system/- 1%
- https://www.zigya.com/competition/neet/study/Biology/BI/Chemical+Coordination+and+Integration/BIENNT11178352/- 1%
- http://classnotes123.com/metamorphosis-definition-and-types-of-metamorphosis/- 1%