How a Brain Hormone Controls Insect Metamorphosis

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Metamorphism simply refers to a ‘change’ and in relation to an insect, the term refers to the changes that take place during the insects’ life cycle that ultimately results in the ‘reproductive’ or the ‘adult’ form of the insect. Although the scientists were aware that a hormone known as PTTH controls the metamorphism of an insect, until few years back, they were clueless about the potential signal pathway that allowed the brain hormone to communicate with the necessary endocrine organs. However, after a team of scientists from the University of Minnesota uncovered the elusive pathway and paved the way to an explosion in the field of agriculture and biological research, more scientific evidence were gained on how a brain hormone controls insect metamorphism at various stages of its lifecycle.

The signaling pathway

The paper with regard to the discovery of the signaling pathway, which is responsible for the insect metamorphism, was published in the December issue of the ‘Science’ journal. According to its lead author, it was the inability to understand the signal pathway that made further research nearly impossible in the field of insect metamorphism. However, following the discovery, scientists are now able to correlate different stages of the programmed metamorphism of insects with the body size and with various environmental and developmental cues. As a result, they are in a better position to uncover safer ways of controlling agricultural pests, as well as insects that carry pathological organisms harmful to the humans.

Regulated genes

However, the recognition of the signaling system is only one aspect of an ever-evolving research field of insect physiology. Based on the findings with regard to the signaling pathways correlating with the insect metamorphism, scientists were trying to unravel the mystery of how the same signaling process could in one instance give rise to a larval form and in another instance give rise to an adult form during the metamorphic process. A group of scientists from the University of Massachusetts Medical School seems to have broken the deadlock by recognizing a certain gene, expressed only in the pupal state, that redirects signaling systems. It can activate a different set of target genes with each metamorphic stage. This gene seems to be regulated by a steroid hormone similar in manner to the changes taking place during puberty in human development.

Two switch’ theory

The same set of researchers who suggested a possible gene based regulatory mechanism for different metamorphic stages has described a ‘two witch’ theory, which roughly correlates with having two types of genes that work in collaboration to let the target genes know when and where to activate. The two genes recognized are named as E93 and EGFR and according to the researchers, the E93 tells the target genes when to turn on and the EGFR tells the same genes where to turn on. This ensures that the signaling pathway acts only at the right time and at the right place during the metamorphism of the insect.


When looking at the ongoing research, it is apparent that insect physiology related to metamorphism is a complex area, which requires further research. Therefore, in years to come, scientists will be able to expand their knowledge with regard to how brain hormones control insect metamorphism. Such understanding will be the basis for useful research in relation to certain aspects of human physiology as well.

More about this author: Dr Pandula Siribaddana

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