In general, the weapons and decorations of animals and insects vary according to body size.While it grows larger in large individuals, it usually becomes obstructive and requires more maintenance energy, so it becomes smaller in small individuals with poor nutritional conditions during the growing season.On the other hand, the organs essential for survival and reproduction are secured to have an almost constant size regardless of the body size.

　Insulin and insulin-like growth factors that control blood glucose levels, metabolism, and cell growth and division according to nutritional conditions are attracting attention as one of the mechanisms by which only a part of the body has high nutritional responsiveness. It is a peptide hormone (insulin-like peptide, ILP).

　Recent genomic studies have shown that insects have diverse ILPs depending on the species, and it has been pointed out that each peptide may have a "role division".Although its function is largely unknown, the researchers considered that a specific ILP controls the weapon size of insects, and conducted a genome analysis of the beetle "Red Flour Beetle" that fights with a large jaw as a weapon.

　As a result, it was found that the red flour beetle has five types of ILP (ILP5-1), and one of them, ILP5, was found to be produced according to the nutritional conditions of the larvae.Furthermore, when the expression of the ILP1 gene was suppressed, the large jaw became less than half the normal size, and the growth of the large jaw according to the nutritional conditions disappeared.From this, it was considered that ILP2 acts as a messenger that connects nutritional conditions and weapons development in the body.

　This result is the first discovery of a case in which ILP specializes in the development of weapons, and suggests that ILP may bring about morphological diversity of insects.

Paper information:[PLOS Biology] A specific type of insulin-like peptide regulates the conditional growth of a beetle weapon