Photo/IllutrationMulberry leaf latex can cause digestive failure in spodoptera litura. (Provided by the National Agriculture and Food Research Organization)

In a possible breakthrough in pest control, Japanese scientists have uncovered the mechanism of how a unique protein in mulberry leaves kills most bugs--but not the silkworm.

The protein is also harmless to humans, according to the study team led by Kotaro Konno, a senior researcher at the National Agriculture and Food Research Organization (NARO) in Tsukuba, Ibaraki Prefecture.

“In the future, the protein may be artificially compounded to spray (on crops), or vegetables could be genetically modified to produce this protein themselves to ward off insects,” Konno said.

Over millennia, humans have enjoyed the mysterious fiber produced by the soft, white silkworms.

But only in recent years have Japanese scientists discovered that mulberry leaves, the only food source for silkworms, is poisonous to all other insects.

In earlier studies, mulberry latex--the white liquid secreted from the leaves--was fed to the larvae of other moths, including spodoptera litura and mamestra brassicae, a known garden pest.

These larvae stopped growing with even a tiny amount of the latex ingested, and they died within few days.

The latex had no ill-effects on silk moth larvae.

A further analysis of the latex led to the discovery of a protein named MLX56.

The latest study showed the protein bonds to and thickens the peritrophic membrane that most insects have inside their digestive organs. The digestive system eventually fails, and the insects die.

So far, MLX56 has been found only in mulberry leaves.

The compound’s effectiveness to ward off pests may not be as instantaneous as chemical pesticides. But since it is derived from a plant, it is more environmental friendly.

Humans do not have a peritrophic membrane, so the protein does not affect them.