What attracts silkworms to mulberry leaves, their primary food source, is no longer a secret because Japanese scientists have found that a jasmine-scented chemical emitted in small quantities by the leaves triggers an olfactory receptor in the insects’ antennae.
Kazushige Touhara, from The University of Tokyo, says that the new finding contrasts the notion that insects are generally attracted to their host plants through the recognition of a blend of volatile compounds by a combination of receptors.
He says that the study’s results may have practical implications for those who raise silkworms for the production of silk.
"In the mid-20th century, several volatiles emitted by mulberry leaves were reported to attract silkworms. However, these previously identified odorants turned out to be weak attractants at best. None of the other abundant odorants in mulberry leaves attracted silkworms, either. Unexpectedly, we found that the potent attractant cis-jasmone was not an abundant volatile emitted from mulberry leaves at all; it is present only in small amounts," he said.
Indeed, Touhara and his colleagues have found that the threshold amount of cis-jasmone needed to attract silkworms appears to be significantly lower than the amount of any attractant to food reported for other insect larvae, such as fruit flies and mosquitoes.
During the study, the researchers narrowed down the compounds emitted by mulberry leaves to the one that attracts silkworms, and then went in search of the olfactory receptor genes responsible in the silkworms' genome. They ultimately found 20 olfactory receptors that were active in the antennae of silkworm larvae.
The researchers revealed that only one of those olfactory receptors was found to respond strongly to cis-jasmone.
They said that the insects would move toward the source of the smell whenever that olfactory receptor was activated.
Touhara said that cis-jasmone might be added to artificial diets fed to domesticated silkworms to increase the efficiency of their food intake.
He further said that the new finding could also have implications for pest control, as chemicals may be developed to block the underlying receptors in pest insects similarly attuned to single compounds so as to keep them at bay.
The study has been published in the online edition of the journal Current Biology.
