Best of two evils

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Best of two evils

Sometimes things happen whereby you ask yourself, is this smart. Like the spit of the tobacco hornworm, a butterfly, that transforms one of the fragrances of the tabaco plant. But this transformation causes the attraction of the tobacco hornworm natural enemies. Now Dutch researchers together with Belgian, German, and Taiwanese researchers have discovered that the enzyme that transforms the fragrance is also needed for a healthy development of the tobacco hornworm.

Plants distribute a fragrance bouquet during and after an herbivore attack. These can be repellents, toxic, attract predatory insects, or warn neighbouring plants. Plant eating insects, in their turn, influence plants during feeding with their spit, and the molecules therein. Often this spit causes a reduction in the amount of volatile compounds that the plant produce as a reaction to the feeding insect. But the spit of the caterpillar of the tobacco hornworm is doing something different. It is transforming the volatile Z-3-hexanal to Z-2-hexanal. A compound that is actually attracting the natural enemies of the tobacco hornworm.

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Without Hi-1 there is no healthy development

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To analyse why the caterpillar of the tobacco hornworm does this, the researchers first searched for the enzyme responsible. They separated the compounds present in the spit based on size. Following the researchers analysed which fraction turned Z-3-hexanal into Z-2-hexanal. From the fraction that was able to do the transformation they identified the proteins. This resulted in five proteins. But only one was actually turning Z-3-hexanal into Z-2-hexanal. This protein got the name Hi-1.

Subsequently the researchers studied the effect of the absence of Hi-1 on the tobacco hornworm. They noticed that it took longer for the butterfly to mature into an adult. Moreover, they saw that the butterflies had more deformations. This, so observed the researchers, was not a result of not being able to process Z-3-hexanol. Butterflies grown up on a diet without any Z-3-hexanol still took longer to develop and had more deformities.

What Hi-1 is doing during the development of the tobacco hornworm butterfly is still unclear, but that it is an essential enzyme is without doubt. Without it, there is no healthy development. Showing that sometimes you need to accept an unfavourable consequence because the alternative is worse.

Literature

Yu-Hsien Lin, Juliette J. M. Silven, Nicky Wybouw, Richard A. Fandino, Henk L. Dekker, Heiko Vogel, Yueh-Lung Wu, Chris de Koster, Ewald Große-Wilde, Michel A. Haring, Robert C. Schuurink & Silke Allmann (2023) A salivary GMC oxidoreductase of Manduca sexta re-arranges the green leaf volatile profile of its host plant. Nat Commun 14, 3666. https://doi.org/10.1038/s41467-023-39353-0

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