Isomerizing Saliva Guides Moth Egg-Laying

When a hawk moth caterpillar (Manduca sexta) munches on certain plant leaves, enzymes in the caterpillar’s saliva isomerize the double bond of the leaf chemical (Z)-3-hexenyl acetate to (E)-2-hexenyl acetate. Catalyzing this seemingly benign conversion is a critical problem for the caterpillar. That’s because (E)-2-hexenyl acetate attracts predators from the Geocoris insect family of big-eyed bugs, which then dine on the caterpillars and unhatched eggs, previous studies show. But adult female hawk moths also sniff out the (E)-2-hexenyl acetate produced by the caterpillar saliva enzymes, reports a research team led by Ian T. Baldwin and Bill S. Hansson of the Max Planck Institute for Chemical Ecology, in Germany (eLife 2013, DOI: 10.7554/elife.00421). The team notes that the odor alerts hawk moth females to avoid laying new eggs on caterpillar-chewed leaves that emit the volatile odor. This response lowers competition among hatched larvae for food resources and also reduces the risk of newly laid eggs being eaten by predators, the researchers note.