Why sex makes female ticks fat

Research published online this week in PNAS suggests that a peptide cocktail transferred from male ticks to females during copulation not only stimulates the females to gorge on food, but also stimulates the development of the ovary and the degeneration of salivary glands, preparing females for the reproductive tasks ahead.

Previous work has shown that virgin female Amblyomma hebraeum (African cattle ticks) will not feed beyond a “critical weight” of around 10 times their unfed body mass, but mated ticks will. W. Reuben Kaufman, professor of biological sciences at the University of Alberta, and his colleague Brian Weiss identified this “engorgement factor”—which they have termed “voraxin”—and show it to be a combination of two peptides that are upregulated in the testis and vas deferens of fed, but not unfed, males.

“If an effective vaccine can be derived from voraxin, the anticipated results from reduced feeding would include...