Science fiction isn’t so far out with its idea of a virus giving vampires and zombies a craving for blood and dead meat. The concept of a virus modifying the eating habits of its carrier does exist in nature. Without the gory details though. That’s probably why Hollywood hasn’t picked up on it. An insect’s appetite for plants modified by a virus doesn’t make a great horror story. But, hey, life is not a movie. In the real world it’s not about zombies and vampires but about the aphid Rhopalosiphum padi.
Aphids feed on plant sap. Farmers and gardeners don’t really like them because they cause damages to their cultures and flowerbeds and they are vectors for several plant diseases. When eating from a diseased plant, the insect also ingests viruses that it transmits to the next plant it feeds on.
As for all living organisms, a virus characteristics are shaped by natural selection. Any new characteristic that allows the virus to be transmitted more effectively will become more frequent in the virus population as the viruses with this characteristic are more successful at reproducing and will be more numerous. Consequently, viruses should have evolved mechanisms to increase their transmission. Researchers had already observed that volatiles emitted by plants infected with the Barley yellow dwarf virus attracted Rhopalosiphum padi aphids and they wondered if the virus could directly influence the insect’s behavior in order to increase its transmission.
They fed aphids with an artificial sap that either contained Barley yellow dwarf virus particles or no virus and then presented the insects with the choice to feed from an infected or a non infected wheat plant. Aphids with the virus and those without it showed different preferences. Aphids carrying the virus chose the non infected plant while aphids free from the virus were more inclined to feed from the infected plant. It’s a win-win for the virus: the preference of virus-free aphids for infected plants promotes its acquisition and the change in aphid eating habits it triggers promotes its transmission, which ultimately boosts its spread.
Just like it does for zombies and vampires. Well, at least for the last part. Non infected humans tend to run away from zombies and vampires.
Ingwell LL, Eigenbrode SD & Bosque-Pérez NA (2012). Plant viruses alter insect behavior to enhance their spread. Scientific Reports, 2 DOI: 10.1038/srep00578