Swiss scientists found that rootworms were attracted to soil containing predatory nematodes
Christelle Robert, University of Bern
These predatory worms have figured out meal delivery. Called entomopathogenic (for insect-killing) nematodes, they infect and feed on an insect, then multiply within its carcass. While feeding, the nematodes produce smells that attract their next insect feast, reports a study published October 13 at bioRxiv.org.
Farmers worldwide use this nematode to control insect pests, such as the western corn rootworm (Diabrotica virgifera). Because smells, or volatile chemicals, are known to drive many plant and animal interactions, scientists at the University of Bern, in Switzerland, examined whether the rootworm’s larvae, which eat maize roots, would avoid the smell of a nematode predator (Heterorhabditis bacteriophora). In the experiment, rootworms had to choose between two pots of maize plants. Surprisingly, up to two-thirds preferred maize roots containing nematode-infected rootworm carcasses over roots with uninfected carcasses or no carcass.
Scientists gave rootworms a choice between a maize plant in soil containing nematode-infected rootworm carcasses and a plant in soil with no infected carcasses. Most rootworms, lured by odors coming from infection, chose to move toward the more dangerous pot containing nematode predators.
When the scientists checked if infected carcasses emitted odors that attracted the rootworms, indeed, feasting nematodes were producing distinct volatile chemicals. Adding one of these chemicals, butylated hydroxytoluene (BHT), to an uninfected rootworm carcass made it an instant rootworm magnet.
Four of six other insect species (including a fly and a moth) also fell for the chemical lures, which were specific to each prey species. They gravitated toward nematode-infected carcasses of their own kind.
It’s still unclear why these chemicals draw prey insects to their doom. In the case of rootworms, says chemical ecologist and coauthor Christelle Robert, BHT may be a close mimic of smells the rootworms use to find plants to munch.
X. Zhang et al. Entomopathogenic nematodes increase predation success by inducing specific cadaver volatiles that attract healthy herbivores. bioRxiv: 10.1101/442483. Posted October 13, 2018.
S. Milius. Robins reject red glowing grub. Science News. Vol. 179, January 29, 2011, p. 14.