How is a mother fruit fly to protect her babies as they lie unhatched and vulnerable in your fruit bowl? The danger comes not just from other species of predators but also from hungry cannibal larvae, sometimes the babies’ own older siblings. In PLOS Biology (2019, DOI: 10.1371/journal.pbio.2006012), a team led by Roshan Vijendravarma at the Institut Curie in Paris reports that it’s uncovered the answer: Drosophila melanogaster use chemical deception to protect their eggs.
Back in 2013 at the University of Lausanne, Vijendravarma found that young Drosophila larvae hunt and eat older maggots, including those of their own flesh and blood. But even when they were starving, they never touched unhatched eggs. He wondered what made the eggs unappetizing.
“Initially we anticipated that we’d find some toxins,” Vijendravarma explains. But fruit flies don’t seem to pursue this strategy. That makes sense: you don’t want to poison some of your children just to protect the others from being eaten.
So Vijendravarma’s team started looking for alternative, nontoxic protective strategies. This led the researchers to the waxy coating of the Drosophila egg. The coating not only protects the growing larva from drying out but also contains the sex pheromone 7,11-heptacosadiene, or 7,11-HD. When Vijendravarma’s team removed the pheromone or damaged the waxy coating, the larvae ate the eggs.
Various species, including fruit flies, are known to use chemical communication, explains Matthew Cobb, who works on olfaction and pheromone processing in Drosophila larvae at the University of Manchester. In adults, 7,11-HD receptors on the legs of male flies help them identify females. Cobb says it is intriguing that the female sex pheromone also makes eggs unpalatable to maggots.
Vijendravarma says the general strategy of chemical camouflage could be useful. Perhaps we could protect food and crops by tricking pests with chemical signals derived from rival species, for example.
But regardless of applications, Cobb says this new research “gives us added insight into the unexpected complexity of chemical communication even in species that have been intensely studied.”