Fruit flies use sex chemicals to hide eggs

Fruit flies – and quite possibly other insect species – coat their eggs in sex pheromones to disguise them from hatched larvae hungry for a feed, research shows.

The discovery, by scientists led by Sunitha Narasimha of the University of Lausanne in Switzerland, illustrates a novel solution to a common problem among species that lay eggs but do not provide parental protection.

Many species reduce the chances that their eggs will be eaten by laying them in communal collections. It’s a good tactic for lowering the odds of predation by other species, but little use against cannibalistic members of their own. Indeed, it rather encourages the practice.

The result is a classic evolutionary balancing act. Cannibalistic larvae increase their own chances of survival by reducing competition and securing food. And that’s good. However, the same process also reduces the total number of individuals that hatch and go on to breed, thus restricting diversity. And that’s bad.{%recommended 8313%}

As a result, species faced with this dilemma have evolved a range of ant-cannibalistic adaptations – but here, too, there are issues and strict limitations on effectiveness.

Writing in the journal PLOS Biology, Narasimha and colleagues note that such strategies have to be non-toxic in nature. Making eggs poisonous, after all, would result in the death of cannibalistic larvae and the egg itself, to the marked detriment of the evolutionary fitness of the species.

The researchers reveal that the fruit fly (Drosophila melanogaster) has evolved a particularly cunning solution to the problem.

Using high-resolution mass spectrometry, the scientists discovered that fruit fly egg shells contain a very thin layer of wax made up of molecules from sex pheromones secreted by both parents. 

Among these was a female pheromone called 7,11-heptacosadiene, or 7,11-HD. In adults, the molecule stimulates mating – but, it turns out, it also functions to mask the presence of an egg from any nearby hungry larval siblings.

Narasimha and colleagues discovered that the protective power of the pheromone was so strong that it could even mask the smell of yeast – a substance normally irresistible to young fruit flies. It also served a secondary, protective function, effectively sealing the egg and preventing it from drying out.