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Male fruit flies reared in a lab are more successful at mating after an encounter with a robotic dummy designed to look like a rival male. The finding could boost efforts to control populations of the flies, which are a major crop pest.

The Mediterranean fruit fly (Ceratitis capitata) is one of the most destructive fruit pests in the world, found on every continent except Antarctica. There have been various attempts to rein it in by releasing large numbers of sterile males reared in labs. The aim is for these males to mate with wild females but produce no offspring, resulting in a population crash.

However, mass-rearing conditions in labs can reduce the flies鈥� ability to compete for mates with non-sterile males in the wild. Although sterilisation techniques are a factor in this, the same problems can affect non-sterilised insects reared for biological control programmes, such as the predators or parasites of pests.

at the Sant鈥橝nna School of Advanced Studies in Pisa, Italy, and his colleagues aimed to find out if the sexual success of mass-reared C. capitata males could be increased by provoking natural territorial behaviours using replica flies.

Male flies were introduced into an arena and allowed to establish territory on discs made from citrus leaves. Then, a 3D-printed, magnetic model fly was moved towards some of the flies鈥� discs using a robotic system underneath the arena.

The movement was designed to bring about an aggressive response. For example, the approached flies might strike the dummy rival with their wings or 鈥渂ox鈥� it using their forelegs.

Males that interacted with the fake fly were then used in a courtship and mating experiment. These flies performed significantly longer courtship behaviours and were more successful in mating with females than males that had no contact with the dummy fly.

Applying this approach could improve the success of sterile insect programmes by making the lab-reared males more competitive, says Romano.

But at the University of Veracruz in Mexico, who has carried out separate research exploring the mating success of sterilised insects, believes that it would be a challenge to scale up the use of robots for mass-reared insects.

鈥淚n practical terms, it is probably better to provide males with cages where natural interactions can take place. Providing more space and a semi-natural setting before release may give this same result as exposing males to robots,鈥� she says.

However, using robots and models to provoke natural behaviours rather than living animals would be more reliable, more repeatable and more ethical, says Romano.