Study finds exploiting ‘fruitless’ gene could stop mating mosquitoes

By Stephen Beech

Disease-spreading mosquitoes could be decimated by preventing them from seeking out mates, suggests new research.

Previous studies have shown that male mosquitoes are attracted to the sound of female wingbeats.

Now scientists have discovered that a “fruitless” gene in the species is responsible for the male’s ability to locate and mate with females by listening for their wingbeat sound.

The researchers found that mutating the gene in males of the yellow fever mosquito makes them incapable of locating females to mate with.

Scientists have long studied the reproductive mechanisms of mosquitoes to control their population sizes and prevent them spreading dangerous diseases — such as yellow fever, malaria, dengue, Zika and several forms of encephalitis.

Now researchers at Nagoya University in Japan, working with Daniel Eberl from the University of Iowa in the U.S., have made a new breakthrough.

Eberl says the yellow fever mosquito, Aedes aegypti, is a “vector” of diseases including dengue fever and Zika fever as well as yellow fever.

He said: “At dusk, males gather to form swarms, where they detect the wingbeat sounds of females flying into the swarm, pursue them, and mate with them.

“After mating, females search for a host, take blood, and lay eggs.

“Hearing is an essential sensory modality for males to mate and elucidating the mechanisms underlying hearing is expected to lead to new strategies for controlling mosquito reproduction.”

Eberl explained that, in insects, one of the genes that generates sex differences in neural function is fruitless.

Previous studies using fruit flies have revealed that fruitless is primarily responsible for generating sex differences in behavior.

In the new study, published in the journal PLOS Biology, the research team worked out the influence of fruitless on the behavior of male mosquitoes and their hearing systems.

Eberl said: “A mosquito’s ‘ears’ are auditory organs that detect sound.

“The ear consists of the Johnston’s organ located at the base of the antenna and the long flagellum extending from it.

“Mosquito ears are highly sexually dimorphic, and there are substantial differences in the frequencies of sound to which male and female ears are tuned to.”

In the study, the research team discovered that fruitless mutant males, unlike normal males, do not gather with other males at dusk and instead exhibit female-like behavior.

While normal males displayed strong attraction to frequencies matching female wingbeat sounds, mutant males were not attracted to any of the frequencies tested.

In the ear, the research team confirmed strong expression of fruitless in the Johnston’s organ, suggesting the gene is involved in ear function.

Eberl said: “Upon further examination of ear performance, mutant males featured several distinctions from normal males.

“Normal males vibrate their ears for peak sensitivity towards female wingbeat sounds.

“However, mutant male peak sensitivity was shifted higher, outside the frequency range of female wingbeat sounds.

“Furthermore, sound detection of mutant males was severely impaired, with auditory neuron response to sounds being one-sixth of that in normal males.”

He says only mosquito ears, across all insects, contain auditory efferent neurons, which project from the central nervous system to the ear and modulate hearing function.

Eberl said: “Interestingly, close examination of the internal anatomy of Johnston’s organ revealed that mutant males had an altered auditory efferent network compared to control males.

“Mutating the fruitless gene partially feminizes males and impairs them from being able to amplify sounds.”

The researchers say the fruitless gene is assumed to directly suppress female-type genes while indirectly enhancing male gene expression.

By analyzing RNA sequencing datasets from mosquito ears, the team identified changes in the expression of genes that encode dyneins, large molecular motor proteins previously linked to differences in hearing function between the sexes.

Eberl said: “The types of dynein highly expressed differred between mutant and wild-type males, which may contribute to hearing amplification function impairment in mutant males.

“The accumulation effect of changes in expression of multiple dyneins is assumed to establish the male-specific ear that enables males to detect female wingbeat sounds.”

He added: “This research revealed that fruitless is responsible for establishing male auditory function and the findings may have applications for mosquito control.

“Because males must hear female wingbeat sounds for mating to occur, targeting fruitless and its downstream genes may make it possible to interfere with the earliest stages of reproduction.”