Bizarre male mosquitos with female traits may help stop dengue, Zika virus

Researchers at Virginia Tech have discovered a novel method for identifying genetic targets that could help control mosquito populations, potentially providing an alternative to insecticides.

The study investigated the genetic basis of species incompatibility by crossing Aedes aegypti , a primary vector for global arboviral diseases, with its sibling species, Aedes mascarensis , from the Indian Ocean. When the hybrid offspring were crossed back with one parent, about 10 percent of the progeny became intersex and were unable to reproduce.

These findings are crucial for controlling diseases such as Zika and dengue, as improved mosquito control can significantly reduce the transmission of these illnesses.

“This study can help identify new sex determination pathway genes that can be used in mosquito control strategies,” said Igor Sharakhov, one of the researchers on the project.

Creating an all-male mosquito population

The researchers identified abnormalities in the sex determination pathways of these intersex mosquitoes, discovering that while these mosquitoes are genetically male, they express both male and female genes, resulting in mixed physical traits.

By understanding these genetic factors, the researchers aim to develop strategies to create all-male mosquito populations, which could help control mosquito numbers by eliminating females. Additionally, this research could help identify genes that influence female mosquito behavior, potentially aiding future vector control methods.

Although insecticides have been somewhat effective in controlling mosquito populations, their effectiveness is waning, and they are not ecologically sustainable. This new genetic approach offers a promising alternative for mosquito population management and disease control .

“We studied the hybridization of two mosquito species, found that intersex individuals have disrupted sex determination pathways, and identified sex-specific gene expressions,” said Sharakhov.

Investigating mosquito larval stages

In their study, the researchers examined three key areas. First, they investigated the morphological and anatomical aspects of intersex mosquitoes, focusing on both external and internal organs, with particular attention to the reproductive organs.

Second, they explored the genes involved in the sex determination pathway. They specifically analyzed three genes: one master regulator to determine its expression levels, and two additional genes responsible for creating male-specific and female-specific splicing variants.

Lastly, they assessed the overall gene expression in these mosquitoes to identify normal and abnormal patterns related to sexual differentiation. This comprehensive approach aimed to unravel the genetic and anatomical factors contributing to the intersex condition and its implications for mosquito control.

“What we found is that the morphological abnormalities start in the pupal stage during development, and in adults, the most severe cases have both testes and ovaries in one individual, which is very unusual for these species,” Sharakhov said . “Now we want to understand what causes these abnormalities.”

Preventing Zika and dengue

The researchers discovered that intersex mosquitoes express both male and female variants of sex-determination genes, resulting in mixed physical traits. Although female-biased genes are expressed as expected, male-biased genes exhibit reduced expression in some male reproductive structures, while genes associated with the testes remain at normal levels.

This study has potential applications in mosquito control by identifying new genes in the sex determination pathway. Furthermore, pinpointing sex-specific genes could lead to the development of genetic constructs to manipulate traits in wild mosquito populations.

“Since the intersex is genetically male but expresses female transcripts, it provides a system to identify genes affecting female behavior, which can be useful for future vector control strategies,” said Jiangtao Liang, a postdoctoral associate in entomology.

For diseases like Zika and dengue , a deeper understanding of mosquito genetics can lead to more effective control methods, potentially reducing the global spread of these illnesses.

This study was published in the journal Communications Biology.