Reducing the population of the Asian tiger mosquito in Valencia by inoculating males with the Wolbachia bacteria investigated

Reducing the population of the Asian tiger mosquito in Valencia by inoculating males with the Wolbachia bacteria investigated

Asian tiger mosquito (Aedes albopictus), in the magnifying glass.
Asian tiger mosquito (Aedes albopictus), in the magnifying glass.

A team of researchers from the University of Valencia (UV) is working on two projects funded, one by the Valencia City Council and the other by the Ministry of Science and Innovation, to reduce the population of the Asian tiger mosquito in the city. Rosario Gil García, a professor at the institution in the Department of Genetics, directs the molecular research in both, which is being developed now, and whose objective is to introduce the Wolbachia bacteria into the eggs of mosquitoes and create a population that, when mating, gives rise to sterile embryos.

The rains of last week and temperatures above 22 degrees have caused the mosquito eggs, deposited in the ground, to hatch and, after four or five days, the number of these insects has increased. The Asian tiger mosquito (Aedes albopictus) can transmit diseases such as Zika or dengue - although less likely than the African one, Aedes aegypti - and with the trend towards an increasingly warmer environment, it is a vector of potential diseases to control.

Rosario Gil, researcher at the Institute of Integrative Systems Biology (I2SysBio), a joint centre of the UV and the Higher Council for Scientific Research (CSIC), explains that one of the biocontrol systems that is being developed against the tiger mosquito is the use of the Wolbachia bacteria, sometimes used to prevent viruses from being transmitted and other times to prevent mosquitoes from reproducing.

In Valencia, no recent cases of virus transmission of serious diseases have been detected with these mosquitoes, as has occurred in Catalonia, despite the fact that the Asian tiger has already been installed for more than 15 years, so attempts are being made. control its population, in a project in which the company Lokímica, specialized in pest control, also collaborates.

"Wolbachia is an insect endosymbiont, that is, bacteria that live inside insects in specialised cells. It is my line of work", explains the researcher. In the case of mosquitoes, Wolbachia, like most endosymbionts, is always located near the female’s ovaries to be transmitted from one generation to the next, directly through the eggs of the embryos. So what this bacterium does in the case of the tiger mosquito and the common mosquito, Culex pipiens, is infect the females for its own benefit.

"Cytoplasmic incompatibility means that if a male carries a Wolbachia and mates with a female that carries another type of Wolbachia, the embryo will be sterile and will not be born. The male transmits a toxin in his sperm and the female carries the antitoxin from her cytoplasm. If the antitoxin is not the corresponding one, it does not neutralise the toxin and kills the embryo, and this is what we are trying to achieve", Rosario Gil explains.

The Wolbachia carried by the common mosquito is incompatible with the Wolbachia that normally infects the tiger mosquito. "In our research, we want to find a native Wolbachia that is incompatible with the one carried naturally by tiger mosquitoes, produce large numbers of tiger mosquitoes infected with this new incompatible Wolbachia, and release males into the environment to mate with females", explains the researcher.

Furthermore, "currently, we are not only working with the Wolbachia of the common mosquito, we are also characterising the Wolbachia of Drosophila melanogaster, which is also incompatible with that of the tiger mosquito, to then choose one. At the Cavanilles Institute we are keeping the tiger mosquito cured of its natural Wolbachia and at the I2SysBio we are characterising the bacteria of the common mosquito and that of Drosophila. The next step would be to inject the one we select into the tiger mosquito before releasing it", completes Rosario Gil.

Rosario Gil’s current project, funded by the Ministry of Science and Innovation, until 2025, "Host-symbiont communication and its usefulness in the biological control of pests and pathogens, SYMB-CONTROL", has a section, "Molecular characterisation of native strains of Wolbachia in different insects, as a first step for its use in biocontrol", which is what is being applied with Aedes, Culex and Drosophila. The annual agreement with the city council is "Proposal for the generation of new strains of tiger mosquito and possible pilot test for the release of males (incompatible insect technique, IIT) for the control of populations in a delimited and controlled area of Valencia", and it is led by Antonio Marcilla, full professor of Parasitology at the UV.

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