Fighting the tiger mosquito: a bacterium reduces its reproductive capacity by 90 per cent

There is good news from Italian research into the insect that has dominated the summer: mosquitoes. For the first time in Europe, an innovative platform for the sustainable control of the tiger mosquito has been trialled on a large scale. This strategy is somewhat reminiscent of the Trojan horse trick and has also proved capable of naturally reducing the fertility of female mosquitoes, without harming the environment. The experimental campaign, conducted at the Enea Casaccia Research Centre (Rome) as part of a collaboration between Enea, Google LLC and Sapienza, involved 1.6 million ‘fake’ males, identical in appearance to those of the targeted species but rendered incompatible with females in the laboratory thanks to a bacterium. In practice, introducing these special males into the insect population reduces the ability to produce fertile eggs capable of surviving the winter by 88 per cent.

The tiger mosquito (Aedes albopictus), as well as being a nuisance during summer nights and days, can transmit various arboviral diseases, such as dengue, chikungunya and Zika, which are now also affecting Europe. The technique involves releasing large numbers of modified males which, thanks to a symbiotic relationship with a harmless bacterium – Wolbachia – are reproductively incompatible with wild females. The result? All the eggs laid by wild females are sterile, which has an impact on the mosquito population. ‘This approach, applied exclusively to the tiger mosquito, offers a viable alternative to the widespread use of chemical insecticides,’ explains Riccardo Moretti, a researcher at ENEA’s Agriculture 4.0 Laboratory.

The key to it all is the bacterium: it is present in most insect species with which it lives in symbiosis. Wolbachia makes the females in which it is present reproductively compatible. Females lacking Wolbachia, on the other hand, are rendered sterile by males harbouring this bacterium. Enea has replicated this natural mechanism by replacing the Wolbachia present in the tiger mosquito with another strain of the bacterium found in the common mosquito. By influencing the population dynamics of these insects over time, ‘the foundations are laid for a more lasting, effective and sustainable control of populations, keeping them consistently below epidemiological risk thresholds’, explains the scientist.

The ENEA research team was the first in the world to produce a line of tiger mosquitoes with the characteristics described. Google has developed this control strategy in parallel with ENEA to combat other mosquito species and is already playing a leading role in various large-scale implementation programmes in different parts of the world. In this project Google was tasked with increasing the population of the tiger mosquito strain that produces incompatible males – developed by Enea – selecting only the males, and organising their packaging and air transport from Miami (United States) to the release site in Casaccia.

For its part, Sapienza University of Rome, drawing on its expertise in the study of mosquitoes that transmit pathogens, is contributing to the programme by validating the technique and monitoring untreated control areas. Between late July and late October 2025, a total of around 1.6 million incompatible male tiger mosquitoes were released across the 53 hectares of the ENEA Casaccia Research Centre campus. The study is continuing this year as well. As Maurizio Calvitti, a researcher at Enea’s Sustainable Agri-Food Systems Division, explains, the Casaccia Centre ‘represents a pilot model of particular value for the transferability of the methodology to other operational contexts, both in Italia and internationally’. And it holds the promise of ridding us of these annoying and dangerous disease-carrying insects.