Sterile tiger mosquitoes released
In southern Germany, sterile tiger mosquitoes were released whose genetic material was radioactively irradiated. These tiger mosquitoes are infertile and should help to eradicate infectious diseases.
Per se, they are sterile tiger mosquitoes. According to "Technology Review," several cages, each containing a thousand irradiated males, were opened near Heidelberg at the end of July 2017. Should they mate with free-living tiger mosquitoes, the offspring will die.
"The tiger mosquito transmits many dangerous diseases such as dengue fever," says campaign manager Becker. "That's why we want to get rid of them." Tiger mosquitoes are considered very aggressive, and the black-and-white or red-and-white striped mosquitoes bite even during the day.
Since they can transmit against 20 tropical viruses known so far, German authorities are trying to prevent their permanent settlement in Germany.
Infection low
Tiger mosquitoes have been registered in southern Germany for a good 10 years. The tiger mosquitoes are not native to this country and occur only sporadically. Freight trains and trucks bring them in from southern Europe, especially along the A5 highway. So far, Becker's team has detected them in Freiburg, Heidelberg and Sinzheim.
To become dangerous for humans, however, the mosquito must first become a virus carrier itself - for example, by biting an infected returning tropical traveler. In Montpellier and in Italy, there has already been one outbreak caused by tiger mosquitoes.
The sterile insect technique based on radioactive radiation has been around for fifty years. With such sterile tsetse flies, the island of Zanzibar got rid of the dangerous sleeping sickness. But the radioactive radiation damages the genetic material of the insects indiscriminately and massively. That is why they are less fit than their wild counterparts.
The method therefore failed in the case of the malaria mosquito. The females were simply too reluctant to mate with the unfit males from the laboratory. Becker's team in southern Germany must now compensate for the lack of fitness of the radioactively irradiated males with sheer mass. For every male tiger mosquito living in the wild, he produces ten sterile males, three thousand per hectare.
Just because there are only a few hundred of the pests in Heidelberg, the plan of local eradication could work.
Irradiated mosquitoes
His team currently releases 15,000 to 20,000 manipulated males every week. Mosquito specialist Romeo Bellini from the Centro Agricoltura Ambiente Giorgio Nicoli in Bologna has damaged their genetic material so massively with radioactive gamma radiation that the males cannot produce viable offspring.
However, the effect of the intervention is still uncertain. Last summer, 15 percent fewer tiger mosquitoes hatched after the sterile males were released, one student counted. That's not enough for eradication. Because the males are smaller than the females, the two sexes can be separated by simply screening out the pupated brood.
Results from this year on the consequences of sterile tiger mosquitoes released are not yet available.
The Wolbachia Method
Verily takes a different approach. The Alphabet subsidiary uses the bacterium Wolbachia, which occurs naturally in 60 percent of all insect species but not in Aedes aegypti, to sterilize them. Males infected in the lab are "not limited in fitness as they are after radioactive irradiation," explains Verily researcher Jacob Crawford. The company has already begun releasing 20 million sterile mosquitoes of the Aedes aegypti species in California, which spread yellow and dengue fever, as well as Zika virus. The results of the campaign are still pending.
What both approaches have in common is that they do not involve genetic engineering - in stark contrast to several projects in Brazil. (Source: Technology Review)
