Existential Threats in America are clearly defined as things that threaten the comfort and well-being of the residents of Washington D.C. In Europe the range is limited to certain gated communities in Brussels I suppose, but here comes the possibility of one now.
With the influx of downtrodden refugees from the lower latitudes bearing only the credit cards and iPhones they could slip into their pockets, we are now discovering that they also bring a long list of diseases, many of which are transmitted by mosquitoes. Not so much a problem in winter, but in summer, the little bloodsuckers pop up even in the best neighborhoods. Additionally it seems things like Zika can be transmitted sexually adding a new element to the casual affair with the pool boy.
When Malaria, Zika, chikungunya and dengue fever, and who knows what all else begins to pop up in the tonier parts of town, then you'll begin to hear the cries to have another look at DDT. Back in '71 it was determined that it posed no real threat to anything with less than 6 legs, but got banned anyway mostly to win the green vote. Since then it's been banned pretty much worldwide with threats to places still afflicted with the aforementioned diseases and more to cut off trade if any traces are found in anything being shipped from those countries. The death toll from otherwise preventable diseases is estimated to be between 50 and 100 million since the ban went into effect putting Rachael Carson up there between Joe Stalin and Chairman Mao in terms of the absolute number of people they've killed.