You're right Sue.
I should have said that throughout history, there has been a guy whining to his wife, "Honey can't you do something about these bugs? By the way, where are my socks?"
How true. :v:
I also think it is due to the increased mobility of people. Tropical bugs (both the crawly kind and the microbial kind) are making their way across borders. And no, before LIP gets all YouTube about it, it's not just south of the border. People in general are traveling a lot. I've been sent to Europe for a two hour meeting, that's becoming more and more common. The world is simply getting smaller. Trade has increased worldwide, too. Plus, there are simply more of us. The population has gone from 200 million to 300 million in the US since the 70s. More people = more hosts, both humans and animals. There are animals that flourish in our presence like mice, opossums, raccoons, squirrels and deer. All of those are yummy treats for a multi-host tick.
Pesticide resistance is probably playing a role in this, too. Organochlorines like DDT, pyrethroids like permethrin, and organophosphates like chlorpyrifos or diazinon have been used extensively. Some tick populations are just not sensitive to these anymore. As the climate gets warmer and more life stages of ticks survive cold seasons and don't go through a diapause, they are more successful. Pair that with being exposed to pesticides, and resistance happens. It's scary to imagine, but the estimate for the lifespan of a chemical before we start to see real resistance to it is about 10 years. That window will probably get smaller as the climate warms.
I just got back from south Texas where I was looking at horn fly populations. We have plenty of them in NJ, they are little bloodfeeding flies that plague cattle and deer. They do not have a diapause down there and are active all year, so controlling them is next to impossible. At least the cattle get a break here, at least for now.
The incidence of diseases has increased and changed geographically as a result of all of this, too.
That is my fifty cents on the subject.