How does antibiotic resistance arise in bacteria? Or pesticide-resistance in insects too?

It's basically evolution. Let's say that you spray 1,000 bugs, for instance. 998 of them die, but for some strange reason, a quirk in their DNA, two of them survive. Those two are slightly resistant to the pesticides. They manage to reproduce, and a slightly higher percentage, let's say, 10 in 1,000, inherit the resistant genes. If you spray again, only these 10 will survive and reproduce. As the generations continue, more and more bugs with resistance appear. The more there are, the more selective it becomes, until only the most resistant bugs can reproduce and pass on their superior genes. After several generations, a pesticide-resistant group of insects has developed. The same process happens with bacteria.

How does antibiotic resistance arise in bacteria? Or pesticide-resistance in insects too?
The resistance arises the same way in both bacteria and insects. Whenever an antibiotic or pesticide is applied, it initially kills 99.9% of the organism. That seems like in would do the job, right?





But, it is the .1% that manage to survive that repopulate the environment with more resistant survivors. After a while the entire population is resistant and new antibiotics or pesticides have to be found.





It's an ongoing battle.
Reply:Selection. Natural selection if you'd like to call it that.


Neither artificial nor natural selection are perfect terms, but the mechanism is the same.
Reply:It's evolution , baby! These organisms are not identical clones of each other. Processes of mutation have created some variety in their genetic makeup, and sexual reproduction can add more variety yet.





When you spray (or dose) them, they naturally aren't all equally affected. Some will succumb very quickly, some will succumb slowly, and there may be some that won't even die from it. When these survivors breed, the next generation has a proportionally higher frequency of the genes that provided the mechanism for resistance, because the resistant ones of the first gen had a better chance of surviving to reproduce than the vulnerable ones.





When sprayed a second time, a greater fraction of the new generation would be expected to survive. And so on with further sprayings, until that chemical is no longer effective against them.
Reply:think of it on a larger scale. some people get the flu and some don't. something in their genetic code makes their immune system more affective against the flu virus.





same with bacteria. some bacteria is killed off by antibiotics, but not all. the ones that survive have something in their genetic code that makes it harder to kill. so we use a stronger antibiotic and most will be killed but not all.





basically we weed out the week bacteria, and the stronger leftovers come back with a vengeance, then we kill off most of those and the stronger left overs come back even stronger.





hope this helps!