Hi,
That's a great project with an interesting question. The only problem with your experiment is that E coli bacteria are specific for mammals and won't infect a worm. Also, the immune system of an insect is very different from that of humans and other higher animals.
Why did you choose mealworms as your test subject? Acai berries and blue berries both contain antioxidants and other substances that may have health benefits, but measuring their effects on the immune system using an insect may not be possible without access to an advanced research lab.
I am assuming that you are interested in seeing if antioxidant foods can make the mealworms' immune system stronger. I did a search for this and found several hits, all rather technical and not especially useful. Here's an example:
https://www.google.com/url?sa=t&rct=j&q ... aQ&cad=rja
One thing I did learn was that the mealworms which are the larvae of the Tenebrio beetle can be infected by soil fungi and bacteria. I'm not sure how you would do this but you could set up three batches of mealworms in dirt (use soil from the woods not packaged garden soil which may be sterile). One group would be fed with acai berries, one with blueberries and the last with something neutral like lettuce, or maybe nothing at all.
My assumption is that woods soil contains a mix of bacteria and fungi, one of which
may infect mealworms. If you were working in a research lab you would add a small amount of a specific fungus or bacterium to the soil but I don't know where you could get a culture of such an organism.
What you will be looking for in this experiment is how well the mealworms survive and how many pupae and beetles they produce. You will have to count the number of mealworms that you add so each bin gets the same number.
I have no idea if this will work. Maybe one of the other experts can come up with another way to measure immune response using insects.
Good luck!
Sybee