Can not answer your question except to point out a few things. Cornmeal is smaller sized pieces of cracked corn. Last time I checked a bug is a bug. What will kill one will kill another, good or bad, no difference.

Having had corn meal infested with bugs and living on a farm where we grew corn it is not very effective killing the bugs that eat on the corn plants. It may be effective on others.

I've been reading about corn in all fashions since the 90s and I've never seen anything reliable about it killing bugs...or anything else for that matter. Corn meal is food and it feeds things. If the corn meal itself doesn't feed something, then the fungi that decompose the corn feeds things. Some of those decomposition critters may kill grubs but I've never heard of that, either.

GMO's have not been proved to be toxic - at least not that I am aware of. The issue with GMOs is the unknown effects of changes in amino acids, as those amino acids get recombined into protein in other species that eat the corn. Although humans have been altering the genetics of plants for tens of thousands of years, nobody has complained until they started doing it artificially. It could be a problem but only time will tell.

I'm confused. By "altering the genetics" do you mean "controlling the breeding"? Viruses (and bacteria, if you count plasmid exchange) have been altering the genetics (literally) of plants since their dawn, but they weren't directed by humans until now.

In any case, you can read about GM corn here.

Altering the genetics by inserting differing dna into another groups dna to alter it. This is done on the microscopic level rather than breeding.

The herbicide resistance is generally refering to Roundup and it's sister products.

Corn like most plants have certain insectides and herbicides in the chemical structure of the plant. If they did not have these structures they would not be able to out compete the millions of other plants that want to grow in that spot and the millions of insects that want to eat the plant after it does start growing.

Some of the fungi that occur naturally on corn and other plants will kill many things but I have always doubted from what I have seen that corn seed or plant will kill the bugs that it is reputed to kill. Now gluten may be another story.