Killing Roaches Softly
I hate roaches more than I hate anything on the planet. Their mere presence stimulates revulsion in me, and I love nothing more than watching them suffer. These are strange emotions I would never consider releasing even on other insects of the same size or complexity; I even feel bad stomping on beetles who just *look* like roaches.
So how about someone out there run this experiment: design me some cannibalistic roaches.
You'd need a deserted island (near New York City for the climate most similar to where you'd launch the results, and so that I could burn it to the ground once the experiment was completed.)
Isolate pairs of same-gender cockroaches, because otherwise they'd play "last roaches on earth". Keep them without food for days or weeks on end. Watch for pairs where one would eat its cellmate to avoid death. (No use in breeding pairs where one waited for the other to die before feasting on it.) Take these slightly-cannibalistic survivors, breed them, and repeat results on the new crop of young. Watch for suspiciously obese teenage cockroaches. Reward them for their horrific gluttony with sweet, sweet breeding. Rinse and repeat.
Branch out, and watch for subjects who would prefer to eat their compatriots even in the presence of cardboard (known to be cockroach food during lean times) or in the presence of living plant matter (is salad nutritious to Mr. Roachy?) Perhaps you could discover subjects who would prefer other roaches to standard human leftovers - dirty dishes, Twinkie wrappers.
It's possible this would never happen, but god it'd be worth it to try. Yes, you'd be breeding carnivores. No, you'd have to weed out the carnivore instinct by isolating ones who specifically went for fellow roach flesh. I don't care for rats either, but I sure as hell don't want to see a roach who would consider taking one down.
Alas, I would be unable to partake in this experiment since even writing about it is kinda creeping me out. Plus, I'd vomit all over the test subject holding areas - which would torture the roaches by dangling bile-sweet food particles right over their cages. Too cruel. This isn't Guantanamo.