The illusions of destruction being not destruction were, patently, quite obvious, considering all upon Maltruse was alive and part of the Hive Mind. At first, the illusions worked, and the Psychic Scream did rebound; however, the Lorcar were much more attuned to their own powers and it hardly affected them. Once they noticed that their normal Psychic Power was being rebounded, they unraveled the illusions, beginning with Psionic methods of illusion then when that didn't work, by destroying the Magic from its framework up, making the Locusts unaffected by the illusions because the spells creating them simply were no longer there.
Of course, all this would be if not for the fact that the Anrufe members were inside of, and I quote, a 'anti-Magic bubble' which, by definition, would prevent their magic from working in the first place. Or even if it was simply Anti-Magic surrounding them but not actually touching them their spells still wouldn't go through it, of course. Their illusions and their destructive antics would be kept within their own bubble of Anti-Magic(which...Affects Psionics not, since the Lorcar are Psychic, not Magic in the slightest).
Even with the displacement field blocking all of the actual toxins from the air, the Anrufe would begin to feel...Sick. Unwell. With every breath they took, they were getting worse and worse. Soon enough, cysts were forming on their insides and pox spread across their bodies, and blood began to seep from pores along their skin. Tumors were forming as the virus took hold, and attacked their DNA. For you see...The Lorcar did not have only poisons in their atmosphere. They had their own bio-engineered virus, the Killer Cell Caste, everywhere, a virus created from the reverse-engineered DNA of the most dangerous pathogens even encountered by the Locusts in their history. And even as their own immune systems would try to counter it, they also had the Lorcar's Immune System, the Antivirus Caste of microbial cells, floating in them as well, which attacked and devoured white blood cell and non-Lorcar pathogen alike. If nothing was done, their bodies would be destroyed on a cellular level, reduced to diseased sacks of flesh and bone, no longer even recognizable.