I don’t follow the logic of this article. The plants have a gene which produces a toxin that kills whiteflies. If the whiteflies acquired this gene they would make a toxin that kills whiteflies and the larva would die before the fly even matured.
What the whiteflies acquired was something (either a gene or epigenetic change that persisted in offspring) that blocked the action of the plant toxin from disrupting the whiteflies metabolism and killing it. This happens all the time in nature and is called descent with modification (mutations). Any whiteflies with this mutation would thrive and displace any whiteflies that were still killed by the plant toxin. Either I missed something or this article is woefully confused in its explanation.
Finally found something coherent! The gene doesn't produce the toxin, but protects the plants from their toxins, and so also protects this particular species of whitefly.
This gene may have an important function in plants. The plants generate toxins to defend themselves from attack by animals. The team suspects that the BtPMaT1 gene may help plants store these toxins in a harmless form so the plants don’t poison themselves.