The case of the Apple maggot fly was brought up. Here here is a quote from the source cited. Note the it says "possibly". That means that it is not proven. I did not dig any deeper that is a far as I needed to go to show that it is not a proven fact. Quote from source. (Wikipedia) "Rhagoletis pomonella is significant evolutionarily in that the race of this species that feeds on apples spontaneously emerged from the hawthorn feeding race in the 1800 - 1850 CE time frame after apples were introduced into North America. The apple feeding race does not now normally feed on hawthorns and the hawthorn feeding race does not now normally feed on apples. This constitutes a possible example of an early step towards the emergence of a new species, a case of sympatric speciation. The emergence of the apple race of Rhagoletis pomonella also appears to have driven formation of new races among its parasites."