Can host plant specialization lead to speciation in herbivorous insects?

That's the main question to the research I am conducting now. I am interested in population genetics and evolutionary ecology, and the mechanisms of species divergence. I am studying the role and importance of host plant specialization as a barrier to gene flow in the juniper hairstreak butterfly, Mitoura gryneus. Mitoura use trees in the family Cupressaceae, including Juniperus ashei, J. virginiana, and J. pinchotii as host plants in different regions of Texas. I am comparing populations in terms of host plant preference and fitness on the preferred host, as well as genetic differentiation, for host-associated populations that occur together and in geographically separate areas. If specialization and assortative mating on the natal host plant is occurring, then patterns of neutral genetic variation should reflect this.
On a larger (temporal/geographic) scale, I would like to examine Mitoura throughout North America in terms of explaining biogeographic patterns. I want to examine specialization, host switches, adaptive radiation and speciation in some kind of a macroevolutionary framework, and I think giving attention to these little buggies might prove fruitful in this regard.