Are these species reprodultively isolated or not?

You can also use different methods of molecular taxonomy and phylogeny (i.e. rDNA analysis (maybe also with secondary structure of some parts), plastid DNA analysis, microsatellites analysis, SNP finding, AFLP, RFLP, DNA fingerprinting and other techniques) are good for species delinaetion, notably in combination with other techniques.

Following Andrii.... hybridization experiments can demonstrate whether they are isolated  or not.....easy confirmation of species status.....also cytological experiments may show chromosomal similarity or differences in addition to DNA evidences. Often morphological differences reflects chromosomal doubling or changes.

There are two things you need to demonstrate convincingly:

1. The two forms are species. This is relatively easy, and is best demonstrated if multiple lines of evidence demonstrate the same two groups (diagnosable morphology, diagnosable cytology, reciprocal monophyly of DNA sequences, microsatellite analysis showing two clusters). This would document lineage divergence (phylogenetic independence).

2. Speciation took place in the face of gene flow. This is much more difficult because it is nearly always possible to think of a scenario of allopatric divergence (Futuyma, DJ & Mayer, GC 1980. Non-allopatric speciation in animals. Syst. Zool. 29: 254-271). This is why the most convincing cases so far have been on oceanic islands or in crater lakes. In any case, you must demonstrate that the two species are each other's closest relatives, and preferably also that their distributions show a large degree of overlap (making allopatric divergence less likely), that the two species are young (the older, the more difficult to rule out allopatric divergence), that there are ecological differences between the two species (more of less necessary for sympatric speciation to start), and that their genomes are divergent at loci that are associated with ecological differences (indicative of ecological speciation), but not divergent at neutral loci (i.e. homogenized by gene flow). This can be investigated with RAD-seq technology. See Feder, JL., Flaxman, SM, Egan, SP, Comeault, AA & Nosil, P 2013. Geographic mode of speciation and genomic divergence. Annual Review of Ecology, Evolution, and Systematics 44: 73-97.