Predation of T.marmoratus over L.boscai has been documented a few times and observed informally too. It seems that the incidence is relatively low, although if i recall properly, i think there was a study that showed that T.marmoratus females predate on adult L.boscai with certain frequency, at least in some populations.
Even if there is significant predation, i think L.boscai populations are capable of sustaining it, they have faster reproductive cycles and are quite numerous where the conditions are suitable. I doubt adults get eaten often, though, they are fast little buggers when they have to be.