Like the other comments say, we *think* most bugs die to predation rather than old age, but we (zoologists/ entomologists) really have no idea.

Its incredibly difficult to tell because its basically impossible to track individual bugs in the wild. Most of what we know about the lifespan of animals in the wild comes from mark-recapture experiments, where a large number of animals are captured, marked with something like a leg band or other tag, and then some amount of time later another survey is conducted to see how many tagged animals are re-collected. This works really well for populations of vertebrates and gives us a pretty good estimation of how long animals live, based on the dates on the tags or other long term records. However, as far as I know, its virtually impossible to actually do this with insects (right now, at least). Dobzhansky tried a couple times with wild fruit fly populations but never got anything conclusive, and that's the most well known attempt I know of.

In regards to lifespan, it can be highly variable, and depends on how you define lifespan. Most insects typically live actively for a couple days to a couple years, but some insects can be alive for much longer. Insects can enter a state of hibernation called diapause where they remain in stasis for years at a time, like cicadas which famously hibernate for 17 years. Depending on how you define lifespan, there are insects that are technically alive for decades, but they spend the vast majority of it in diapause in their cocoons and are only active adults for a couple days/weeks/months at most.