Topic: How long will a hive last untreated for varroa
One year, two years, or even three years?
Well, although with so many variables involved that question is impossible to answer with any certainty, nevertheless I think it's a good question to have asked - with the reality in practice for many beekeepers (but not all) tending to be between 2 and 3 years. That assumes by 'untreated' one includes all forms of physical treatment, such as artificial brood breaks, removal and destruction of drones within drone-comb and so on ... as well as chemical treatments.
Year 1 is invariably trouble-free, as colony collapse from a Varroa infestation is essentially 'a numbers game' based upon the initial numbers of mites which then 'seed' a colony's future Varroa population. Thus, in year 1 there will probably have been some significant disturbance which becomes reflected in the reduced number of mites initially present within a new colony - such as swarming, chemical or other treatment by a previous beekeeper, and so on ...
The 'best case' scenario is where a colony starts off the first season with Zero mites present, but then picks up a few - perhaps sometime towards the end of year 1. Those few mites will duly overwinter to have a much 'earlier start' within year 2. During year 2 that tiny mite population will follow behind the brood population numbers, increasing perhaps to several hundred (the actual number being anybody's guess). There will undoubtedly be losses due to grooming, mites simply falling-off bees, and mites being spread to other colonies - with the remaining number of mites being insufficient to cause the colony's demise as it overwinters after year 2.
But year 3 may then start with a mite population of a hundred or more, which will be quite sufficient to build-up - again with mite numbers always following behind brood numbers - to a very serious infestation level towards the end of year 3.
In the autumn (fall) of year 3 a cursory inspection will undoubtedly reveal a very powerful colony about to enter the winter period, only for a total colony collapse to then occur - the reason being that as the honeybee brood numbers declined in autumn, the number of mites had by that time peaked, with the colony's fate then being sealed, with the 'collapse' itself occurring slowly but inevitably during the winter period when the hive is closed-up and with those events thus being invisible to the beekeeper. Then - come the spring of year 4 - the hive is opened, and - with great surprise and disbelief - discovered to be completely dead.
The 'worst case' scenario has a similar pattern, except that in year 1 the colony acquires a similar number of mites as seen at the start of year 2 of the above - and thus the timetable is advanced by one year - otherwise the story is identical.
LJ