Thanks all.  I'm starting to get the picture.  It is much as I had thought, but it pays to be sure.  Seems no one knows for sure, since even out here where summers are short and winters brutal, that the authorities are worried.

I did a brief web search for something in the way of detailed information about the life cycle and their temperature tolerance, but web searches are not what they used to be.  They seem to turn up less and less real information.  Maybe I need to try a different search.  I have little time for that right now.  If anyone has good bookmarks, URLs of detailed info would be appreciated.

What I have found so far is minimal.  Several sites say the following:

"The beetles' life cycle starts with eggs, which are laid in the hive and hatch into larvae within 2 to 3 days. Ten to 16 days later, the larvae crawl from the hive and drop to the ground outside, where they burrow into the soil and pupate. In about 3 to 4 weeks, they emerge as adult beetles and re-enter the hive a week later. This process may repeat itself several times a year, especially during the warmer months".

So far, what seems apparent is that it takes about 45 days for an egg to become a mature adult so that the cycle can repeat.  That requires a ground temperature greater than (what?) for the pupation to be successful, and that is after almost about two weeks as a larva.  I don't know how many eggs an adult female lays at once and how long she will continue laying or if she lays a few batches and that is it. Anyhow, if the conditions are not just right, there is no multiplication and the problem remains minimal.

If, however, the temperatures are high enough and the soil is of the right type, the numbers can increase very dramatically every 45 days until the conditions become unfavourable.

So, it seems that what will determine whether SHB become a problem in a region will be

* The number in the initial infestation (or spring)
* The soil type
* The length of time in the summer that the soil is warm enough for reproduction.

Like varroa, it seems to be a question of how much SHB can multiply in the time that they have.  For varroa, it is the time from sealing of the cell to emergence of the bee.  With SHB, it is the time from soil warming to reproduction temperature until the soil cools below reproduction temperature.

Additionally, it seems that if the soil reaches a cold enough state over winter, that there is no survival to provide an initial infestation the next spring.

Do I have this right?

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