Help - Hibiscus disease or insect problem

I have a large (and previously healthy & hearty) hibiscus shrub. A few months ago, I noticed that it seemed to be thinning out - upon closer inspection, what appears to be happening is this - at the juncture of smaller twigs with the larger twigs, they are just breaking and falling down, thereafter the leaves turn yellow and the twig dies. It is happening even with some of the larger twigs at the juncture to even larger stems. There does not appear to be any critter type thing at this juncture boring the twig.

The hibiscus is valiantly trying to come back - all sorts of new little green leaves appear, but it doesn't seem to be able to keep ahead of whatever is doing this. Also, the nice green leaves appear to be spotted or stipled, even where the branches aren't dropping. They, too then turn yellow and drop off.

Today, I noticed a tiny red spider mite on one of the leaves - I know that they can cause the stipling and leaf spotting, but are they also the cause of the twig/branch problem? If so, what is the treatment of red spider mites.

Hope someone can help me - Thanks in advance.

June