pinus brepo

the only suggestion I can give is that we have had two bonsai pines for about 25 years grown from seed, in Japanese pots, and they need watering quite a bit in the Summer as they dry out quickly. Pines lose a few needles but if they lose a lot they are too dry. Larches lose their needles in the Winter. Sometimes there is a white furryness with the new buds. If they fall off it may be a fungal disease in which case spray them. Cut off the dead wood. Hope this helps. Lindak.

The White residue is likely to be some type of aphid which surrounds itself with the residue for protection, you will need to spray with an appropriate insecticide asap.
Just for information, your Pinus nigra 'Brepo' is not a miniature, it would be classed as dwarf, once established it will grow about 15cms per year and will be about 1metre wide x 75cms high in 10 years, Conifers classed as miniature should not grow more than about 5cms per year.