Hi Judith,

Sorry for the delay!

From what I can see in the photo, it looks like your pine has Woolly Pine Adelgids, a type of woolly aphid in the genus Pineus.  They are densely covered with wax, which is what makes them look like cotton lint stuck in the tree.

Under most circumstances, these insects cause little lasting plant injury though they are conspicuous.  Very heavily attacked trees can have needles that yellow, or their growth may be stunted.  

The first treatment option to try is to blast them off with a very strong jet of water.  They are attacked by some natural enemies, so insecticide treatments can backfire, as they can kill more of the natural controls than the aphids.

Horticultural oils applied in the dormant season (next winter) can also help to limit the size of infestations; the oils smother the aphids.  Oils applied now, though, can also damage the tree because of the weather conditions.  

Insecticidal soaps can be effective against aphids, but do be sure to read the label and apply according to instructions.  When the weather is hot and dry, insecticidal soaps can also damage plants.  

Other insecticides, including imidacloprid, can be effective too if these other measures fail; be sure to read and strictly follow all label instructions for any pesticide.

I hope this is helpful!

Cordially,

John