Question
Clusters of leaves are falling off of my Pin Oaks. Also the bees are so thick that you can hear them swarmming. The trees are 50 feet tall and about 24 inches in diameter. We live near Kansas City, Missouri. If I treat the trees with a ground application insecticide what ones would you recommend? Would you recommend the same for white pine trees?

Answer
The small twigs sounds like damage from an insect called a twig girdler or twig Pruner. These beetles cause very conspicuous damage in late summer. The leaves on large numbers of twigs and branches will be observed to turn brown prematurely. These twigs and branches sometimes fall from trees in great numbers and accumulate. On close examination, the twigs have one of two kinds of damage. Twigs damaged by the twig girdler are cut as neatly as by a knife. The cut end has been gnawed almost straight across with a faint rounding and is slightly roughened by the chewing. The twig girdler is more commonly found on pecan and hickory. The twig pruner causes a slightly different type of cut. The twig will be observed to have a hollowed out space at the cut end filled with sawdust like frass. The twig when split open will have a long tunnel through most of its length. The twig pruner is more commonly found on oak.
These insect lay their eggs in the twig and then cut the twig so it falls to the ground where the humidity is higher and the eggs can hatch faster. They really do not cause any health problems to the tree except for the few twigs cut off. To cut down the population next year the treatment is to just pick up the twigs and destroy them.
Since the twig cutter larva is in the twig when it falls from the tree, gathering and burning of the girdled twigs is the most satisfactory means of preventing further damage. This control works provided it is thoroughly done and extended some distance in the surrounding area. This form of control, however, is of limited value if the trees are growing adjacent to wood lots, where these girdlers are abundant, but should still be practiced. Spraying has not shown much promise for control of these species.

The soil applied insecticide are for sucking type insect and IF the tree is dripping sap the bees are gathering the honeydew that is secreted by the sucking insects. In this case I would use Bayer Tree and Shrub Insect Control. Here is a web link to this product. Check with your local nursery for the Bayer product. Yes it will work on White pine also.
http://www.bayeradvanced.com/product/Tree-Shrub-Insect-Control/concentrate.html