They are ambrosia beetles and they will kill your citrus tree. They have also attacked my weakened citrus trees. spraying of the trunk and limbs will not kill the bugs, the chemicals cannot reach them, take a spray can of permethrin based spray and put a small straw on the nozzle, wear safety glasses and spray directly into each bored hole, after knocking the sawdust off. The beetles are only about a half inch into the hole. I use Bengal Roach Spray, 2% permethrin and it comes with the straw do this ASAP or you will lose the tree.