I cannot speak to whether bees are bothered by them or not, but it should
be understood that the voltage (electrical pressure) of power lines has
little to do with the magnetic field generated thereby.  It is the current
(flow) that induces the magnetic field.  Since the group of wires form a
circuit with current flowing in both directions, the magnetic field at any
reasonable distance cancels out.  Being closer to one wire than the other
might result in a small net field.   Directly below the center of the group
of wires there will be little net field.  Since larger spacings tend to be
used with higher voltages, the fields will tend to take a larger distance
to be cancelled on such lines.  There is also an electrostatic field that
IS proportional to voltage.  It also tends to be cancelled out amongst the
wires of the circuit.

Bee keeper
(and presenter of seminars on transmission lines)