All ILTs use energy to catch flies.
Reducing energy use will reduce your fly catch.

T12 lamps will outcatch T8 lamps.
T8 lamps may not save energy.

If the ballast in your trap doesn’t match the lamp,
changing to T8 lamps will not only reduce your fly catch,
it will produce less than expected energy savings, if any at all.
T8s may even use more energy than T12s unless the ballast is changed as well.