Both Swallows and Bats catch flying insects. I would suggest you have a mixture of nest boxes and try to attact birds that will eat green fly etc on the tree as well .
Here in europe I will be trying to attract Blue tits and great tits for that job.
Living in Anjou , France,
For the many not for the few
I think wild birds like an area which has lots of cover at different levels for them to dash into. An orchard with trees evenly spaced all the same height doesn't provide a lot of cover for birds, and they may feel too exposed to risk spending much time there. A nearby thorny hedge, or some stands of thick brush and undergrowth may be helpful in attracting birds, particularly if it includes some berry bushes or other edibles for them.
It may be that having stands of thick non-tree plantings (even just some thick stands of weeds) may distract the insects from your fruit too, and quite possibly attract beneficial predatory insects and smaller insect-eating vertebrates such as toads or snakes.
Do you have a water feature like small pond? Ponds are a great way to attract birds, bats, dragonflies, and predatory wasps. Many insect eating birds also eat seeds and berries. Planting millet, rye, elderberry, etc can help bring them in closer to find the real dessert.
Come join us at SowEdible.com as we build our 100 acre Permaculture homestead.
Don't count your weasels before they've popped. And now for a mulberry bush related tiny ad:
100th Issue of Permaculture Magazine - now FREE for a while