Why do some broad bean leaves have holes?

Holes in broad bean leaves are often the result ofthrip damage.

The thrips get right into the growing centre & the thrip larvae damage the minute, developing  leaves.  As these leaves grow, they are distorted & the damaged part of the leaf becomes a hole - which gets bigger as the leaf grows.

This gives the impression that something is eating the leaf now - but the hole was made when the thrip was damaging the growing centre where the leaf was forming.  Sometimes   the leaves around the growing centre have  black bits round the edges, almost  like they have been burnt.

Thripsnormallydamagemore than oneplant.

Blackflywillstart a colony on one broad bean plant, but blackflydo not make holes& they would be easy to see on the growing tip of the broad bean plant.

So, holes on broad bean leaves are usually due to thrips.