Considering the consequences of losing so many beans, (here, it would be a serious look from Mrs Growster, which contains enough consequences to last until the winter), it's not rocket science to get to the root of the problem!
We grow about sixty beans in one row, so losing the potential crop from five plants means a loss of about 8%, which is not acceptable in my book, especially as a furtle for lurkers is a simple operation, and takes only a few minutes!
Why not organise a group Lurkerfest on allotments? Everyone appears, with a plastic sheet to lie on, or maybe even a camp bed, and is supplied with a Lurkerlamp, specially designed for the process! (These are available for £350.00 + vat from Growsterlurks Inc), and there is a prize for the number of lurkers discovered. Lurkerlamps will also work up to an hour after darkness, so that means they can be used for nearly twenty hours a day; more than enough to hoik out lurkers after the initial furtle!
I don't really know why I give all this advice for free - there's many a gardener who would pay a lot of cash for such information, but being an amiable old chap, I'll not charge a single penny...