I don't have a direct answer to your question, just a bit of information which may be useful:

"Planting is recommended in a firm seed bed at the minimum depth which will secure good coverage and sufficient moisture to promote quick germination and growth. Plantings at less than one inch may lack moisture, while deep planting may hinder or prohibit the seedlings from breaking through the surface and may add to the possibility of damage by the bean maggot."

I was unaware of the bean maggot, so I did a quick Google search. The only other info I found related to use of insecticides, including one university site which said, in an article dated 1982, that insecticides are the only remedy for a bean maggot problem.

Jim

Here is a link that might be useful: Seed Planting and the Bean Maggot

I just had the same thing happen to me! These maggots totally destroyed my bean seeds before they could germinate. I have now gone through two rounds of bean seeds and the maggots got them both times. This time around I am going to pre-soak the beans for 24 hours to speed germination. Will then plant the seeds in seed packs and will cover the seed packs in saran wrap so that the flies can't lay eggs in the soil. I just opened a brand new bag of potting soil, so the soil shouldn't be contaminated. However, if I still get maggots even when physically preventing eggs from entering the soil then I know my soil is contaminated and might try pouring boiling water over the soil to kill what is in it. If the soil isn't contaminated, then I should be passed the danger zone once the beans germinate and can plant them out (at least according to what I've read on the internet). I'm determined to have pole beans this summer!!!

I usually isn't recommended to SOAK bean for planting. There is apparently something about the rapid swelling that damages them.

My neighbor just told me that she got one of those fake chamois cloths, dampened it (not sopping wet), laid half of it in a pan, spread her bean seeds over it, then folded the other half over the beans and put it in a warm place, checking frequently on the moisture of the cloth.\

Sue

I found an online British article on them, and it indicates that preventive measures are the most successful:

* The flies like recently-cultivated soil, so prepare the beds about a month ahead of time, clear all weeds and keep them off.

* Get the seeds through the germination stage as quickly as you can.

* Don't incorporate organic matter just before sowing.

* Cover with a mesh fabric (Reemay is one) immediately after sowing.

* There is some indication that freezing the bean seeds will kill the maggots, but the flies still produce about four generations a year.

* Don't compost infested plants, either burn or securely bag/dispose.

Sue

Here is a link that might be useful: Bean seed flies/maggots