higgledy said:

Should I spray a pesticide?

No.

Quoting: "No chemical control measures are available for home gardeners.
The use of entomogenous nematodes to treat the soil to help control seed
maggots may prove useful in some circumstances."

http://www.uoguelph.ca/pdc/Factsheet...eedMaggots.htm

Diazanon used to be recommended for home gardeners to use against
seed and root maggots but I do believe it has been withdrawn.

Organic controls would be those nematodes mentioned. A heavy dusting
of diatomaceous earth when planting the bean seeds might be useful.

You didn't mention where you are located, but if you are anywhere in
the northeastern US, the cool wet weather we had earlier in late May was
perfect for seed maggots. I lost some of my bean planting this year. It
happens.

Replant into warmer soil and you should be OK.
--
Pat in Plymouth MI ('someplace.net' is comcast)

Any technology distinguishable from magic is insufficiently advanced.
(attributed to Don Marti)