Table 1.

Summary of sampling schemes and sources for available bumble-bee studies in red clover seed fields 1942–2010.

period	years	number of fields visiteda	sampled area per visit (m2)	number of visits to each field in a season	average number of bumble-bees per year and fieldb	source
1940s	1942	7	25	10–20 daily	1140	[14]
	1943–1946	10	100–400	2–3 daily	2439	[14]
	1949	1	—	—	1440	[15]
1960s	1959–1960	11	—	—	—	[16]c
	1961	16	—	—	—	[17]c
	1962	1	—	—	7142	[18]
	1962	1	100–200	1	—	[19]c
present	2008	14	200	2	234
	2009	41	100	3–5	118
	2010	28	100	3–5	58

^aSome fields were revisited in several years.

^bAverage total number of bumble-bees recorded in a field over a season.

^cOnly proportional species composition (not abundances) are reported.