The ground nesting bee Melissodes thelypodii Ckll, reportedly often forages on cotton (Gossypium spp.). It is endemic to Central America, Mexico, and Southwestern United States, which coincides with the distribution of wild cottons. In 1984, the emergence was in good synchrony with cotton flowering and a total of 47 bees emerged in a 120 m cage installed above cultivated land. To evaluate the pollination effectiveness of this species, twenty individuals (ten of each sex) were introduced between July 27 and August 1 into half a 120 m² screen cage planted with male-sterile(MS) and male-fertile (MF) upland cotton. The other half of the cage was provided with a colony of honey bees (Apis mellifera L.) fed only limited amounts of pollen supplement.

After four weeks, three individuals were still actively foraging, and at least one female had successfully nested and provisioned four cells with cotton pollen. The Melissodes bees started foraging on cotton immediately after their introduction into the cage Based on four dates of tagging, the MS flowers set an average of 32% bolls while the boll set was only 2% in the area serviced by honey bees. Three weeks after introduction, the geometric average of the pollen load on male-sterile stigmas was 35 for the Melissodes cage and 15 for the honey bee cage (p<0.001). Overall, 15 times more seed cotton was harvested on the male-sterile plants exposed to Melissodes than we harvested from the male-sterile plants exposed to the honey bee colony with limited pollen feeding (372 vs 25 g/10 m-row) The boll set (4.1 vs 0.6 bolls/plant) and the boll weight (3.33 vs 1.45 g/boll) also indicated that the Melissodes bees visited the cotton flowers more often nd transferred pollen more efficiently than did the honey bees. These results demonstrated that (1) M. thelypodii bees were effective pollinators for hybrid cotton seed production, and (2) under cage conditions, twenty individuals could set more bolls than a caged honey bee colony with limited pollen feedings.