Abstract:

Thermopsis lanceolata is sand-fixing plant that plays an important role as a spring nectar source in northeastern China; however, little is known about its reproductive characteristics. To ascertain the major pollinators of T. lanceolata, we identified foraging behaviors, pollination process, activity rhythm of floral visitors and the effect of nectar robbers on the seed setting were investigated in Mu Us Sandland, Inner Mongolia. We used photo, video and visual measurement to observe floral visitors in a 10 m × 10 m quadrat. We recorded the species, pollinating behaviors and visiting frequency of all pollinators from 06:00 hours until 19:00 hours in sunny days. Based on visitation frequencies and pollen amounts carried on the body, two bee species, Megachile japonica and Hoplitis princeps were identified as the primary pollinators of T. lanceolata., but visiting frequencies between the two species were significantly different. Daily activity of M. japonica was bimodal with diurnal foraging activities during 9:00-13:00 and 16:00-18:00 hours, whereas daily activity of H. princeps was of unimodal type from 11:30 to 16:30 hours. We also noted nectar robbing behaviors by M. japonica due to the presence of nectar acquisition holes at the base of the flower of T. lanceolata, but found that these behaviors had no effect on seed setting. Pollinator activity peaks indicate a complementary relationship between M. japonica and H. princeps. Our observations of visiting frequencies suggest that M. japonica was a dominant pollinator for T. lanceolata.

Key words: Thermopsis lanceolata, pollinators, foraging behavior, nectar-robbing, visiting frequency