Components of pollinator "quality": comparative analysis of a diverse insect assemblage

A total of 34 floral visitors of Lavandula latifolia (Labiatae) at a southern Spanish locality were examined from the perspective of their "quality" as pollinators. I considered frequency of pollen transfer, number of pollen grains deposited on the stigma, selection of floral sexual stage (flowers are markedly protandrous), and patterns of flight distance between flowers. Hymenoptera deposited more pollen and more often than Lepidoptera or Diptera. The latter two groups did not differ in this respect. Interspecific variation in frequency of pollen delivery depended on difference~ in proportional visitation to female-stage (receptive) flowers as well as total pollen delivery to these flowers. Lepidoptera tended to fly longer distances between consecutive flowers than Hymenoptera. Hand-pollination experiments demonstrate that variation among floral visitors in reproductive services rendered may translate into differential fitness of L. latifolia plants. Nevertheless, the potential for plant specialization on specific insects is constrained by counterbalancing variation in components of pollination quality.