Structural and Functional Co‐Adaptation of Plants of the Genus <i>Lysimachia</i> L. (Primulaceae) and Pollinating Insects of the Genus <i>Macropis</i> Panzer (Hymenoptera, Melittidae)

The pollination system 'oil-collecting bees <i>Macropis</i> and oil-producing plants <i>Lysimachia</i>', probably originated a long time ago. Although much is already known about the biology and ecology of this fascinating interaction, we reveal here features of the structural elements of the secretory system of the <i>Lysimachia</i> flowers and the foraging behaviour of <i>Macropis</i> bees. A model describing the process of collecting flower oil by bees based on the laws of mechanics is presented. The model considers the histochemical and morphological features of the secretory apparatus in <i>Lysimachia</i> flowers, as well as the behaviour and micromorphological structure of the oil- and pollen-collecting apparatus of the bee. All these structures seem to be adapted for collecting flower oil and other metabolic products, demonstrating a process of co-adaptation. It has been clarified for the first time that <i>Macropis</i> females do not merely collect pure floral oil through capillary absorption or by mopping up oil from trichomes on the flower stamens and petals via specialised pubescence on the fore- and mid-tibia and tarsi of bees, as was previously thought. Instead, they collect entire oil-filled trichome heads by breaking them off from the trichome stems. A neck (intermediate) cell has been described in the oil-secreting capitate trichomes of <i>Lysimachia nummularia</i> L. The dominance of pectin and hemicellulose in its cell walls, combined with high beta-galactosidase activity during trichome maturation, creates conditions for the formation of a microabscission zone. This zone facilitates the detachment of the oil-containing capitate when contact occurs with pollinating bees of the genus <i>Macropis</i>.