Nectar robbing by bees on the flowers of Volkameria inermis (Lamiaceae) in Coringa Wildlife Sanctuary, Andhra Pradesh, India

Floral traits that shape the floral architecture are important to allow or disallow flower visitors to access nectar and effect pollination. Specialization in floral architecture is vulnerable to flower visitors that exploit nectar by robbery without effecting pollination. In Coringa Wildlife Sanctuary in Andhra Pradesh, India, studies on the exploitation of nectar by robbery in plant species with specialized flowers are completely lacking. We carried out a study on the foraging activity of insect foragers and nectar robbing by bees on the specialized nectariferous flowers of an evergreen shrub, Volkameria inermis growing in the landward side of this sanctuary. Field observations indicated that the flowers of this species facilitate legitimate probing only by butterflies and diurnal moths which while seeking nectar effect pollination. However, two bee species Anthophora dizona and Xylocopa pubescens seek nectar illegitimately as primary nectar robbers by making a slit/hole into the corolla tube from outside bypassing the flower front. Additionally, A. dizona gathers pollen legitimately from the stamens which are exposed and placed outside the corolla tube. The stigma is also placed outside the corolla tube but this bee indiscriminately makes attempts to collect pollen from the stigma, as a result of which pollination occurs. Nectar robbing by these bees leads to a reduction in nectar volume in robbed flowers and brings about variability in the standing crop of nectar. As a result, the pollinating butterflies increase the number of nectar foraging visits and shuttle between populations of V. inermis in quest of more nectar to meet their daily metabolic requirements. Such a foraging behavior increases pollination rate in general and cross-pollination in particular, which in turn increases plant fitness in V. inermis. Therefore, the nectar robbing by bees appears to have a positive effect on plant fitness through change in seed set rates.