Honeybees facilitate the invasion of 'Phyla canescens' (Verbenaceae) in Australia - no bees, no seed!

Several environmental weeds rely on the pollination services of introduced bees. The transfer of this knowledge to weed control management has not been fully explored. In part, this may be because it is difficult to quantify the economic impact of environmental weeds. This diminishes the prospects for expensive research and development required for integrated weed management. In this study, we examine the reproductive ecology of 'Phyla canescens', a species native to South America that is an aggressive agricultural and environmental weed in many parts of the world. We found that 'P. canescens' is self-compatible, but not capable of automatic self-pollination. A vector is required to effect seed set. Field studies showed that 45% of seeds produced through open pollination are viable. Using exclosure cages, we showed that non-native 'Apis mellifera' L. (honeybee) was the primary floral visitor and pollinator. Honeybee abundance was positively correlated with P. canescens abundance. Within the study site of 0.51 ha, almost 500 000 seeds ha-¹ would be produced annually, as a result of honeybee pollination. This study shows that a shared evolutionary history is not required for honeybees to be successful pollinators. Facilitation is demonstrated through the obligate need for pollinators and the successful recruitment of the species through seed. Models for the control of feral honeybees in agricultural systems require development.