Pollination ecology of Lantana camara and its relationship with honey bees (Apis mellifera scutellata) in South Africa

Abstract

Invasive species are considered a major biological threat to the planet, causing losses on economic and environmental fronts. Lantana camara is one of the worst invasive plant species, globally and in South Africa, with the cost of control of lantana amounting to millions of rands annually. The success of invasive plants, including lantana, is often dictated by the presence of potential, often native, pollinators in newly invaded environments. Shared pollinators are also an important way in which invasive plants interact with sympatric, coflowering native plant species. Pollinator preferences can influence the success of natives and invasives in a shared environment. This study aims to investigate the pollination ecology of Lantana camara in South Africa, specifically focusing on African honey bees (Apis mellifera scutellata), and how lantana interacts with three native flowering plant species, Aloe greatheadii, Aloe marlothii, and Kalanchoe rotundifolia, via their shared native pollinators. The diversity of flower-visitors of lantana in an urban nature reserve was explored in four sampling seasons (spring, summer, autumn, and winter, from Nov 2021 to Jun 2022). We show the pollinator population utilising lantana is diverse (31 families from 5 orders) and the main pollinators of lantana in our study sites are thrips. Honey bees were the second most abundant pollinators. The variation in the number of honey bees observed on lantana was only explained by observation season. We were further interested to see how different pollinators influence the pollination success of lantana. This was accomplished with exclusion experiments, designed to exclude pollinators based on size. We found no significant differences in the numbers of viable fruits produced by lantana between the different exclusion treatments. To investigate the potential impact of lantana on indigenous flowering plants two experiments were conducted to investigate the preferences of native pollinators at a species level and a community level. For the species-level experiments, preference experiments were conducted on African honey bees. Honey bee colonies were presented with a choice between lantana and two indigenous bee plants, Aloe greatheadii and Aloe marlothii. These data show that honey bees chose aloes significantly more often than lantana, and took less time to choose vi Abstract aloes, indicating a preference for the indigenous plants. At a community level, pollinator communities on the indigenous Kalanchoe rotundifolia in the inflorescences were compared between plots invaded with Lantana camara and those where the lantana had been removed. No differences in the pollinating communities of invaded plots versus cleared plots were found. Post hoc analysis revealed that the power of the statistical analysis is not high enough to confidently reject the alternative hypothesis that lantana influences the number of pollinators per observation bout between the cleared and invaded sites. Improvements to the study design are discussed. This study provides insights into the interaction of native South African pollinators with Lantana camara and to what extent lantana relies on these interactions for successful fruit production. Many native pollinators utilize the resources provided by lantana, which likely contributes to its success in South Africa. Honey bees, however, are not at the forefront of this success, showing a clear preference for indigenous aloes.