Flowers Invite Weaver Ants to Chase Off Poor Pollinators

A new study has found that Singapore rhododendron flowers use ants to scare off poor pollinators, New Scientist reports.

Singapore rhododendron (Melastoma malabathricum) is a flowering plant that belongs to the family of Melastomataceae. The plant is also called as Malabar Melastone or Indian Rhododendron.

It is commonly found in countries like China, Japan, India, Malaysia, Thailand and Indonesia, and is used as a medicinal plant in some countries.

While plants are known to fend off insects like ants that trouble pollinators, the Singapore rhododendron is the first flower found to invite weaver ants. 

A team of researchers led by Francisco Gonzálvez, from Estación Experimental de Zonas Áridas in Almería, Spain, examined flowers visited by larger carpenter bees (Xylocopa) and smaller bees Nomia. The larger the bees, the better pollinators they are. But smaller bees are poorer in pollination.

During their observation, the research team noticed that the Nomia bees avoided pollinating in flowers that were visited by weaver ants. Those bees that dared to pollinate in the flowers were attacked by the ants. However, the bigger bees, like carpenter bees, were not troubled by the ants.

Plants release chemical repellents to chase off insects that trouble the pollinators. But lab tests carried out by the research team revealed that the Singapore rhododendron flowers attracted ants, but how it does is still not known. They suggest that the flowers invite ants to ward off incompetent pollinators.

Researchers also noticed that carpenter bees preferred to pollinate in flowers that had ants. They believe that the bees are behaving this way to avoid competition with Nomia bees.

This type of plant-ant interaction "makes a 'strong case' for the rhododendron manipulating the behavior of weaver ants to ward off inefficient pollinators," Michael Kaspari, of the University of Oklahoma in Norman, told New Scientist.

The findings of the study are published in the Journal of Ecology.