Weaver ants help flowers get the best pollinator

MOST flowers don't want pesky ants hanging around scaring away would-be pollinators. Not so the Singapore rhododendron - the first flower found to recruit ants to chase poor pollinators away.

Francisco Gonz?lvez at EEZA, the arid zone experimental station in Almeria, Spain, and colleagues studied flowers frequented by large carpenter bees (Xylocopa) and a much smaller solitary bee, Nomia. The larger bees seemed to be better pollinators - setting far more fruit than the smaller bees.

The team found that Nomia avoided plants with weaver ant patrols, and when they did dare to land, were chased away or ambushed by the ants. Being so much bigger, carpenter bees weren't troubled by the ants (Journal of Ecology, DOI:10.1111/1365-2745.12006).

Plants usually produce chemical repellents to scare off insects that prey on their pollinators. But lab tests suggested Gonz?lvez's flowers were actively attracting weaver ants, although how remains a mystery. The team thinks carpenter bees choose flowers with ants so they don't have to compete with Nomia.

Michael Kaspari of the University of Oklahoma in Norman says this is a new kind of plant-ant interaction, and that the team makes a "strong case" for the rhododendron manipulating the behaviour of weaver ants to ward off inefficient pollinators.

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