Why hoverflies prefer Sikkim flowers to those in Bengaluru

Study on pollination leads scientists to understand the brains of hoverflies; findings could hold key to protection of wild pollinators

If you were a hoverfly, part of a species that is among the most important pollinators in the world, flowers in Sikkim may perhaps be more attractive than even the ones found in Sweden or Bengaluru.

The simplest of the scientific questions — how does one of the most important pollination species in the world select its flowers — has lead to not only greater understanding of the pin-head-sized brains of hoverflies, but could also hold key to the protection of wild pollinators.

A global collaboration involving researchers from Uppsala University in Sweden, Flinders University in Australia, and the National Centre for Biological Sciences (NCBS) in Bengaluru set out to find these answers.

The teams led by Shannon Olsson (NCBS) and Karin Nordström (Uppsala University) followed hoverflies for months and patiently observed them.

The scientists tabulated the behaviour of hoverflies in tropical climes of outskirts of Bengaluru, mountainous northern Sikkim, and hemiboreal (landscapes close to the subarctic regions) of Uppsala, Sweden.

The observations — which were published recently in the journal, Proceedings of the National Academy of Sciences (PNAS) of the United States — showed that the tiny brains of hoverflies process multiple, complex factors to determine which flower they pollinate.

Crunching over a million data points, researchers found that combinations of visual clues (colour, shape, size), flower scents (more than 96 volatile chemical compounds) and immediate environment (humidity, carbon dioxide) determine attractiveness for, say Bengaluru hoverfly over its Swedish counterpart.

They then created artificial flowers (lures) based on what hoverflies in each place ‘liked’ to test their hypothesis.

The study found that ‘Sikkim lure’ worked well in other places, while, ‘Bengaluru lures’ were “less attractive” to hoverflies from other places.

Dr. Olsson hazarded a guess, “In Sikkim, the hoverfly is the major pollinator as bees do not thrive in high altitudes. Wild flowers developed ways to make them as universally attractive as possible. Whereas, in tropical Bengaluru, flowers have a choice of pollinators and do not have to try hard to attract hoverflies in particular.”

Hard to find in Bengaluru

During the study, the team realised that hoverflies were hard to find in urban Bengaluru, leading to the start of research to find the link between hoverfly populations and air pollution.

The study, says Dr. Olsson, can give insights on reversing the decline of wild pollinators, which are critical to the nearly $577-billion worth of crops globally.

“There is a thought on creation of pollination gardens and other spaces to revive pollinator populations. But, these ideas cannot be broad-based, because what works for European insect pollinators will not work in India. Studying these difference will help,” she said.

While arresting the decline in pollinator population will need lowering the use of pesticides, decreasing monoculture agricultural practices, and increasing natural vegetation, Dr. Nordström said, “It is also incredibly important to understand the natural ecology of wild pollinators, not just hoverflies, so we can make informed choices when planning strategies.”