Pollution vs pollination: Bugs losing battle to filthy air

  • Living
  • Wednesday, 02 Jul 2014

Scientists are discovering that human-made air pollution is meddling with the 'noses' of pollinating insects, which may have adverse effects on our food supply.

You think your nose likes flowers? Well, certainly not as much as the tobacco hornworn moth (Manduca sexta). In fact, its life depends on it. These moths, whose olfactory abilities are as good as a bloodhound’s and vastly better than a human's, can fly up to 130km a night searching for their favourite flowers such as the Sacred Datura (Datura wrightii). 

The nectar of these fragrant white, trumpet-shaped flowers that bloom only once at night is an important food source for the moths, which pollinate the flowers. Females also go to the flowers to lay eggs. After hatching, the larvae eat the plant’s leaves.

Scientists have wondered how pollinating insects such as these moths track down the flowers they need and whether competing odours — natural and manmade — can mess things up.

In a study published on June 27 in Science, researchers describe how they placed the moths in a laboratory wind tunnel and exposed them to an array of odours such as car and truck exhaust fumes and fragrances of other plants. Human sources of pollution fouled up their ability to find flowers and changed how the flower's scent was processed by olfactory neurons in the moth’s brain.

"Pollinators like bees, butterflies and moths use their sense of smell to locate flowers from long distances, but we found that scent from neighbouring vegetation, and even pollutants given off from vehicle exhaust, can disrupt the moth’s behaviour," University of Washington biology professor Jeffrey Riffell said.

"Now for the moths that are flying long distances, they can't adequately smell the flowers and at times won’t even know the flowers are there," Riffell added. "We really need to conduct more experiments to find out if these pollutants, or even certain plants, might similarly disrupt other pollinators, like honeybees, that are agriculturally important."

The tobacco hornworm moth — a large, nocturnal insect with a wingspan of about 10cm — ranges from Canada to Central America, including across the US. In the US Southwest, their favoured flower is the Sacred Datura, also known as angel’s trumpets.

In a wind tunnel and a computer-controlled odour-stimulus system, the moths were tested to see how well they could distinguish different intensities of Sacred Datura fragrance, as well as mixes of background odours from other plants such as the creosote bushes that often grow nearby. The researchers also piped in chemicals such as those emitted in vehicle exhaust.

The researchers tracked the neuron pathways activated by placing an electrode into the moth’s antennal lobe. The antennae serve as an insect’s nose. The antennal lobe is the part of the brain that processes odours from the antennae.

The moths can zero in on flowers hundreds of metres away if there are not too many competing odours. Such odours mess with the balance of excitation and inhibition in the olfactory system, keeping the moths from recognising the flowers.

"The total combination of dynamic odours, including floral signature odours as well as anthropogenic pollutants, can affect the success of olfactory-based resource finding," University of Arizona researcher Leif Abrell added. — Reuters

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