by Air pollution alters fruit fly mating behavior, with males forming flirtatious same-sex conga lines because they can no longer sniff out females, scientists have found.
Experts have found that high levels of ozone destroy chemical mating signals, making the confused insects difficult to bond with a suitable mate.
Scientists at the Max Planck Institute for Chemical Ecology in Germany said the finding could also apply to other species, such as bees and butterflies, and could be contributing to global insect die-offs.
Pollinating insects are critical to crops but have declined in recent decades, with habitat loss and pesticides blamed for the decline.
“We knew that elevated ozone levels could affect insect mating systems,” said researcher Dr. Nanji Jiang.
“Nevertheless, we were shocked that even slightly increased ozone concentrations had such a strong impact on the behavior of the flies.
“We were quite surprised by the behavior of the ozone-exposed males, who lined up in long courtship chains.
“The males began courting each other after a brief exposure to ozone because they apparently could not distinguish ozonated males from females.”
Pheromones are species specific
Insects rely heavily on pheromones — chemicals that distinguish males from females and encourage sexual behavior — when they want to mate.
Pheromones are highly specialized for individual species, and even a slight change can prevent sex finding.
Most insect pheromones are made from doubly bonded scent molecules, but the bonds that hold pairings together are easily destroyed by air pollution.
“We already knew that environmental pollutants like ozone and nitric oxide degrade floral odors, making flowers less attractive to their pollinators,” said Dr. Markus Knaden, who heads the Scent Controlled Behavior group in the Department of Evolutionary Neuroethology.
“Since compounds with carbon double bonds are particularly sensitive to ozone degradation and almost all insect sexpheromones carry such double bonds, we wondered whether air pollution also affects how well females and males find and identify each other during mating.”
To study the effects, scientists exposed fruit flies to a continuous stream of air that was either clear or ozone-laden.
When male flies were exposed to 100 parts per billion ozone for two hours, their pheromone levels decreased significantly compared to the flies in fresh air.
Experts said the “most disturbing” change in behavior occurred in how men interacted with each other. Normally, male pheromones not only attract females but also repel other males.
Unusual courtship behavior
But scientists found that increased ozone levels not only reduced females’ attraction to males, but also caused males to start sniffing each other.
In eight of the other nine species studied, the research team observed unusual courtship behavior by males towards other males exposed to ozone.
Only one species, D. suzukii, which is known to have no pheromones and instead finds a mate based on visual cues, was not affected at all by elevated ozone levels.
Experts say the study provides an additional explanation for why insect populations are declining dramatically around the world, along with insecticide use and habitat destruction.
“All social insects, such as bees, ants, and wasps, use chemical cues to identify members of their colony,” said Dr. boys.
“You don’t even want to imagine what happens when social structures in ant colonies or beehives suddenly collapse because pheromone communication no longer works,”
The study was published in the journal Nature Communications.
