Every year millions of monarch butterflies (黑脉金斑蝶) in the US and southern Canada search for milkweed plants on which to lay their eggs. Concern over reduced habitat has pushed conservationists to create monarch-friendly spaces along roadsides, which are abundant within the butterflies' range and usually publicly owned. But traffic noise stresses monarch larvae (幼虫) out, a new study finds , which might spell trouble for them later on, too.
Andy Davis, a conservation physiologist at the University of Georgia, noticed online videos of roadside monarch larvae apparently shaking as cars zoomed by. He wondered how the constant loud noise might affect them. Davis built a custom larva heart monitor, fitting a small sensor into a microscope to precisely measure monarch larvae' heart rates as they listened to recordings of traffic sounds in the laboratory.
The hearts of larvae inundated with highway noise for two hours beat 17 percent faster than those of larvae in a silent room. But larvae eventually do become desensitized (脱敏的,麻木的) to noise. This desensitization could be problematic when the larvae become adults, Davis says. A rapid stress response is vital for monarch butterflies on their two-month journeys to spend winters in Mexico, as they narrowly escape predators and fight wind currents. "What I think is happening on roadsides is that their stress reactions get overwhelmed(压垮) when they're larvae and could be damaged when they travel to Mexico,"" Davis says.
Whether a noisy larval period reduces monarchs' survival rates remains unknown, notes Ryan Norris, an ecologist at the University of Guelph in Ontario, who was not involved in the study." But in any case, monarch-friendly spaces along roadsides almost certainly drive up the butterflies' death rate as a result of collisions with cars. There is so much potential road habitat for monarchs and other insects一it would be such a nice thing to make use of," Norris says." But you just can't get around the traffic.