All sorts of insects are in the process of disappearing, and this catastrophic change is happening so quickly that scientists can't keep up. The situation becomes even more tricky when you consider that insects have a complex life cycle that includes eggs, larvae, pupae and adults. Are they disappearing at the same rate, or are some faster than others? Very few people have done research.
In a new study, researchers present the results of a year-long survey in which they monitored the population of adult and larvae of moths in subtropical urban environments. This is the first time researchers have analyzed multiple life stages of insects to assess the severity of the ongoing decline in insect populations. It is also one of only a few studies that address the problem at low latitudes, where extreme temperatures are pushing animals to their limits.
"Subtropical and tropical environments have the largest and most abundant insect populations and are also the fastest growing regions in the world," said Michael Belitz, the study's lead author, who conducted the study while working at the Florida Museum of Natural History. "The urban heat island effect in these areas can be particularly harmful to insects".
Modern cities have a heat problem, no matter where they are located. In a natural or rural setting, a large part of the sun's light is harmlessly reflected back into space. But asphalt and concrete absorb more light and convert it into heat. During the day, this can make the city 7 degrees Fahrenheit warmer than the surrounding area, creating dangerously hot bubbles known as heat islands (heat domes), which can have disastrous consequences for those trapped in low latitudes where temperatures are already high.
"There is no doubt that the decline in insect populations is a real phenomenon. The harder question to answer is, where is the region where insect populations are declining the fastest?" said Robert Guralnick, director of biodiversity informatics at the Florida Museum of Natural History.
Due to habitat loss and pollution, moths are declining at an alarming rate in urban areas. Source: Florida Museum of Natural History. The basemap comes from OpenStreetMap, an open database license.
To find out, the team devised a survey to collect moths at several sites with varying levels of development in Aragua, Florida. Catching adult moths was easy, and the team members only needed a light source to lure them in. Caterpillars, on the other hand, are not attracted to artificial light sources and spend most of their time in the canopy, making them difficult to spot. But moth larvae are an important part of natural and urban ecosystems, and Beilitz is reluctant to exclude them.
"Caterpillars are an important food source for breeding birds," he said. "Even if birds only eat seeds as adults, they feed their young caterpillars. "
Although the caterpillars are out of our sight most of the time, there is at least one way to estimate their numbers: their droppings! Belize placed a funnel under the tree at each location, and the funnel was connected to the collection bottle. By weighing the amount of feces that fall into it each week, he has a rough estimate of the number of caterpillars.
By the end of the year, they had collected more than 35,000 moths and divided them into two categories: large and miniature moths. The first category includes well-known species like the moon moth and demoiselle moth, which have relatively large wings and are able to fly long distances. Miniature moths - This refers to moths with a body length of 10 mm or less, including numerous leaf-curling moths, grass moths, and cape-like wings in unbelievable beige and brown colors.
The distinction between large and small is important. Larger moths are better able to navigate fragmented habitats, and are more likely to escape from the Heat Dome if it gets too hot. Micromoths can only move in smaller areas, which may make them more susceptible to temperature fluctuations.
Large peacock moths used to be common throughout eastern North America, but their numbers have since decreased due to urbanization and other reasons. Image credit: Andrei Sourakov
The results showed a significant reduction in moths of all body sizes and life stages, from rural to urban areas.
A closer look at the moth's whereabouts revealed that, contrary to expectations, larger moths performed worse than smaller ones. This is the exact opposite of a previous study conducted in Belgium.
Bellitz suspects that the difference in average temperature between temperate Europe and subtropical Florida is to blame. Large moths have to expend more energy to keep their temperatures cold as compared to their smaller sizes. A similar pattern has been seen in other insects, Bellitz said.
They also found that moths with a varied diet were better suited to city life than those with a mild taste. Some caterpillars feed on a single species of plants, and when an area is developed, these caterpillars are the first to disappear. Moths, whose larvae feed on a variety of different plants, are more resilient to urbanization.
Most worryingly, the team only took samples in the protected area, but still observed a significant decline. "When you walk into a city park, you might think you're looking at a natural environment because it looks intact," Gulanik said. In fact, what you see is a completely different community than places like wildlife management areas."
Aragua County is also relatively underdeveloped compared to the rest of Florida. In an area with hundreds of acres of protected land, the domino effect of biodiversity loss bodes badly for other cities.
"In a city that is not very urbanized, the magnitude of these declines is staggering," Gulanik said. We're talking about town size, not a city like New York."
But Bellitz said that nothing had lost hope. Moths and other insects still survive on the fringes of cities, and increasing their numbers is in some ways as simple as creating the right environment for them, and this is something anyone can do.
"Native plants are an important way to increase biodiversity," he said. "The number of pollinators in the yard can be increased by planting host plants. Gulanik
Light pollution in urban environments can also disrupt the internal navigation systems of many insects. "It creates eco-traps where moths are attracted to lights and then preyed upon by bats. Lights out at night is a really actionable thing that people can do and has a great positive impact on insects and other animals."
编译来源：ScitechDaily