Puerto Rico’s Insect Population Is Dwindling, Too

A series of research reports from biologists worldwide has shown that the world’s insect population is falling sharply. A new report published in in the Proceedings of the National Academy of Sciences spotlights the same problem in Puerto Rico.

This is not the result of Hurricane Maria. The researchers had visited El Yunque, the tropical rainforest on the Island, in the 1970s, cataloging and counting insects. They recently returned to replicate their earlier work. In category after category, they saw startling drops in the populations: 30 percent, 60 percent, 90 percent.

Checking other research over the same time period, they saw similar results. Scientists measuring population change among insects before Hurricane Maria saw the same pattern.

Insects and other arthropods, from butterflies to spiders, are present in Puerto Rico in much smaller numbers than before.

Is insect loss a problem?

Thinking of the Zika virus and Dengue fever could make a drop in insect species seem like a good thing, or at least a mixed blessing. But insects are the base of the food chain. With fewer insects, there will be fewer reptiles, amphibians, and fish, fewer birds, and then fewer of the larger creatures that feed on the insect-eaters.

The researchers found that this is already visible in Puerto Rico. One insect-eating bird has decreased in population by 90 percent. Some species of insect-eating lizards could not be found at all.

Beyond the effects on the food web, a loss of insects has other likely consequences as well. Insects pollinate more than one third of all food crops. They clean up the environment, eating animal carcasses and leavings, rotting vegetation, and more. According to the Washington Post, insects provide $57 billion in labor each year in the U.S. alone.

What’s causing the problem?

The temperature in El Yunque has risen by four degrees Fahrenheit (about 2 degrees Celsius) since the 1970s. Equatorial insects live in a seasonless environment and cannot control their internal temperatures as mammals do. If the temperature varies too much, they stop laying eggs.

The temperature increase in the ocean (just 3 degrees) has been implicated in the increase in tropical storms and the increasing force of hurricanes. Computer models suggest that the same change in temperature is at fault in the massive insect population drop.

Other possibilities suggested in similar research in other parts of the world include loss of habitat and increased pesticide use. Neither of these appears to be an issue in Puerto Rico, where pesticide use has declined significantly since the 20th century. The area studied in this case is a protected area, and the insects’ habitat has not been threatened by human encroachment.

Problems of this kind are likely to show up first at the equator. Creatures that live in other parts of the world usually have greater ability to respond to variation in temperatures, because most parts of the world have hotter and cooler seasons. What is showing up in Puerto Rico now — and to a lesser extent in other parts of the world — foreshadows what other parts of the world may expect to see in the future.

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