CATCH THE BUZZ – Where have all the insects gone?
FROM: Science magazine:
<<The Krefeld Entomological Society, has seen the yearly insect catches fluctuate, as expected. But in 2013 they spotted something alarming. When they returned to one of their earliest trapping sites from 1989, the total mass of their catch had fallen by nearly 80%. Perhaps it was a particularly bad year, they thought, so they set up the traps again in 2014. The numbers were just as low. Through more direct comparisons, the group—which had preserved thousands of samples over 3 decades—found dramatic declines across more than a dozen other sites.
Between 1970 and 2002, the biomass caught in the traps in southern England did not decline significantly. Catches in southern Scotland, however, declined by more than two-thirds during the same period. Bell notes that overall numbers in Scotland were much higher at the start of the study. “It might be that much of the [insect] abundance in southern England had already been lost” by 1970, he says, after the dramatic postwar changes in agriculture and land use.
The stable catches in southern England are in part due to constant levels of pests such as aphids, which can thrive when their insect predators are removed. Such species can take advantage of a variety of environments, move large distances, and reproduce multiple times per year. Some can even benefit from pesticides because they reproduce quickly enough to develop resistance, whereas their predators decline. “So lots of insects will do great, but the insects that we love may not,” Black says.
Other, more visible creatures may be feeling the effects of the insect losses. Across North America and Europe, species of birds that eat flying insects, such as larks, swallows, and swifts, are in steep decline. Habitat loss certainly plays a role, Nocera says, “but the obvious factor that ties them all together is their diet.”
Some intriguing, although indirect, clues come from a rare ecological treasure: decades’ worth of stratified bird droppings. Nocera and his colleagues have been probing disused chimneys across Canada in which chimney swifts have built their nests for generations. From the droppings, he and his colleagues can reconstruct the diets of the birds, which eat almost exclusively insects caught on the wing.
The layers revealed a striking change in the birds’ diets in the 1940s, around the time DDT was introduced. The proportion of beetle remains dropped off, suggesting the birds were eating smaller insects—and getting fewer calories per catch. The proportion of beetle parts increased slightly again after DDT was banned in the 1970s but never reached its earlier levels.
Paying attention to what E. O. Wilson calls “the little things that run the world” is worthwhile, Sorg says. “We won’t exterminate all insects. That’s nonsense. Vertebrates would die out first. But we can cause massive damage to biodiversity—damage that harms us.”>>