Warning: dying insect populations threaten our future

Summary: While we obsess over climate change, other severe threats grow worse. Previous posts discussed our dying oceans. Today we look at the rapid decay in the health of insect populations. If it continues, this could have horrific effects.

“Vanishing Act: Why Insects Are Declining and Why It Matters“

By Christian Schwägerl in Yale360

“Insect populations are declining dramatically in many parts of the world, recent studies show. Researchers say various factors, from monoculture farming to habitat loss, are to blame for the plight of insects, which are essential to agriculture and ecosystems.”

“Every spring since 1989, entomologists have set up tents in the meadows and woodlands of the Orbroicher Bruch nature reserve and 87 other areas in the western German state of North Rhine-Westphalia. The tents act as insect traps and enable the scientists to calculate how many bugs live in an area over a full summer period. Recently, researchers presented the results of their work to parliamentarians from the German Bundestag, and the findings were alarming: The average biomass of insects caught between May and October has steadily decreased from 1.6 kilograms (3.5 pounds) per trap in 1989 to just 300 grams (10.6 ounces) in 2014.

“The decline is dramatic and depressing and it affects all kinds of insects, including butterflies, wild bees, and hoverflies,” says Martin Sorg, an entomologist from the Krefeld Entomological Association involved in running the monitoring project.

“…Another recent study has added to this concern. Scientists from the Technical University of Munich and the Senckenberg Natural History Museum in Frankfurt have determined that in a nature reserve near the Bavarian city of Regensburg, the number of recorded butterfly and Burnet moth species has declined from 117 in 1840 to 71 in 2013. “Our study reveals, through one detailed example, that even official protection status can’t really prevent dramatic species loss,” says Thomas Schmitt, director of the Senckenberg Entomological Institute.

Declines in insect populations are hardly limited to Germany. A 2014 study in Science documented a steep drop in insect and invertebrate populations worldwide. By combining data from the few comprehensive studies that exist, lead author Rodolfo Dirzo, an ecologist at Stanford University, developed a global index for invertebrate abundance that showed a 45 percent decline over the last four decades. Dirzo points out that out of 3,623 terrestrial invertebrate species on the International Union for Conservation of Nature [IUCN] Red List, 42 percent are classified as threatened with extinction.

“Although invertebrates are the least well-evaluated faunal groups within the IUCN database, the available information suggests a dire situation in many parts of the world,” says Dirzo.

A major survey of threats to insect life by the Zoological Society of London, published in 2012, concluded that many insect populations worldwide are in severe decline, limiting food supplies for larger animals and affecting ecosystem services like pollination. In Europe and the United States, researchers have documented declines in wild and managed bee populations of 30 to 40 percent and more due to so-called colony collapse disorder. Other insect species, such as the monarch butterfly, also have experienced sharp declines.

“Jürgen Deckert, insect custodian at the Berlin Natural History Museum, says he is worried that “the decline in insect populations is gradual and that there’s a risk we will only really take notice once it is too late.”

“Scientists cite many factors in the fall-off of the world’s insect populations, but chief among them are the ubiquitous use of pesticides, the spread of monoculture crops such as corn and soybeans, urbanization, and habitat destruction.

“A significant drop in insect populations could have far-reaching consequences for the natural world and for humans, who depend on bees and other invertebrates to pollinate crops. A study by Canadian biologists, published in 2010, suggests that North American bird species that depend on aerial insects for feeding themselves and their offspring have suffered much more pronounced declines in recent years than other perching birds that largely feed on seeds.

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Two studies mentioned in this article

(1)  “Defaunation in the Anthropocene” by Rodolfo Dirzo et al, Science, 25 July 2014. Ungated copy here. Abstract followed by an excerpt…

“We live amid a global wave of anthropogenically driven biodiversity loss: species and population extirpations and, critically, declines in local species abundance. Particularly, human impacts on animal biodiversity are an under-recognized form of global environmental change. Among terrestrial vertebrates, 322 species have become extinct since 1500, and populations of the remaining species show 25% average decline in abundance. Invertebrate patterns are equally dire: 67% of monitored populations show 45% mean abundance decline.”

“Such animal declines will cascade onto ecosystem functioning and human well-being. Much remains unknown about this “Anthropocene defaunation”; these knowledge gaps hinder our capacity to predict and limit defaunation impacts. Clearly, however, defaunation is both a pervasive component of the planet’s sixth mass extinction and also a major driver of global ecological change.”

“Loss of invertebrate biodiversity has received much less attention, and data are extremely limited. However, data suggest that the rates of decline in numbers, species extinction, and range contraction among terrestrial invertebrates are at least as severe as among vertebrates.

“Although less than 1% of the 1.4 million described invertebrate species have been assessed for threat by the IUCN, of those assessed, ~40% are considered threatened. Similarly, IUCN data on the status of 203 insect species in five orders reveal vastly more species in decline than increasing (Fig. 1A). Likewise, for the invertebrates for which trends have been evaluated in Europe, there is a much higher proportion of species with numbers decreasing rather than increasing.

“Long-term distribution data on moths and four other insect orders in the UK show that a substantial proportion of species have experienced severe range declines in the past several decades (Fig. 1B).

“Globally, long-term monitoring data on a sample of 452 invertebrate species indicate that there has been an overall decline in abundance of individuals since 1970 (Fig. 1C). Focusing on just the Lepidoptera (butterflies and moths), for which the best data are available, there is strong evidence of declines in abundance globally (35% over 40 years) (Fig. 1C). Non-Lepidopteran invertebrates declined considerably more, indicating that estimates of decline of invertebrates based on Lepidoptera data alone are conservative (Fig. 1C).”

(2)  For more detail see “Spineless: Status and trends of the world’s invertebrates” by the Zoological Society of London (2012).

For More Information

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• Are 30 thousand species going extinct every year?