Global Decline of Insects and the use of Neonicotinoids

Peter J. Bryant, Newport Bay Conservancy

About three quarter of the species on this planet are insects: about 1 million species have been fully described and another 4 million or so are estimated to exist. However, alarming new data from many parts of the world suggests that they are declining rapidly. In California, it is difficult to separate the effects of our recent multi-year drought from a longer-term trend, but the losses are clear in other parts of the world. Some of the most revealing research comes from an analysis of insects collected at 63 locations in nature reserves supporting many different habitats in Germany. Between 1989 and 2016, the biomass of captured insects declined by an average of 76%.

Some of the declines are of the insects that are the most obvious and easiest to survey. Monarch butterfly populations have declined by more than 80% in central Mexico and 97% in coastal California. My surveys of the butterflies in Eastbluff, Newport Beach showed, in a one-day count carried out in July of each year, a reduction from over 500 individuals of about 16 species in the early 1990s to 14 individuals of 6 species in 2012. Google searches for the title "Where have all the butterflies gone" return links to newspaper articles with that title from Orange County, the Central Valley, Northern California, Pennsylvania, Minnesota, Washington, D.C., India, Canada, Japan, South Australia, and Britain.

Honeybee colonies have disappeared in huge numbers in both Europe and North America due to a phenomenon called Colony Collapse Disorder, but bumblebees are also in trouble. Bumblebees are better pollinators than honeybees for certain crops including tomatoes, pumpkins and blueberries because they are able to buzz-pollinate, which means they can hold on to the flower and vibrate it so violently that it releases large amounts of pollen. A Utah State University study published in 2011 showed that four species of bumblebees had declined by up to 96%. The Rusty patched Bumblebee, Bombus affinis, native to many states in the eastern half of the country, declined so much over the past 20 years that the U.S. Fish and Wildlife Service listed it 2018 as an Endangered Species. The Service also listed seven species of Hawaiian yellow-faced bees as endangered in 2017.

The beautiful Sonoran Bumblebee, Bombus sonorus, (also known as the American Bumblebee, Bombus pensylvanicus) photographed by Ron Hemberger at the UCI arboretum in 2010, has shown dramatic declines over much of North America, and has been recommended for listing as Vulnerable by the International Union for the Conservation of Nature. It was once very common in California's Central Valley, but has virtually disappeared there since about 2003.

Possible causes of the widespread decline of insects include the usual habitat destruction, urbanization, and overuse of insecticides. But during this decade there has been a rapid switch from traditional organophosphate and carbamate insecticides to a group of chemicals called neonicotinoids that act systemically (they are taken up into the entire plant). They work by affecting the central nervous system of the insect, leading to paralysis and death. These compounds now make up more than a quarter of the global insecticide market and are common components of insecticides used both commercially and for home gardening. One of them, imidacloprid, is now the most widely used insecticide in the world.  In agricultural applications such as corn, cereals and oilseed rape, neonicotinoids are usually applied as coatings to seeds. They are taken up systemically by the growing plant and distributed to all tissues including flowers, where they make both pollen and nectar toxic to pollinators and create a toxic trap. Honeybees, of course, are the main cause for concern because they are responsible for pollinating so many of our food crops. In 2014, an analysis of 1,121 peer-reviewed studies led to the conclusion that neonicotinoids are a leading cause of bee declines and are also harming earthworms, butterflies and other wildlife.

More alarming for many people is that the decline of insect populations means a loss of the food supply for insectivorous birds. In one of the most informative studies, over the period from 2003 to 2009 in the Netherlands, populations of insect-eating birds declined faster in those places that had more neonicotinoid pollution.

Concerns about their environmental impacts led the European Union in May 2018 to ban completely the outdoor uses of three neonicotinoids (imidacloprid, clothianidin and thiamethoxam). Two other neonicotinoids, acetamiprid and thiacloprid, are still approved since they have been shown to be less harmful to bees.

Some of our local plant nurseries and hardware stores have agreed to stop selling insecticides containing neonicotinoids and plants treated with them. As early as 2007, Roger's Gardens in Newport Beach stopped selling all neonicotinoids as well as carbamate and pyrethroid insecticides and other non-natural controls. Home Depot has announced that it will phase out the use of neonicotinoids in its plants by 2018, and Lowes is planning to phase out neonicotinoid-containing products in shelf products and plants by Spring of 2019.

In 2014, Jim Kurth, Chief of the National Wildlife Refuge System announced that by January of 2016, neonicotinoids will no longer be used on our National Wildlife Refuges. But this ban was revoked by the Trump administration in 2018, for the benefit of farmers and ranchers who are allowed to operate within the Refuges. The Center for Biological Diversity and the Center for Food Safety are planning to sue the Trump administration over the policy reversal.