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Declining Insects — Declining World: Part 2 Causes of Insect Decline

By: Sandra Nelson; Images Sandy DeFoe

Insect populations around the world are rapidly declining. Within the next 20 years, 40% of the earth’s insect species may be extinct and within 100 years insects could disappear completely.  (Blog intro: Declining Insects —  Declining World, Feb. 20, 2019)


As usual, once I start thinking about a topic, it pops up everywhere; declining insect populations is no exception. I was scrolling through some news briefs over the weekend and an article about  bugs jumped out at me. The information was timely, but it was a quick anecdote that caught my attention.




The author talked about having to clean squashed bugs off of the windshield after taking long car trips. It made me remember standing beside gas pumps, washing the remains of bugs off of our car windows when we traveled to Colorado for vacations…and I realized that I haven’t had to scrub bugs for years. Logically, I realize that this is not scientific, research-based evidence of insect decline, but in my heart it is strong documentation of a problem.



Last week we looked at the benefits that a healthy and diverse insect population brings our planet. This week, I’d like to examine some of the reasons that, according to scientists and researchers, the world is losing large numbers of insect species.

Although experts in fields such as entomology, biology and environmental studies have identified multiple factors that contribute to the decline, there is a consensus that four major aspects are involved: commercial monoculture agriculture, pesticide use, urbanization/habitat destruction and climate change.


Commercial Monoculture Agriculture



Commercial, monoculture agriculture, also known as intensive agriculture, changed not just the techniques and goals of farming, but the look of the farms as well. Historically, smaller farms producing a variety of crops in a variety of fields each season and raising livestock primarily for individual needs was the norm. Fields were often separated by uncleared patches of naturally occurring trees, shrubs and grasses. These fencerows, as they were commonly called, served several purposes, one of which was as a home environment for beneficial insects, birds and other wildlife.



After the Great Depression, the number of farms fell sharply and farmers became a small percentage of the overall labor force. With fewer farms and farmers, commercial farming — raising a single crop to sell for profit — began to emerge. The thinking was that by concentrating on a single crop, farmers could more precisely tailor their fertilizing, weed control, irrigation and harvesting practices as well as their pest control to the needs of one crop and thus save time and money.



By the 1970s commercial farming and its monoculture practices had become entrenched in the United States. The size of the average farm doubled to 434 acres (USDA, 2018).and  60% – 80% of the 2+ million United States farms produced only a single crop. The fields themselves became larger, more suited to the efficient use of powerful equipment. Fencerows, thought to be unnecessary, became a hindrance and were eliminated as “big” farming took root in the country. The wildlife, including the insects, lost their homes.



While the basic premises of monoculture farming were true, some fundamental environmental issues also evolved. One concerned insect populations; monoculture saw the diversity of insect populations diminish. The number of insects preying on the crop increased and the numbers of their natural insect predators decreased. In order to protect yields, farmers had to apply more and stronger chemicals to kill the unwanted pests.


Pesticide Use



Pesticide use is not a new phenomenon. Records show that the Sumerians used sulphur compounds for insect control over 4000 years ago, and the Greeks and Romans were familiar with using organic compounds for pesticides.



Here in the United States, the search for highly effective pesticides began in earnest during the latter part of the 1930s. Prior to the advent of monoculture, insect infestations had been a relatively minor problem but miles of an uninterrupted favorite food buffet changed that. Highly toxic to humans but only mildly effective on insects, pesticides based on arsenic, copper and lead came on the market. They were used, but better alternatives were demanded.



Research for more effective pesticides continued through the 40s and 50s. Broad spectrum synthetic pesticides like 2,4-D and DDT were introduced by the chemical companies and embraced by the public who viewed them as safer and considerably more effective than arsenic based alternatives. Because they were seen as “safe” and there was little public awareness of any long-term hazards, a mentality of indiscriminate use of pesticides became commonplace.



Rachel Carson, in her best-selling book The Silent Spring (1962), began the push for environmentally sound insect control practices. She was among the first to try to alert the public to the secondary dangers of harsh chemical pesticides. Research continued and new families of pesticides were born in the 70s, 80s and 90s that were touted as being much more selective in their kill patterns.



Currently neonicotinoids, a family of pesticides related to nicotine, are the most used pesticides worldwide. They are relatively non-toxic to humans and were originally hyped as being safer for birds and beneficial insects. Unfortunately, just like other classes of pesticides, the claims of safety are being questioned. Research studies are suggesting that these pesticides contaminate nectar and pollen which then in turn causes problems with bees and other pollinators. The insects are unable to successfully forage for nectar or navigate back to their hives. A decrease in some bird populations has also been linked to neonicotinoids.


Urbanization/ Habitat Destruction



Insect and animal habitats worldwide are being lost  at an unprecedented rate. The 2018 Living Planet Report, published by the World Wildlife fund indicates that only one quarter of the earth’s land remains untouched by human intervention. As an example, this year alone, China is backing at least 7,000 new development projects in 70 different countries, including building a gigantic hydroelectric dam and a multitude of new roads designed to reach and extract natural resource deposits. (Scientific American)



Just like the rest of the world, habitats in the United States are at risk.. Approximately 47% of our total 2.3 billion acres of land area is covered by primary and secondary urbanization, or cities, suburbs, small towns, roadways, airports etc. Since urbanization continues to grow at about 1 million acres every year, that means more natural areas are changed into residential communities, commercial areas, schools, roads and other infrastructure needs every year.  



While on the surface it appears that a significant amount of our land is left as undeveloped grasslands, wetlands and waterways, the truth is much of it lies in fragmented sections. These corridors of land are often not large enough or have enough connections to support either the movement or day to day needs of many insect and animal species.



Some habitat is completely lost through physical alterations to the environment itself  — think bulldozing a thicket for a parking lot or strip mining for ore. Others are lost to what is called habitat degradation. Degradation happens when the quality of an environment is substantially changed or when one or more aspects of it become unsuitable for or incapable of supporting the native species who call it home.



Air pollution is a common cause of habitat degradation, triggering chemical changes in the vegetation on which insects feed. Studies show that insects feeding on the altered plants do not grow properly and thus do not return adequate nutrients to the soil when they die. Another form of pollution, light pollution, has been tied to declining numbers of night flying insects, especially fireflies.  



Invasive species are another way that habitats are altered. Invasive species enter into a habitat and compete with the native species for food. They tend to reproduce quickly which allows them to spread quickly. Many also tolerate a variety of conditions and have fewer natural predators than the native species. Invasive species can not only eliminate native species, they can become health hazards and cause billions of dollars in damage.

Climate Change



Recent studies have uncovered some unexpected and in some ways diametrically opposite correlations between climate change and insect populations and behavior.



Scientists at the University of Washington predict that climate change will result in higher rates of crop loss because insect activity will increase. Warmer temperatures ( 2 degrees C or 3.6 F) increase the metabolic rate of insects which boosts their appetites and increases their reproductive rates. In other words, there will be more pests eating higher amounts of food crops like corn, wheat and rice.



Other studies have shown that some species of insects are so sensitive to high temperatures that they will be unable to digest their meals or absorb the nutrients that they need to survive. Unable to ingest essential nutrients, they will either move to a more conducive environment or they will die out.




The loss of our insect populations is not to be taken lightly; it signals a potential for rapidly approaching catastrophic changes in our environment. But, like so many challenges in life, small changes can make huge differences. Join us next week as we examine a variety of steps, both simple and complex, that individuals and communities can take to  help rebuild our diminishing insect populations.