11
Sep
Continued Decline in Insect Species Biodiversity with Agricultural Pesticide Use Documented
(Beyond Pesticides, September 10, 2024) A literature review in Environments, written by researchers from South Korea and Ghana, highlights the threat to nontarget species and the biodiversity of insects that occur as a result of agricultural pesticide use. “Insects have experienced a greater species abundance decline than birds, plants, and other organisms, which could pose a significant challenge to global ecosystem management. Although other factors such as urbanisation, deforestation, monoculture, and industrialisation may have contributed to the decline in insect species, the extensive application of agro-chemicals appears to cause the most serious threat,†the authors state. The so-called “insect apocalypse†has been reported with one-quarter of the global insect population lost since 1990.Â
The authors, seeking to summarize the decline in insect species richness and abundance, link reliance on petrochemical pesticides and synthetic fertilizers to cascading negative impacts. Insects provide many important services, such as maintaining healthy soil, recycling nutrients, pollinating flowers and crops, and controlling pests. These nontarget and beneficial species are at risk through pesticide exposure, both directly and indirectly, which then affects these essential functions. Â
“Extensive and indiscriminate pesticide application on a commercial scale affects insect species abundance and non-target organisms by interfering with their growth, development, behaviour, and other metabolic and physiological processes,†the researchers find, based on their analysis of peer-reviewed scientific studies. The pesticide residues that contaminate plants and insects that provide a food source for other organisms can lead to population effects throughout multiple trophic levels. Since the active ingredients in pesticides can affect a wide range of taxonomic groups, they cause harm to numerous species rather than just the target species. Â
As the authors state, “Chemical residues pose a significant threat to species richness and abundance… For instance, the efficacy of [the weed killer] glyphosate requires plants to absorb its residues through their leaves or roots when applied. However, if glyphosate is accidentally spread on the ground, it is absorbed into soil particles and may remain active, threatening other species if not absorbed by the plant.†Whether nontarget insects are sprayed directly during pesticide application or are exposed to residues after spraying, this puts them at risk. Â
“Pesticides are known to be harmful to insects, with direct mortality frequently reported, with nontarget insects being the most vulnerable when compared to other insects,†the researchers comment. They continue, “These pesticides work directly by disrupting the insect’s nervous system or damaging its exoskeleton, causing paralysis and death.†With an increase in pesticide use, there is also an increase in related insect mortality.Â
As Dave Goulson, PhD says, an insect apocalypse is occurring that threatens all ecosystems. In an essay in Current Biology, he states, “Insects are integral to every terrestrial food web, being food for numerous birds, bats, reptiles, amphibians and fish, and performing vital roles such as pollination, pest control and nutrient recycling. Terrestrial and freshwater ecosystems will collapse without insects… we may have failed to appreciate the full scale and pace of environmental degradation caused by human activities in the Anthropocene.â€Â
The literature review authors reinforce this by saying, “The widespread use of pesticides in agricultural production has been identified as the primary cause of the overall loss of insect species and individual numbers†and studies show that insect declines appear to be much greater than those observed in birds or plants. “For instance, in 71% of butterfly species in Britain, the total number of individuals has decreased over 20 years, compared to birds (54% over 20 years), and plant species (28% over 20 years),†they note.Â
Direct pesticide exposure to insects causes changes within species and at the population level. The authors share examples: “Neonicotinoids increased bee and butterfly mortality while reducing their behaviour and survival. Glyphosate exposure caused changes in bees’ gut microbiome, leaving them vulnerable. In the United Kingdom, the direct effects of pesticides reduced butterfly species richness on conventional farms more than on organic farms.â€Â
Additional studies show the same concerning statistical trend for many pollinator species such as 45 butterfly species in Belgium, which declined by nearly 69%, and 733 moth species in the Netherlands, which declined by 85%, over the past century. 38% of these declining species are listed as threatened and 34% as susceptible by the European Red List of Threatened Species. (See original studies here and here.) Â
Effects of pesticides on species of bees are also heavily documented. “Agricultural intensification, chemical fertilisers, and pesticide application have been identified as the primary causes of bee species richness and abundance declines in Sweden. A comparable decline was observed in Europe (46% Bombus species), North America (50% of the 14 bumble bee species), Brazil (63%), Costa Rica (60%) and Finland (23%), China (3–13%), South Africa (29%), and Minnesota (11 stingless bees) as a result of extensive herbicide application,†the researchers state.Â
Varying effects on bee species are noted, as each species can have drastically different sensitivity to different chemicals. There are approximately 4,000 native bee species in the United States and hundreds of registered pesticides, each with the potential to negatively impact multiple species. “Historical records from 382 geographical areas in the United States show that 3.5 million out of 6.0 million honey bee populations have declined, representing a 0.9% loss per year,†the authors report, which they attribute to the use of pesticides on croplands. Â
Many other insects, such as Odonata (e.g., dragonflies), are also affected, which are important for pest control and mosquito management. “A previous study found that 118 aquatic insect species were threatened, with Odonata species accounting for 90%. A long-term comprehensive study found that 52 species of dragonflies and damselflies are declining in the United States, 15% of Odonata species are endangered, with two species of damselflies and dragonflies being highly vulnerable to extinction in Europe, and 57 Odonata species are declining in Japan,†the researchers specify. Â
Also of concern is the increased vulnerability to diseases, pathogens, and parasites that occur with exposure to pesticides. “Research shows that extensive and consistent application of insecticides stimulates the incidence of viral diseases and pathogens among insect pollinators. For instance, honey bees that fed on a neonicotinoid– and fipronil-treated field experienced higher pathogen infestation, reducing their population,†the authors say. An additional study, previously covered by Beyond Pesticides, shows that neonicotinoids can increase parasitism from Varroa mites in honey bees.  Â
The rapid decline in a myriad of insect species coincides with growing agricultural production demands due to a global increase in the human population. Estimates expect the population to reach over 9.7 billion by 2050, which only exacerbates the biodiversity crisis. According to the researchers, “The average pesticide usage worldwide is estimated to be 4.4 kg/ha per year, with agriculture accounting for roughly one-fifth of the Earth’s land area. As a result, insect diversity and other ecosystem services are severely threatened.â€Â
Pesticide usage in recent years has seen tremendous growth. “In 2022, the total pesticides used in agriculture was 3.70 million tonnes, representing a 4% increase from 2021, a 13% increase over a decade, and a doubling since 1990,†the authors note. These pesticides, such as malathion, methamidophos, abamectin, acetamiprid, imidacloprid, and acephate, are reported to be toxic to both target and nontarget insects, while other insecticides have been found to affect bugs (e.g., sucking insects), wild bees, and moth populations without impacting the actual target pests. Â
With large numbers of insects at risk, the reliance on pesticides in agriculture and land management threatens biodiversity. “Biodiversity is a key driver of ecosystem services… and thus it must be protected for current and future generations,†the authors state. Within this context, organic agriculture provides a holistic solution for enhancing and protecting biodiversity. Â
Managing land with organic methods provides multiple health and environmental benefits, and studies indicate “that it can increase species richness by approximately 34% and abundance by around 50%. Organic farming promotes biodiversity by increasing the abundance and variety of plant and insect species. This, in turn, can lead to enhanced biological control, as more predators can help regulate pest populations,†the researchers conclude. (See studies here and here.)Â
Promoting ecological balance and restoring biodiversity can be achieved through the elimination of petrochemical pesticides and synthetic fertilizers and with the adoption of organic practices. Studies show that organic farming has five times higher plant biodiversity and 20 times higher insect species richness compared to conventional farming and that higher biodiversity of insects is seen in fields with genetically diverse crops.Â
As previously reported by Beyond Pesticides, studies upon studies upon studies show that pesticides are a major contributor to the loss of insect biomass and diversity known as the “insect apocalypse,†particularly in combination with climate change. Insects are important as pollinators and as part of the food web that supports all life, so the loss of insects is a threat to life on Earth. Take action to protect biodiversity and keep organic strong with a focus on the health of all organisms.Â
Be part of the organic solution by becoming a member of Beyond Pesticides and stay informed with the Daily News Blog. Join the Parks for a Sustainable Future program as a Parks Advocate to transition your community to organic and make The Safer Choice to avoid hazardous home, garden, community, and food use pesticides.Â
All unattributed positions and opinions in this piece are those of Beyond Pesticides. Â
Source:Â
Quandahor, P. et al. (2024) Effects of agricultural pesticides on decline in insect species and individual numbers, Environments. Available at: https://www.mdpi.com/2076-3298/11/8/182.
