Bee-killing neonicotinoids also lower crop yields by poisoning slugs predators

(NaturalNews) The world's most widely used pesticides - already implicated in worldwide declines in pollinator populations - may actually reduce crop yields by wiping out native predators of agricultural pests, suggests a study conducted by researchers from Penn State and the University of South Florida and published in the Journal of Applied Ecology.

The research focused on slugs, which are not insects and are not killed by the pesticides.

"Slugs are among the most challenging pests faced by Mid-Atlantic no-till growers," said researcher John Tooker. "Our research reveals that neonicotinoids can indirectly increase slug damage to crops by poisoning insects that eat slugs. As a result, crop yields are lower."

Pesticides actually lower crop yield

Neonicotinoids (also sometimes referred to as "neonics") were originally promoted as a safer alternative to older pesticides, because they can be used in smaller concentrations. Neonics are systemic insecticides, which are applied to seeds and then taken up into every tissue of the plant. This makes a neonic-treated plant poisonous for its entire life.

Scientists raised concerns about the potential ecological consequences of such pesticides from the start; in recent years, evidence has increasingly emerged that such concern was well founded.

In the new study, researchers exposed slugs to soybeans that were either treated with the common neonic thiamethoxam, treated with a fungicide, or not chemically treated at all. They then measured the weight and survival rates of the three groups over time. The surviving slugs were then fed to a species of ground beetle that naturally preys on them, and the beetles were observed for mortality and for symptoms of poisoning.

"In our lab work, we found that slugs were unaffected by the fungicides and also unaffected by the neonicotinoid insecticides, likely because they are mollusks and not insects," Tooker said. "But the slugs did transmit the insecticide to the ground beetles, impairing or killing more than 60 percent of the beetles."

The researchers then seeded quarter-acre plots with either untreated soybeans or with neonic-treated soybeans. They monitored the establishment and growth of the crops, populations of slugs and slug predators, and evidence of predation on slugs.

Samples collected in both the laboratory and field portions of the research were sent to a lab to test for levels of neonicotinoids. Samples included slugs, beetles, soybean plants and soil.

The field study found that neonic-treated fields had lower populations of insect predators and high populations of slugs. The pesticide-treated fields actually had a 19 percent lower crop density and a 5 percent lower yield than the untreated fields.

"Our research suggests that neonicotinoids can have unintended costs, even within crop production," Tooker said.

The study was also one of the first to confirm that insect predators do indeed regulate slug populations.

"This phenomenon dispels the common belief in the United States that insect predators do not contribute to slug control," Tooker said. "It also emphasizes that if growers care for these predator populations they can help with slug control."

As bad as DDT

The study is only the latest in a growing body of research that has led for calls for neonicotinoid use to be banned or drastically scaled back.

"Neonicotinoids are the most widely used insecticides in the world," researcher Margaret Douglas said. "Seed applications of neonicotinoids are often viewed as cheap insurance against pest problems, but our results suggest that they can sometimes worsen pest problems and should be used with care."

A recent review of more than 800 scientific studies concluded that neonicotinoids pose threats to wildlife and ecosystems on par with the threat once posed by DDT. Neonic-treated plants have been shown to poison not just pollinators and insect pests, but also birds, fish and important soil invertebrates.

(Natural News Science)

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