Birdwatching: DDT is long gone, but a new class of insecticide poses dangers

The International Union for Conservation of Nature listed the monarch butterfly as endangered in July. Gene J. Puskar/Associated Press

The general subject of this column came to me from two readings. An article in “Science” reports that 3 billion birds in North America have disappeared since 1970, a decrease of 30%. Virtually all types of birds have suffered these declines. Then there was the recent news that the monarch butterfly has been listed as an endangered species by the International Union for Conservation of Nature.

Of course, the question that immediately comes to mind is why? Why questions are fundamental to science. The scientific method is one of the most powerful ways humans have to know. But this methodology differs from arguments and inquiries in other areas of life.

Let’s start with a Major League Baseball player negotiating a new contract. His agent selectively reviews the player’s accomplishments, highlighting strengths and downplaying weaknesses. Meanwhile, the team’s general manager accentuates the player’s shortcomings and sells his achievements at a discount. Participants from both sides try to prove their particular point of view.

The selective use of information to construct an argument is found in many situations. Politicians on either side of the aisle pick the data in support of a position or bill. Family quarrels or arguments between friends are other examples.

However, the method of science is fundamentally different. A scientist makes observations, such as declining bird numbers, and then develops a hypothesis (essentially an educated guess) that might explain the pattern. Then the scientist collects data to try to refute the hypothesis.

If the information gathered does not refute the hypothesis, this explanation is tentatively considered true. Additional observations and experiments from different angles are carried out in an attempt to overturn this assumption.

It is only after multiple efforts to disprove a hypothesis that this explanation is credited. Even then, scientists realize that the jury is still out, and future experiments may well disprove the hypothesis.

So, scientists should be skeptical. The mode of scientific research is to refute hypotheses. Scientists accept a hypothesis as provisionally true, not because the scientist has proven it but because he has failed to disprove it. If you hear a scientist claiming that he has proven a hypothesis, he does not understand the scientific method.

The scientific method avoids the problem of a phenomenon called confirmation bias. A scientist may have a clever hypothesis to explain certain patterns in our world. But unconsciously, the scientist may downplay information that disproves the hypothesis and emphasize information that supports it. By trying to refute the hypothesis, this bias is eliminated. We can trust a hypothesis that has resisted multiple efforts to refute it.

Now back to the decline of birds and monarch butterflies. Following the US ban on DDT in 1972, chemists and agronomists sought to develop insecticides for crop protection without affecting other insects and animals. In 1999, a new class of insecticides called neonicotinoids was introduced.

Neonicotinoids (or neonicotinoids) are neuroactive insecticides, chemically similar to nicotine. The neonic named imidacloprid is today the most widely used insecticide in the world.

Neonics work well against sucking insects, some chewing insects and soil insects. In other words, agricultural pests. Early work showed that neonicotinoids have low toxicity in mammals.

Unfortunately, neonics affect other insects. Controlled experiments implicate neonicotinoids in colony collapse of bees and other pollinators. Bumblebee abundance has declined by 90% over the past 20 years. These insects are critical to most plants and virtually all crop plants. There is a certain irony here: neonics protect crops from herbivores but kill the pollinators that allow crop plants to produce.

The European Union has been more proactive in its response to pollinator decline caused by neonicotinoids. The three most common neonicotinoids were banned in Europe in 2018. Several US states followed suit.

An EPA statement released in August 2021 said that 80% of the 1,445 endangered species in the United States are negatively affected by neonics. This list includes plants, insects, birds, amphibians and freshwater invertebrates. These results are based on hundreds of scientific studies. What are we waiting for?

For an excellent review of the impacts of neonics on birds, see the recent article by Scott Weidensaul, one of our most gifted naturalist writers, in the Summer 2022 issue of “Living Bird” magazine.

Herb Wilson taught ornithology and other biology courses at Colby College. He welcomes comments and questions from readers to [email protected]

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