Neonicotinoids: Neonicotinoid insecticides also pose a threat to mammals

Neonicotinoids—insecticides used on croplands—are already a major contributor to the insect decline. New studies show that they can also harm vertebrates, both large and small.   Chemically similar to nicotine, neonicotinoids were developed in the 1990s to combat insects that ravage crops. Marketed as a safer and more sustainable alternative to toxic agricultural chemicals, they are now the most widely used pesticides in the world. They are effective against aphids and leafhoppers, as well as a wide range of worms, beetles, and borers. The product coats the seeds of crops grown on more than 150 million hectares in the United States. As the plant grows, it absorbs and incorporates the insecticide, making its roots, stems, leaves, fruits, pollen, and nectar toxic to insects that feed on them. It is therefore no surprise that neonicotinoids are having an impact on pollinator populations in Europe and North America. Bees, which are essential for crop pollination, are particularly affected. The European Union has responded by banning the outdoor use of three common forms of this insecticide, but this is not enough, especially in light of new findings. In fact, the product does not affect only plants and insects. In recent years, scientists have found that only 5% of the neonicotinoid coating on seeds is absorbed by plants. The rest accumulates in the environment, in soil and waterways. Wild animals, which are also exposed to the insecticide, are thus subjected to its harmful effects. Even large mammals are not spared. In 2015, a team of scientists from the University of South Dakota demonstrated that imidacloprid—a neonicotinoid used on corn, soybeans, wheat, and cotton—accumulates in the spleens of deer. When mixed with the water they drink, the insecticide appears to cause these large herbivores to have smaller jaws, reduced body weight, and underdeveloped organs, including reproductive organs. Over the two-year study period, more than one-third of the fawns died prematurely, with imidacloprid levels in their spleens significantly higher than in the others. In particular, researchers noted that fawns and adults exposed to high concentrations of the insecticide are less active, making them more vulnerable to predators. And unfortunately, this happens more often than one might imagine. Furthermore, in North Dakota, some wild deer are exposed to the insecticide at levels three times higher than those that posed a problem in the 2015 study. Published in *Scientific Reports* in 2019, these findings are cause for concern. Animals exposed to the insecticide that develop malformed jaws and undersized reproductive organs may have difficulty feeding or reproducing, leading to catastrophic consequences for populations.     These findings are disputed by Bayer CropScience, formerly Monsanto, one of the world’s largest manufacturers of neonicotinoids and the leading supplier of imidacloprid. According to its spokesperson, Alexander Hennig, one of the reasons neonicotinoids were developed as insecticides is precisely because they do not affect vertebrates, as they bind to cellular receptors that are much less prevalent in these species. In fact, their use has been approved to protect pets and livestock against fleas and ticks. However, these negative effects are not limited to deer. In total, 15 to 30 percent of river otter and lynx populations in North Dakota are also believed to be contaminated. Canadian researchers have shown that consuming just four canola seeds treated with imidacloprid over three days impairs a sparrow’s ability to migrate. Other researchers in Canada have found that ring-necked pheasants become thinner, weaker, and more lethargic as they consume treated corn kernels. They also lay fewer eggs, build their nests later, and experience a 20% higher chick mortality rate. These results can be replicated in the laboratory. In rats, exposure to neonicotinoids reduces sperm production and increases miscarriages and skeletal abnormalities. The insecticides also suppress the immune response in mice, impair sexual function in lizards, alter the mobility of tadpoles, increase miscarriages and premature births in rabbits, and reduce the survival of red-legged partridges, both adults and chicks. But these animals are not the only ones exposed. Humans, who consume produce from treated crops, come into direct contact with neonicotinoids. In a 2015 study conducted by the American Bird Conservancy and the Harvard T.H. Chan School of Public Health, neonicotinoid residues were found—albeit at levels deemed acceptable by the Environmental Protection Agency (EPA)—in nearly every meal served in the cafeterias of U.S. Capitol buildings. Another 2019 study by the National Institutes of Health detected traces of neonicotinoids in 49.1% of human urine samples. Over the past decade, the EPA has recorded more than 1,600 cases of human poisoning from imidacloprid. However, to date, there is still no direct evidence of adverse public health effects from dietary exposure to neonicotinoids. Clearly, further research on the impact of neonicotinoids on vertebrates is needed. But field studies on animals are rare, as they require a great deal of time, effort, and money. Few U.S. states fund such research, as Minnesota and South Dakota have done. Empirical data are difficult to collect, and poisoned and/or malformed wild animals often die before they can be studied. Yet these studies are of paramount importance for biodiversity and the health of ecosystems, animals, and humans.