Effects of neonicitinoid insecticides on Western monarchs

Dr. David G. James of Washington State University gave a presentation on the effects of widespread use of neonicitinoid insecticides (neonics) on monarch butterflies and other invertebrate species at the 2020 Western Monarch Summit, held January 10 – 12, 2020.  Neonics are currently the most widely used pesticides in the world.  Neonics were developed in the 1980s and 1990s as a replacement for organophosphate pesticides, which were banned in the US in 2001 for residential use but are still permitted for agricultural use and in public spaces such as parks.  Neonics are less toxic to birds and mammals than insects.  Today, neonics are the primary ingredients used in agriculture and home pesticide products.  

In recent years neonic use has been associated with declines in honeybee and other pollinator insect populations.  Toxicity of neonics to bees is probably due to a variety of “sub-lethal” effects, such as reduced ovary development, reduced reproductive success, impaired foraging, and impaired predator avoidance, rather than acute lethal effects.  There have been relatively few studies of neonic effects on butterfly populations.  

Is it possible that widespread use of neonics is one factor contributing to the decline in the Western monarch population?  Numerous studies have documented the spread of neonics in the environment.  Neonics are relatively stable in ground water and spread readily from the original site of application.  They are now present in surface and ground water throughout California.  Neonics are taken up by plants and are present in nectar, including the nectar of milkweed that is critical for the life cycle of Western monarchs!  Levels of neonics are found not only in agricultural crops but at even higher levels in home gardens, landscaping plants, and greenhouse crops.  They are present throughout the food chain and their effects on humans have not been thoroughly studied.  

Dr. James presented the results of his recently published study on the effects of neonics on monarch butterflies.  In a carefully controlled study Dr. James showed that monarchs fed nectar laced with neonics resulted in shortened longevity, to as few as 8 days, as compared with monarchs fed unadulterated nectar that survived as long as 22 days or longer.  Although more studies are needed, Dr. James’ research shows that neonics are very likely to be an important factor in the decline of the monarch population.  

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