Why? Hypothesis: the milkweed may have been treated with pesticides before it was shipped to the nursery.
Newly published research led by scientists at the University of Nevada, Reno (UNR), in collaboration with the Xerces Society for Invertebrate Conservation--and appearing in the peer-reviewed science journal Biological Conservation--sheds some light on pesticide contamination of milkweed plants being sold in retail nurseries across the United States.
The article, titled "Milkweed Plants Bought at Nurseries May Expose Monarch Caterpillars to Harmful Pesticide Residues," indicates that every single plant tested in stores across the nation--every single one!--contained multiple pesticides, "even those that were labeled 'wildlife-friendly," according to the researchers, who included co-author Matt Forister, a UNR biology professor.
The team collected leaf samples from 235 milkweed plants purchased at 33 retail nurseries across the United States to screen for pesticides. "Across all samples, we detected 61 different pesticides with an average of 12.2 compounds per plant," they wrote in their abstract. "While only 9 of these compounds have been experimentally tested on monarch caterpillars, 38% of samples contained a pesticide above a concentration shown to have a sub-lethal effect for monarchs."
"In a previous study in California that primarily looked at milkweed in agriculture and urban interfaces, we had looked at a small number of plants from retail nurseries, and found that they contained pesticide but it was surprising to see the great diversity of pesticides found in these plants," Forister told Mike Wolterbeek in a Nevada Today news release. "In many ways, they are as contaminated or even worse than plants growing on the edges of agricultural fields. That was a surprise, at least to me."
Forister, who is the Trevor J. McMinn Endowed Professor in Biology, Foundation Professor, holds a doctorate in ecology from UC Davis, where he studied with major professor Art Shapiro, UC Davis distinguished professor of ecology and evolution.
Forister's doctoral student, Christopher Halsch, is the lead author of the paper. “The farther along in the life stage you go, the higher concentration you need to have a sublethal effect," Halsch explained. "For the caterpillars, this means a low concentration can have a more damaging effect than it would have on the butterflies.”
So did the plants labeled "wild-life friendly" have fewer pesticides on the leaves? No.
“That was the most shocking part," Halsch related. "The fact that plants labeled as potentially beneficial or at least friendly to wildlife are not better and in some cases might be worse than other plants available for purchase. This research sheds light on how pesticides may impact western monarchs, but many other butterflies are facing even steeper population declines, and pesticides are likely one driver.”
Thus, it's crucial that those milkweed plants that we purchase in retail stores--and elsewhere--be pollinator friendly and pesticide-free.
AsXerces' Pesticide Program Director Aimée Code, pointed out in the news article: “Everyone can take steps to address the risks we uncovered. Consumers can let their nurseries know they want plants that are free from harmful pesticides. Nursery outlets can talk with their suppliers and encourage safer practices, and government agencies can improve oversight. And it's important to keep gardening for pollinators for the long term, just take steps to reduce pesticide exposure: cover new plants the first year, water heavily, discard the soil before planting, as it may be contaminated, and avoid pesticide use.”
We asked entomologist and monarch researcher David James of Washington State University today what he thinks of the study: "We all suspected this was the case, given all the reports in social media of caterpillars dying, etc. I'm glad they did this scientific study to confirm it. Pretty shocking, really."
Indeed, scientists fear that the rapid decline of monarchs could lead to extinction. The International Union for the Conservation of Nature (IUCN) placed the migratory monarch butterfly on its Red List of threatened species on July 21, 2022, classifying it as endangered.
"In the 1990s, nearly 700 million monarchs made the epic flight each fall from the northern plains of the U.S. and Canada to sites in the oyamel fir forests north of Mexico City, and more than one million monarchs overwintered in forested groves on the California Coast," according to the Xerces Society. "Now, researchers and citizen scientists estimate that only a fraction of the population remains, monarchs have declined by more than 80% since the 1990s from central Mexico, and by more than 99% since the 1980s in coastal California."
So says Scott McArt, an assistant professor in the Cornell University's Department of Entomology, who will speak on "Pesticide Risk to Pollinators: What We Know and What We Need to Know Better" at the Wednesday, May 4 virtual seminar hosted by the UC Davis Department of Entomology and Nematology.
The seminar begins at 4:10 p.m. The Zoom link:
McArt, who joined the Cornell faculty in 2017, focuses his research on pollinator health and ecology. His areas of expertise include disease ecology, ecotoxicology, community ecology, chemical ecology, and plant-pollinator interactions. He maintains his lab research site at https://blogs.cornell.edu/mcartlab/.
"Research in our lab focuses on the impact of pesticides, pathogens, and habitat on honey bees and wild bees," he writes on his website. "We are particularly interested in scientific research that can inform management decisions by beekeepers, growers and the public. Current research projects include: 1) Understanding pesticide exposure and risk to bees in multiple land management contexts, 2) Combining empirical data with network modeling to understand pathogen transmission in complex plant-pollinator networks, and 3) Understanding how habitat enhancements (e.g., flowers at solar power sites) impact pollinator populations and the services they provide to agriculture."
McArt's duties at Cornell also include director of the Cornell Chemical Ecology Core Facility, and associate curator of the Cornell University Insect Collection.
He writes a monthly column, Notes from the Lab, in American Bee Journal; each month he summarizes scientific publications for a non-scientific audience. "The goal is to make the emerging pollinator health science more approachable and relevant to beekeepers," he says.
He is also a member of the New York State (NYS) Beekeeper Tech Team, which works directly with NYS beekeepers to improve honey bee health, reduce colony losses, and increase profitability of the state's beekeeping industry: https://pollinator.cals.cornell.edu/nys-beekeeper-tech-team/
In addition, McArt coordinates such beekeeping workshops as "Introduction to Honey Bee Queen Rearing" and "Honey Bee Biology and Disease Management for Veterinarians" and engages with growers regarding pesticide risk to bees and creating pollinator-friendly habitat. His extension materials are onsite.
When asked "What gets you out of bed in the morning?" during a new faculty interview, he responded "Most of the factors contributing to declines in bee health (pesticide exposure, lack of floral resources, disease, inadequate management practices) are preventable. With targeted research efforts and educated stakeholders, regulatory agencies and public, we can make a difference."
McArt holds a bachelor of arts degree in environmental and evolutionary biology (2001) from Dartmouth College, Hanover, N.H., and a master's degree in biological sciences (2006) from the University of Alaska, Anchorage. He received his doctorate in entomology in 2012 from Cornell University. He served as a USDA-NIFA (National Institute of Food and Agriculture) postdoctoral fellow at the University of Massachusetts, Amhurst, in 2014, and then as a research scientist at Cornell from 2014 to 2017, before joining the Cornell faculty.
Nematologist Shahid Siddique, assistant professor, UC Davis Department of Entomology and Nematology, is coordinating the spring seminars. For Zoom technical issues, contact him at email@example.com.
The honey bee guru continues to answer a range of questions. The latest concerns the effect of marijuana growing sites on honey bees.
We thought we'd share his answer, which deals with honey bees, pollinators, Cannabis, pesticides, and what could happen to beekeepers who stumble upon a pot farm.
The question: "What is the effect, good or bad, that marijuana plants and marijuana grow sites have on the honey bee? From what I understand, these grow sites are using chemicals to control pests year round. In some cases, I hear that marijuana growers are importing chemicals from Mexico that are stronger and work better to control pest."
Mussen answered the question succinctly and openly.
"As you might guess, since marijuana is still considered an illegal plant to grow by the federal government," he replied, "it is no surprise that there are no pesticides registered for use on the 'crop.' Some states are trying hard to build a list of acceptable products, but here is the problem. So far we have registered products based on contact and oral toxicities to mammals. We have only run inhalation toxicities on a few very potent and stinky products (fumigants). You can get up to 10X the dose of a chemical, from the same amount of plant mass, if you smoke it versus eating it.
"There are quite a number of websites dedicated to pot growing. When pest control becomes the topic, most sites suggest mechanical methods or use of products allowed in organic agriculture. However, those organic pesticides have not been checked for inhalation effects, either."
"Thus, practically any pesticide that is used will be illegal. Given that, growers are apt to determine which materials work best on the pest at hand on other crops, acquire those materials, and use them. The regulators know this, and in states where marijuana currently is legal, the states are testing some of the products on the shelves to see what pesticides are in them. The samples have been found to be pretty clean, for the most part."
Mussen acknowledged that blooming hemp plants are attractive to many pollinators. "I have no idea what the pollen and nectar might do to them when the bees consume it. We can provide a pretty good idea of what will happen when pesticide products used on other crops are applied to the bloom (at agricultural rates), but since nothing is registered, there is no way of guessing what might be used. For the standard fee of just under $400, we can send a sample of the bees or pollen to the USDA AMS pesticide residue detection lab in Gastonia, N.C., and they can tell us the residues. Butthat doesn't help us much in terms of regulatory assistance.
"Pot growers probably won't care if they repel or kill visiting bees," Mussen speculated. "Pollinated blossoms become senescent too quickly, and do not produce the maximum amount of important resins if they are pollinated early in their cycle."
"Up to this time, I have not heard of beekeepers reporting damage from pesticides applied to marijuana, but it is likely to happen before long. Beekeepers are more worried about being shot if they accidentally get too close to a pot farm."
Everyone from scientists to environmentalists to beekeepers are clamoring for more research on the effects of neonicotinoids on honey bees.
How do neonics affect queen bees?
Newly published research led by Geoffrey Williams of the Institute of Bee Health, Vetsuisse Faculty, University of Bern, Switzerland, indicates that neonics severely affect queen bees.
They published the article, Neonicotinoid Pesticides Severely Affect Honey Bee Queens, on Oct. 13 in the "Scientific Reports" section of Nature. The abstract:
"Queen health is crucial to colony survival of social bees. Recently, queen failure has been proposed to be a major driver of managed honey bee colony losses, yet few data exist concerning effects of environmental stressors on queens. Here we demonstrate for the first time that exposure to field-realistic concentrations of neonicotinoid pesticides during development can severely affect queens of western honey bees (Apis mellifera). In pesticide-exposed queens, reproductive anatomy (ovaries) and physiology (spermathecal-stored sperm quality and quantity), rather than flight behaviour, were compromised and likely corresponded to reduced queen success (alive and producing worker offspring). This study highlights the detriments of neonicotinoids to queens of environmentally and economically important social bees, and further strengthens the need for stringent risk assessments to safeguard biodiversity and ecosystem services that are vulnerable to these substances."
Williams and his research team correctly noted that "a plethora of literature has demonstrated lethal and sub-lethal effects of neonicotinoid pesticides on social bees in the field and laboratory" but that much of that research was done on worker bees.
"In this study, we hypothesised that exposure to field-realistic concentrations of neonicotinoid pesticides would significantly reduce honey bee queen performance due to possible changes in behaviour, and reproductive anatomy and physiology," they wrote. "To test this, we exposed developing honey bee queens to environmentally-relevant concentrations of the common neonicotinoid pesticides thiamethoxam and clothianidin. Both pesticides are widely applied in global agro-ecosystems and are accessible to pollinators such as social bees, but are currently subjected to two years of restricted use in the European Union because of concerns over their safety. Upon eclosion, queens were allowed to sexually mature. Flight behaviour was observed daily for 14 days, whereas production of worker offspring was observed weekly for 4 weeks. Surviving queens were sacrificed to examine their reproductive systems."
They called for more research on the effects of the pesticides on queen bee reproduction:
"Current regulatory requirements for evaluating safety of pesticides to bees fail to directly address effects on reproduction. This is troubling given the key importance of queens to colony survival and their frailty in adjusting to environmental conditions. Our findings highlight the apparent vulnerability of queen anatomy and physiology to common neonicotinoid pesticides, and demonstrate the need for future studies to identify appropriate measures of queen stress response, including vitellogenin expression. They additionally highlight the general lack of knowledge concerning both lethal and sub-lethal effects of these substances on queen bees, and the importance of proper evaluation of pesticide safety to insect reproduction, particularly for environmentally and economically important social bee species." Read the full report.
Meanwhile, the University of California, Davis, just held a sold-out conference on neonics. The speakers' presentations (slide shows) are posted on the California Center for Urban Horticulture's website.
Everyone agrees on this: more research is needed.
Based in the UC Davis Department of Entomology and Nematology, Mussen completed 38 years of service last June and is nationally and internationally known as "the honey bee guru."
"Most of us take pollinators for granted. That's a key reason why Gov. Jerry Brown has joined other governors throughout the country to celebrate June 15-21 as National Pollinator Week. It's a time to appreciate what bees, butterflies, beetles, bats and other pollinators do. Honey bees and native bees are especially important for the pollination of our agricultural crops. Without them, we'd be pretty much confined to a boring, unappealing and non-nutritious diet of wheat and rice."
"Many beekeepers can't keep their colonies alive, no thanks to pesticides, pests, parasites, diseases, stress and malnutrition. We humans negatively impact our bee populations by converting their natural habitat to an unnatural habit (for them): airports, highways, housing projects, shopping malls, and parking lots. Food sources and nesting habitat for pollinators continue to shrink. Use of herbicides reduces what little bee-food resources are left. In some cases, pesticides kill insect pollinators outright. In other cases, chronic exposure to sublethal doses of pesticide residues disrupts normal development of immature pollinators."
Mussen asks that we all "consider planting bee-attractive flowers that bloom well beyond late summer into fall. The colonies require good-sized populations of well-fed bees to survive through winter."
"Also, we should consider restricting the use of pesticides to those times that pollinators are not attracted to blooming flowers or weeds. This would prevent acute bee kills, contamination of stored pollens, and unnecessary use of bodily energy for detoxification of pesticide residues."
He adds: "It's good to see that the Almond Board of California--with the help of an advisory committee comprise of scientists, beekeepers and growers--generated a packet of materials: “Honey Bee Best Management Practices for California Almonds.” The impetus: a large number of colonies suffered serious pesticide damage during the 2014 almond pollination. The packets contain an 18-page pamphlet about honey bees, their management, and their protection. Included, as well, are two heavy-duty, laminated “Quick Guides” (in English and Spanish) to be taken into the fields as reminders of best management practices. You can request the free packets by contacting the Almond Board at (209) 549-8262 or downloading the document at http://www.almonds.com/growers/pollination. The information in the packets pertains equally well to most other crop situations."
"Our bees," Mussen says, "deserve the best."
That they do.