Study fails to let GM crops off the hook for monarch butterfly decline

Experts criticise pro-GMO study as unreliable and divorced from reality

Glyphosate-tolerant GM crops have come in for a bashing from researchers and the public alike over their effect on the catastrophic decline in monarch butterflies. The problem is that milkweed, the only food of the monarch larvae, is wiped out by the glyphosate herbicides applied to GM glyphosate-tolerant crops. Scientists have cited the spread of these GM crops as a major factor in the decline of monarchs, whose numbers have decreased by over 80% between 1999 and 2016. Around 850 million milkweed plants — representing 71% of the monarchs’ food — have vanished from corn and soybean fields in the past 20 years, according to Iowa State University researcher Dr John Pleasants.



Facts like this have led the Non-GMO Project in the US, which provides non-GMO certification to food companies, to use the iconic orange butterfly in its logo. The fact that the logo works in the marketplace is testament to the public relations problem suffered by GM glyphosate-tolerant crops.



Given this context, the GMO lobby has publicly rejoiced at the appearance of a new paper authored by J.H. Boyle and colleagues at the University of California, Los Angeles and published in PNAS (a pre-press free copy is available here; the abstract is below this article). The new paper shifts much of the blame for the monarch's decline away from GM crops and onto other factors. The paper's title lays out its pitch: "Monarch butterfly and milkweed declines substantially predate the use of genetically modified crops". The authors used museum collections of monarch butterflies to conclude that monarch numbers began falling in the 1950s, decades before GM glyphosate-tolerant crops were introduced. Therefore, they conclude, "laying the blame so heavily on GM crops" is not "well supported by data": "Herbicide-resistant crops... are clearly not the only culprit and, likely, not even the primary culprit."



The paper has been much hyped by GMO promoters such as the Genetic Literacy Project. In India, the Deccan Herald subtitled its article, "New findings give body blow to anti-GM campaign".

Bafflement

At GMWatch, we were baffled. We couldn't understand how the authors accurately calculated the numbers of monarchs in the years prior to 1993, when systematic monitoring of monarchs began. How could museum specimens give quantitative information – in simple terms, how could they give an accurate picture of the numbers of monarchs present in any particular area? Those of us who know collectors recognize that their choice of which particular items to gather and store can be highly idiosyncratic. In the case of living organisms like butterflies, surely the numbers collected of any one species would be biased by factors such as the collector's individual preferences and collection methods?



We are not entomologists, however, so we waited for the experts to weigh in – and they obliged. One of the first was Tyson Wepprich, an entomologist at Oregon State University. Wepprich laid out his thoughts on Twitter and in an article on the pre-press website BioRxiv. He pointed out that Boyle and colleagues had tried to control for inconsistencies that might arise from collection practices by assessing monarch abundance as a proportion of all museum specimens of Lepidoptera (the class of organisms that contains butterflies and moths). But Wepprich says they missed the fact that Lepidoptera collection methods changed over the last century in a way that favours the collection of moths.



In the 1940s, Lepidoptera collectors began using light traps to collect specimens. These are especially good at capturing nocturnal moths. According to Wepprich, this change in collection methods was responsible for a proportional rise in moths in museum collections, beginning in the 1950s. To correct for this, Wepprich reassessed the new study data for monarch abundance as a proportion of butterflies only – and found that the trend in monarch records showed no mid-century decline and in fact that they increased over recent decades. However, this trend in museum specimens contradicts the recent trend in monarch abundance documented from systematic population monitoring – in other words, the catastrophic decline that such monitoring suggests occurred in tandem with the spread of GM glyphosate-tolerant crops.



Wepprich concluded that such museum records are "unreliable for abundance estimates. The conclusion in Boyle et al... that monarch declines started in the mid-20th century is unwarranted both because the trend is biased by sampling changes in museum records and because the trend in monarch records, when corrected, does not correspond with real-world population abundance."



Wepprich has also submitted a letter containing his findings to PNAS.



He says his interventions changed the tone of the online conversation: It went “from people reading [the PNAS paper’s] headline and assuming glyphosate is absolved of responsibility, to people looking more critically at insect abundance claims from spotty records".

"We can't go back in time" to monitor monarch numbers

Other scientists have also been critical of Boyle and colleagues' paper. In a balanced piece for Scientific American subtitled, "Some scientists question museum data analysis that suggests Roundup is not responsible for the insects’ decline", Manu Saunders, an ecologist at the University of New England in Australia, is quoted as saying, “To really know what’s happening with them [the monarchs], we need to have been monitoring them for a long time. Of course, that hasn’t happened, and we can’t go back in time to do that now.”



Elise Zipkin, an ecologist at Michigan State University, told Scientific American, “We have no indication of where people surveyed, how much they surveyed, or where they didn’t survey." Zipkin added that records only show whether or not a specimen was present in a museum’s collection. Leslie Ries, an ecologist at Georgetown University, agreed. “It’s really difficult to use museum records to look at abundance trends,” she said, explaining that many collections do not necessarily reflect what happened in the real world. “A lot of them come from collections where somebody did a lot of collecting in a certain area during a certain time” and ecological models have to carefully account for that process, she said.



Boyle and colleagues' publication – whatever the intention of the authors – appears to fit squarely into the long tradition of papers that "manufacture doubt" about the environmental problems caused by risky technologies.



That it should have met with such a prompt backlash by experts may be testament to the declining ability of the GMO lobby to pull the wool over the eyes of the scientific community with regard to the plight of the monarch butterfly.

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The new study details:



Monarch butterfly and milkweed declines substantially predate the use of genetically modified crops

J. H. Boyle, H. J. Dalgleish, and J. R. Puzey

PNAS February 19, 2019 116 (8) 3006-3011; published ahead of print February 19, 2019 https://doi.org/10.1073/pnas.1811437116

https://www.pnas.org/content/116/8/3006



Significance



The recent decline of the monarch butterfly has attracted a great deal of attention. One of the leading hypotheses blames genetically modified (GM) crops, ostensibly because of the impact of GM-related herbicide use on the monarch’s food plants, milkweeds. Here, we use museum specimen records to chart monarch and milkweed occurrence over the past century (1900 to 2016), dating well before previous datasets begin (in 1993). We show that monarch and milkweed declines begin around 1950 and continue until the present day. Whatever factors caused milkweed and monarch declines prior to the introduction of GM crops may still be at play, and, hence, laying the blame so heavily on GM crops is neither parsimonious nor well supported by data.



Abstract



Monarch butterfly (Danaus plexippus) decline over the past 25 years has received considerable public and scientific attention, in large part because its decline, and that of its milkweed (Asclepias spp.) host plant, have been linked to genetically modified (GM) crops and associated herbicide use. Here, we use museum and herbaria specimens to extend our knowledge of the dynamics of both monarchs and milkweeds in the United States to more than a century, from 1900 to 2016. We show that both monarchs and milkweeds increased during the early 20th century and that recent declines are actually part of a much longer-term decline in both monarchs and milkweed beginning around 1950. Herbicide-resistant crops, therefore, are clearly not the only culprit and, likely, not even the primary culprit: Not only did monarch and milkweed declines begin decades before GM crops were introduced, but other variables, particularly a decline in the number of farms, predict common milkweed trends more strongly over the period studied here.