A look back at the time when the entire world thought bt corn was killing monarchs

September 2, 2020


Hello everyone,


I'd like to start by thanking the readers and followers for taking the time to read this blog. I realized this summer that by now I have been doing this for 5 years, and there are now over 100 blog entries! So if you are reading this, then I hope you have found this website useful. It was always my hope that this site would serve as a useful forum for the dissemination of science around this bug that we all know and love. And, that it teaches people to do something that I think we all need to do more of these days - to think critically about what we "think" we know.


Today's topic is exactly the kind of piece that will make you do that. 


This year marks the 20th anniversary, more or less, of the time when the entire world went bonkers over a single study about monarchs. I've spent the last couple of days perusing the archives of the internet to refresh my memory of that time, and I can tell you that it is utterly fascinating. This story has lots of characters, including scientists, media, industry, and the public, and there are twists and turns. To be honest, I'm not sure if I can dispel it all in a single blog post.


Let me set the stage for you. It's the late 90s, and the world is just coming to grips with the invention of genetically-modified foods. These are crops (and now animals) where scientists have modified the plant DNA to improve the crop in some way. These modifications could be for improving the shelf-life of apples, or making the fruits of a plant bigger, or making rice plants more drought-tolerant, etc. One of these modified crops was corn (and I think soy), which had been modified to contain its own pesticide, so to speak. The bacteria, Bacillus thuringiensis (Bt) makes proteins that can kill insects, and scientists spliced genes from that bacteria into corn, so that the corn now makes the protein! This is quite clever actually. In theory this was designed to help the farmers, so that they need not spray pesticides over the crops - they could just let the corn plants do that for them!


I think it's fair to say that the world was not ready for these new foods back then, and maybe some people still aren't. There was, and still is, considerable resistance to the idea of genetic modification, where people felt like scientists were tinkering dangerously with nature, and making "frankenstein foods" that were going to either kill us, or run amok in the environment. I certainly know this gut feeling, but I also know that so far, these modifications appear to be working, and there have been no human health issues from these foods after 20+ years of us eating them.


Around this same time of intense public debate over these foods, a group of researchers from Cornell were working on a project that examined the impact of Bt corn on monarch caterpillars. John Losey, Linda Rayor and Maureen Carter had been examining what happens when monarch caterpillars consume pollen from these transgenic corn crops. They reasoned that since crop fields often contain milkweeds, that some of the corn pollen can get blown onto milkweed leaves, and then consumed by monarch larvae. So, they conducted an experiment in their lab where they fed caterpillars milkweed that was "dusted" with pollen from several varieties of transgenic corn. A lot of the caterpillars died. So, like any scientists would do, they next worked to get their paper published in a scientific journal. 


They initially submitted their findings to the journal, Science, one of the premiere scientific journals in the world. It was rejected on the grounds that the findings were too preliminary and there were some serious drawbacks to the methods they used (I'll talk about these later). The authors next submitted it to the journal, Nature, which is also highly prestigious. Nature decided that the article would be acceptable for their section on "preliminary findings", and it was published in May 1999. Here is the link to the original article - https://www.nature.com/articles/20338. The title of the study speaks for itself - "Transgenic pollen harms monarch larvae".


What followed next was a world-wide media frenzy the likes of which these poor scientists had never before experienced. The press went crazy, and here are a couple of archived articles, from the New York Times, and CNN. And here is one from a conservation group called the Environmental Defense Fund, which is still around today - https://www.edf.org/news/genetic-engineering-kills-monarch-butterflies. The title of the EDF article speaks volumes - "Genetic Engineering Kills Monarch Butterflies". I don't know if all of this frenzy was spurred by the public resistance to GMO crops, but I strongly suspect it to be so. I do know that the Environmental Defense Fund is a group that is strongly opposed to big agro-business. I see that they jumped on this one study and ran with it. Incidentally, I took a screenshot of the EDF article below:



I note that from the wording of this piece, and from the comments from the expert, it sounds like the evidence here is pretty solid right?


In addition to this media frenzy, it sounds like this paper was the talk of a lot of scientific conferences and on email chat boards among scientists. There were a lot of eyes on it, and everyone was checking and re-checking their procedures. To be fair, I'm not sure if this level of scrutiny was deserved, because this will only ever end in one way.


Sure enough, there were problems found with the experiment, and these problems were well-documented in a number of followup studies, essays and commentaries by other scientists. I'll put a couple links here. This one is from a very distinguished researcher, May Berenbaum, who wrote a very detailed summary of the problems, and of the hoopla surrounding this paper - link here.  This one is from Dr. Mark Sears, from the University of Guelph, who led a two-year study of the effects of Bt corn to monarchs.


I can try to summarize the issues that were found. First, the Cornell researchers did not really quantify how much pollen dust they used in their lab. They really did seem to just "sprinkle" it onto the milkweeds, in a very unscientific way. Thus, they did not really know if this is the true amount of pollen that a monarch would ingest if it were in a cornfield. And, it seems that upon followup testing, the dosages that they used were indeed wrong, since they did not mimic what is ingested by larvae in the field. Also, they had a control group in their lab, which were monarchs that ate non-modified corn pollen, but it turns out this variety of corn was not the same as the one in the other groups. Another issue, was the way in which they "harvested" corn pollen for their experiment. They obtained it by shaking corn stalks into a bin (or a container of some sort). This not only dislodges the pollen, but also bits of corn husks and dust, etc., which is harmful in itself to caterpillars. And finally, the biggest blow was the fact that they only examined a couple of transgenic corn varieties, and the one variety that they did use, happened to be the one that is least planted (less than 2% of crops at the time), and, this percentage was even declining. So all in all, most scientists who read this paper appeared to agree that it did not stand up to scrutiny.


In the months and year that followed, there were a series of followup up studies that appeared to drive the final nails into the coffin of that study. In one study, Dr. Berenbaum and colleagues conducted a followup study of the effect of Bt corn pollen on swallowtail caterpillars AND monarch caterpillars, in which they found no ill effect. Here is a New York Times article describing this new evidence. There was the research led by Sears that I mentioned earlier, and I note that Drs. Oberhauser and Pleasants were also coauthors of the study (linked here). In fact, there were 6 published studies that came out together in 2001 (link here) which each provided bits of additional evidence that all added up to one conclusion - Bt corn is not killing monarchs, and the original study was wrong.


Let me step back from this story a bit here and ask what you might be wondering too - how did the science go wrong here, and how did the public-side of the story go so wrong too?


Let me start with the first part - was the science wrong? As an objective observer, I would have to say no. In my opinion this lab-based study was not really wrong, since they did seem to come to a conclusion - they found that if you sprinkle pollen from a very toxic transgenic corn plant onto milkweed leaves, any monarch caterpillar that eats it will die. This part seems like a reasonable interpretation of their results. Where the researchers WERE at fault, was in trying to extrapolate these preliminary results from a small lab study to what would happen in the field, and then to what would ultimately happen to the entire monarch population. After all, their study WAS published in a "preliminary findings" section of the journal. And, the authors then went on a media blitz then telling people that their results "clearly" show that bt corn is killing monarchs.


Guess who else was wrong here - the media. Don't get me wrong, I'm not a right-wing, anti-media, fake-news, anything. But in that case 20 years ago, it does seem like everyone, including some scientists, jumped to a very very fast conclusion and was very quick to run with it. And then, as they say in the news business, that story had legs. Once it got out, it went viral (or as viral as could be in that early internet age). If you think about it, it was such a juicy story, really, since it pitted the big, bad agribusinesses against the lowly and charismatic butterfly, and, at a time when the world was looking for a reason to be against GMOs. 


As a scientist, I'm bothered by the fact that the science in that case appeared to be misrepresented to the point where the public perception did not match what the study actually showed. I guess one of the reasons I've been thinking about this lately is because of the state of things today with monarchs, and public perception of them. Right now, everyone seems to just "know" that monarchs are declining and that it is because of roundup-ready crops that reduced the milkweeds in farm fields. All of the media articles are saying this these days, and a lot of scientists are saying this.


We were all wrong before. Are we again?


By the way, just last week I got a letter from the Environmental Defense Fund. It had monarch butterflies on the envelope and it said that we must act now (donate to them) before it is too late, because monarchs are on the verge of extinction, since big agriculture has wiped out their milkweeds.


Ponder away, folks. That's all for now.



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The science of monarch butterflies

A blog about monarchs, written by a monarch scientist, for people who love monarchs