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  • Andy Davis

New report from the National Academy of Science involving the GMO - monarch story

Greetings all,

Yesterday, a report was released that is of interest to those that follow monarchs - pertaining to the issue of GMO crops and their effects on humans and the environment, including monarch butterflies. This blog entry will focus on that report.

First, let me set the stage for this report. for those of my readers who aren't scientists (good for you, by the way, for taking the time to read my blog), I should point out who wrote this report. The National Academy is the 'big leagues' of science. This is a group of the world's leading scientists, and to get into this group is a major (career-topping?) achievement for us scientists. I don't think I'll ever get there, but I suspect my wife will... This group also publishes one of the top three scientific journals in the world - "The Proceedings of the National Academy of Sciences", and getting a research paper published in that journal is also a major achievement for a scientist. Anyway, this group also serves as a kind of scientific advisor on all things of human importance. If that's not clear enough, I'll cut and paste a description of them directly from their main website:

"The National Academy of Sciences (NAS) is a private, non-profit society of distinguished scholars. Established by an Act of Congress, signed by President Abraham Lincoln in 1863, the NAS is charged with providing independent, objective advice to the nation on matters related to science and technology. Scientists are elected by their peers to membership in the NAS for outstanding contributions to research. The NAS is committed to furthering science in America, and its members are active contributors to the international scientific community. Nearly 500 members of the NAS have won Nobel Prizes, and the Proceedings of the National Academy of Sciences, founded in 1914, is today one of the premier international journals publishing the results of original research."

So it looks like this group was given the task of sorting out the deal with GMO crops, that is, are they safe? That led them to look through all of the scientific research on the subject, and then they drew some conclusions based on the research. In this sense then, this report is almost like an independent 'review' of the relevant research. In the end, they concluded that GMOs are mostly safe to eat, which was the primary focus of the report. However, there was an interesting part in the report about the monarch issue. Apparently, they were well-aware of the fact that GMO crops have led to a reduction in milkweeds in agricultural fields, because farmers can now spray herbicide on their 'herbicide-resistant' crops during the summer and get rid of all non-crop plants (like milkweeds). See the image below of milkweed plants in a cornfield. This fact has then led to the notion that the decline of monarchs in Mexico is the result of this loss of milkweeds. So the group set out to review the evidence for this link between GMO crops and monarch declines.

The photo above shows milkweed plants within a cornfield - I grabbed this from John Pleasants' website (he's an expert on this subject).

Instead of telling you what they said I'm going to directly cut and paste the relevant section pertaining to monarchs here. Remember, this is a review of the evidence, from independent scientists.

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NOTE FROM ANDY - there was an initial paragraph here about the Bt-corn issue from the early 2000s, but I'll skip that and jump to the main part.

"In addition to the potential for a direct effect of Bt maize on monarch butterfly populations, it is possible that HR (NOTE FROM ANDY - THIS MEANS "HERBICIDE RESISTANT") crops indirectly affected monarch populations if they resulted in reducing the abundance of milkweed plants, which are the sole food source for monarch caterpillars. Hartzler (2010) documented a 90-percent decline in the area within Iowa agricultural fields occupied by milkweed from 1999 through 2009 that was due primarily to the use of glyphosate. Pleasants and Oberhauser (2013) used those data and other data on abundance of milkweed in non-crop areas of Iowa to estimate the overall decline in milkweed. They estimated that milkweed abundance declined by 58 percent from 1999 to 2010; but on the basis of data showing more eggs laid on milkweed plants within crops, there was an estimated 81- percent decline in potential production of monarchs in Iowa. Data at that level of detail are not available for other areas of the monarch range. (Of course, decline in milkweed are likely to have been beneficial to some farmers but the specific impacts of milkweed on maize and soybean profitability are not available.)

There are data that demonstrated a decline in the density of monarchs at overwintering sites in Mexico. The average total hectares occupied by dense aggregations of adults during the winters of 1995–2002 was about 9.3, but the average for 2003–2011 was 5.5 with a general trend of decline (Brower et al., 2012). The decline has continued to below 0.7 hectares in 2014, but it was expected to increase in 2015 to 3–4 hectares (Yucatan Times, 2015).

The cause–effect relationship between lower abundance of milkweed in the United States and decreasing overwintering populations is uncertain. If lower abundance of milkweed is limiting the monarch populations, there is expected to be an indication of it in their population dynamics beyond winter habitats in Mexico. A series of articles published in 2015 examined data from researchers and citizen scientists collected in 1995–2014 on dynamics of monarch populations as they moved north in spring and began moving south in fall (Steffy, 2015; Badgett and Davis, 2015; Crewe and McCracken, 2015; Howard and Davis, 2015, Nail et al., 2015; Ries et al., 2015; Stenoien et al., 2015). There was year-to-year variation in the population sizes but little evidence of decline of the monarchs during that period.

A general conclusion from the work was that “while the overwintering population (and early spring migration) appears to be shrinking in size, these early monarchs appear to be compensating with a high reproductive output, which allows the subsequent generations of monarchs to fully recolonize their breeding range in eastern North America” (Howard and Davis, 2015:669). The researchers recommended more detailed studies to understand what causes the fall decline. That recommendation was echoed in a paper by Inamine et al. (2016) (NOTE FROM ANDY - I DISCUSSED THAT PAPER IN THE PREVIOUS BLOG ENTRY) that also could find no evidence that lower abundance of milkweed resulted in monarch decline. The authors hypothesized that such factors as low nectar abundance and habitat fragmentation could be affecting survival during fall migration.

Pleasants et al. (2016) critiqued the conclusion of no evidence of a decline drawn by Howard and Davis (2015), and Pleasants et al. has been rebutted in turn by Dyer and Forister (2016). Without detailed data, it is difficult to exclude the possibility that declines in the overwintering populations were caused by extreme weather events, or parasites and pathogens. Resolving this debate will require modeling and direct experimental assessment of the extent to which milkweed abundance affects monarch population size. A long-term study providing a complete life-cycle analysis of the monarch butterfly is called for."

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So I have to give credit to this group for taking the time to read all of those papers, and for pretty much getting the story straight. As they pointed out, there is conflicting evidence for the loss of agricultural-based milkweeds being the 'cause' of the monarch declines in Mexico. And, there is right now an ongoing debate among the monarch scientists about the various datasets we have, which ones are more important, and the various ways of interpreting them. In short, it's complicated, and things are still unfolding. Until then, it would be wrong for anyone (including scientists, reporters, or laypeople) to make sweeping claims that they have the answer regarding population trends of eastern North American monarch butterflies.

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

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