A Monsanto larvicide isn’t causing microcephaly in Brazil (or anywhere else)

The alarming number of babies with microcephaly in Brazil and other countries is definitely a cause for concern. While each day more and more evidence grows that it is related to infection with the Zika virus, definitive studies are still lacking. This sadly leaves room for conspiracy theories and the one currently making the rounds is that a larvicide (a pesticide to kill mosquito larvae) called pyriproxyfen is causing the microcephaly. I’ve seen posts about the supposed link shared several times this weekend on Facebook and several news sites have irresponsibly elevated this to almost truth status.



Guess what I found when I clicked the links from the medical group making these claims? The same group that made the outrageous and incorrect claims about tampons being Monsanto-fueled vaginal cancer sticks.

The idea that pyriproxyfen could cause these birth defects is not biologically sound. First of all, pyriproxyfen works by interfering with the hormonal regulation of insect hatching from larvae, a cycle obviously absent in humans.

Secondly, it has been well studied and is poorly absorbed from the gastrointestinal tract/ The minute amount that is absorbed is rapidly excreted (eliminated). Scimex interviewed real toxicologists who study these chemicals and how they prevent mosquito borne diseases and if you want to know more it is an informative and concise read. Here is the best quote from Professor Andrew Batholomaeus, a consultant toxicologist from the School of Pharmacy, University of Canberra and the Therapeutic Research Unit, School of Medicine, University of Queensland:

Studies in rats and rabbits have shown pyriproxyfen to have no reproductive or developmental effects at doses up to at least 100 mg per kg of body-weight every day. This intake would be equivalent to an average human female consuming 6 grams of the compound per day. The acceptable daily intake of pyriproxyfen set by the WHO is 100 micrograms per kg of body-weight per day for a lifetime.

This equates to approximately 6 mg per person per day. By contrast the WHO recommended addition of pyriproxyfen to drinking water storage is a maximum of 10 micrograms per litre which would deliver a daily dose of 20 micrograms. A microgram is one millionth of a gram. Thus, the intake of pyriproxifen in Brazil from treated drinking water is of the order of 300 times lower than the safe limit set by the WHO.
All of this information is readily available to any genuine scientist looking dispassionately at the potential causes of the Zika virus outbreak or the rise in malformations in Brazil. Also readily available is the knowledge that the use of pyriproxifen is driven by WHO recommendations and not the marketing activity of any multinational or other corporation.

This last bit is VERY important, this kind of fear mongering could reduce the use of larvicides – the very thing that can help reduce the problem. Apparently the Brazilian State of Rio Grande Do Sul has suspended use of the larvicide.

The claims from the “Physicians in the Crop Sprayed Town” is either A) an attention grab to promote another agenda or B) a gross misunderstanding of biology. Any news site that promotes this link as worth “looking into” is contributing to the harm of those who live in areas rife with mosquito born illnesses.


A great follower on Twitter pointed out that Monsanto doesn’t even make the pesticide in question

Join the Conversation


  1. Actually there is evidence that juvenile hormone analogs do have an effect in mammals, specifically in developing embryos. In fact they have been show to act on the retinoid receptor system which is a known pathway causing microcephaly in infants. Very small doses in the first weeks of pregnancy can disrupt embryo development. This is the same mechanism by which retinol is known to cause birth defects, including… Wait for it… Microcephaly!

    You really haven’t done your homework. I suggest that you should start by looking into the effect of methoprene, another juvenile hormone analogs, on RXR receptors in mammals, and maybe take it from there.
    The Brazilian doctors who first raised this issue are on the money. The coincidence of timing and distribution of pyriproxyfen being added to drinking water supplies and the emergence of microcephaly is remarkable. Combined with the demonstrated ability of JH analogs to exert an influence on the RxR receptors of mammals, specifically embryos, and the well established association with retinol and microcephaly…. They have a very strong case. Zika on the other hand, not so much.

    You really need to take a second look at this and do some actual research. I think you’ll be shocked at the clear evidence that JH does exert an effect on developmental pathways in mammalian embryos. The evidence is unequivocal

    1. At doses of 100 mg/kg/day there is no evidence of malformations. That would work out to drinking about 1,000 liters of water a day to get that dose. At doses over 300 mg/kg/day (so the equivalent of a woman eating a tablespoon raw of the larvicide a day during pregnancy) there were some visceral malformations and pelvic. I find no evidence of microcephaly in the studies I reviewed.

      There’s no coincidence at all. The chemical has been in use since the 1990s. The spray it directly on citrus in several countries, yet no one in Israel or South Africa has been harmed by it So, it’s you who haven’t done your research. But it’s always easy to hide behind anonymity and and absence of scientific articles!

  2. colombia register 2824 Pregnant with zika and no cases of microcephaly.
    zika is fraud and false flag. 4000 cases of microcephaly this number reduced to 270 zika suspects and only 8 confirmed with zika with microcefaliar
    cases of zika is in northeastern Brazil concentrates 86% of cases and not in the whole Brazil. There decades in Africa and has no reporting microcefaliar in Africa. It is a globalist agenda for vaccines death by government and famarceuticos laboratories. In the same year he released transgenic mosquitoes had dengue epidemic in sao paulo in 2014

    Brazil has 205 million people on average have less 300 cases. US has on average 25,000 per year, but is not news, because there is alliance of governments worldwide in support of an agenda.
    “Workers Party” PT “and feminist movement has interest to legalize abortion in Brazil general ……. they will get in the coming months in the Supreme Court with federal safety mandate to legalize abortion by the supreme because in Congress national does not pass. but today dilma president can not even go out on the street who is booed their popularity is the Brazil’s history the worst. since President Dilma won in 2014 with less 2% of the candidate’s difference aecio nevess opposition.
     The President of Brazil Dilma wants to use combat the mosquito that transmits dengue and zika etc …. to distract the people, because your government is in the news involved in several corruption scandals involving members of his party and allies arrested for corruption and the process impeachment in the coming months. use mosquito fight to distract the people, but many Brazilians have already agreed to it.

    1 website

    site 2 http://www.bbc.com/portuguese/noticias/2016/02/160201_zika_aborto_temporao_rs

    site 3

    of Rio Grande do Sul The government suspended on Saturday (13) the use of water for human consumption pyriproxyfen larvicide used to stop the development of the mosquito larvae Aedes aegypti, the transmitter zika virus. The product is manufactured by Sumitomo Chemical.

    public ministry wants to know about transgenic mosquitoes Oxitec British company.

    Olympic Games is in the winter and the mosquitoes do not play. further proof that the carnival usually followed in Brazil

    1. This is all conspiracy theory and little facts.

      Zika is real, whether it causes microcephaly is not yet known but the virus has been ideentified in miscarried fetuses, in an aborted fetus at 32 weeks with severe microcephaly, and in a microcephalic baby born this year in Hawaii to a mother who was in Brazil. Also, there was a spike in these kinds of birth defects in Tahiti after the 2013 outbreak there.

  3. I saw this meme on another blog, and I appreciate your thorough investigation. I will disseminate as I can.

  4. I wish the articles would STOP calling it a “Monsanto” larvicide/insecticide, etc. It was NOT made by Monsanto. It was made by a Japanese company – Sumitomo. Calling it a, “Monsanto larvicide” only fuels the anti-Science, fear-mongering loons.

  5. Yeah-I figured it was BS-but STILL-why did Microcephaly suddenly become an issue when the virus has been out there for Decades?? And why aren’t there many cases in neighboring countries such as Columbia?? I’m hearing that Zika-negative women and babies are getting microcephaly??

    1. The virus hasn’t been an issue for decades, there have only been sporadic cases from 1952-2007. The outbreak in 2007 was 50 or so cases. The massive spike in infections was 2015.

      Given many affected countries have limited resources it will take some time to truly figure everything out. There may be a similar uptick in microcephaly everywhere with the virus, Brazil may have more disease (may have worse overcrowding or a standing water problem), or there may be a mutation that has made local mosquitoes resistant to the spraying effort.

  6. The only OBVIOUS question is modality of intake. The good doctor speaks of ingestion, into the stomach. A spray would be via skin, eyes, etc. absorption. No safe levels for that have been provided nor addressed. As a complex systems safety engineer we still have hazard modalities to cross off the list. But thanks for the article. I live in Mexico, am way past the breeding age but am wondering about my granddaughters. If a child gets the virus now will it affect their own children later in life? It is the questions not asked that gotcha. Regards, Richard the Mr. Murphy proponent.

    1. Actually this is an incredibly well studies pesticide. It is sprayed on citrus in many countries and dissipates rapidly from the soil and water table. We use it in California for fire ants.

      There is no adverse effects in animal studies up to 100 mg/kg/day of ingestion throughout gestation.

  7. Dr. Jen Gunter is …. she speaks on everything from autism to agricultural sciences apparently now. Shiva Ayyadurai has a PhD from MIT & has studied this particular issue well. I think I would trust his opinion on this over a SF gyno….

    1. Hey Doug, I took out the insult. Next time you leave one you get flagged for spam.

      I only let the rest of your post in to correct you as Dr.Ayyadurai has no published research on larvicides and birth defects or the toxicology of larvicides that I can find. If it is not your field it doesn’t really matter where you studied. However, if you have a peer reviewed source then post it.

      However, the data is available to anyone who can Google so don’t take the word of a simple GYN, read the papers yourself.

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