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Chemical structure of pyriproxyfen
IUPAC names
4-Phenoxyphenyl (R/S)-2-(2-pyridyloxy)propyl ether
3D model (JSmol)
ECHA InfoCard 100.102.814 Edit this at Wikidata
  • InChI=1S/C20H19NO3/c1-16(23-20-9-5-6-14-21-20)15-22-17-10-12-19(13-11-17)24-18-7-3-2-4-8-18/h2-14,16H,15H2,1H3 checkY
  • InChI=1/C20H19NO3/c1-16(23-20-9-5-6-14-21-20)15-22-17-10-12-19(13-11-17)24-18-7-3-2-4-8-18/h2-14,16H,15H2,1H3
  • O(c1ncccc1)C(COc3ccc(Oc2ccccc2)cc3)C
Molar mass 321.376 g·mol−1
Appearance Colorless crystals[1]
Density 1.2 g/cm3[1]
Melting point 48–50 °C (118–122 °F; 321–323 K)[2]
Boiling point 318 °C (604 °F; 591 K)[2]
0.367 mg/L[2]
QP53AX23 (WHO)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
☒N verify (what is checkY☒N ?)
Infobox references

Pyriproxyfen is a pesticide which is found to be effective against a variety of insects.[3] It was introduced to the US in 1996, to protect cotton crops against whitefly. It has also been found useful for protecting other crops.[4] It is also used as a prevention for flea control on household pets, for killing indoor and outdoor ants and roaches.[5] Methods of application include aerosols, bait, carpet powders, foggers, shampoos and pet collars.[6]

Pyriproxyfen is a juvenile hormone analog and an insect growth regulator.[7] It prevents larvae from developing into adulthood and thus rendering them unable to reproduce.[8]

In the US, pyriproxyfen is often marketed under the trade name Nylar.[9] In Europe, pyriproxyfen is known under the brand names Cyclio (Virbac)[10] and Exil Flea Free TwinSpot (Emax).

Toxicity in mammals[edit]

Pyriproxyfen has low acute toxicity.[11] According to WHO and FAO, at elevated doses exceeding 5000 mg/kg of body weight, pyriproxyfen affects the liver in mice, rats and dogs.[12] It also changes cholesterol levels, and may cause modest anemia at high doses.[13]

Rumor of link to microcephaly outbreak in Brazil[edit]

Starting in 2014, pyriproxifen was put into Brazilian water supplies to fight the proliferation of mosquito larvae.[14] This is in line with the World Health Organization (WHO)'s Pesticide Evaluation Scheme (WHOPES) for larvicides.[15] In January 2016, the Brazilian Association for Collective Health (Abrasco; Portuguese: Associação Brasileira de Saúde Coletiva) criticized the introduction of pyriproxyfen in Brazil. Abrasco demanded the "immediate suspension of [use of] pyriproxyfen and all growth inhibitors ... in drinking water." The organization is opposed to the use of growth inhibitors in the context of an ongoing outbreak of fetal malformation.[16]

On February 3, the rumor that pyriproxyfen, not the Zika virus, is the cause of the 2015-2016 microcephaly outbreak in Brazil was raised in a report of the Argentinean organization Physicians in the Crop-Sprayed Villages (PCST).[17] It attracted wide media coverage.[18][19] The statement from Abrasco was cited in the PCST report; subsequently, Abrasco clarified that position as an misinterpretation of their statement, saying "at no time did we state that pesticides, insecticides, or other chemicals are responsible for the increasing number of microcephaly cases in Brazil". They also condemned the behavior of the websites that spread the misinformation, adding that such "untruths...violates the anguish and suffering of the people in vulnerable positions".[20] In addition, the coordinator for the PCST statement, Medardo Ávila Vazquez, acknowledged in an interview that "the group hasn’t done any lab studies or epidemiological research to support its assertions, but it argues that using larvicides may cause human deformities."[21]

On February 13, the Brazilian state of Rio Grande do Sul suspended pyriproxyfen's use, citing both Abrasco and PCST positions.[22][23] The Health Minister of Brazil, Marcelo Castro, criticized this step, noting that the claim is "a rumor lacking logic and sense. It has no basis." They also noted that the insecticide is approved by the National Sanitary Monitoring Agency and "all regulatory agencies in the whole world". The manufacturer of the insecticide, Sumitomo Chemical, stated "there is no scientific basis for such a claim" and also referred to the approval of pyriproxyfen by the World Health Organization since 2004 and the United States Environmental Protection Agency since 2001.[24][25]

George Dimech, the director of Disease Control and Diseases of the Health Department of Pernambuco in Brazil, gave an interview to the BBC where he pointed out that the city of Recife has the current highest reported number of cases of microcephaly, yet pyriproxyfen is not used in the region, but another insecticide altogether. He added that "this lack of spatial correlation weakens the idea that the larvicide is the cause of the problem." In addition, the BBC interviewed researchers in Pernambuco, where no evidence has been found of the cases being linked to any environmental cause like an insecticide. Neurologist Vanessa van der Linden stated in an interview, "Clinically, the changes we see in the scans of babies suggest that the injuries were caused by congenital infection and not by larvicide, drug or vaccine."[20]

Noted skeptic David Gorski called the claim a conspiracy theory and pointed out that antivaccine proponents had also claimed that the Tdap vaccine was the cause of the microcephaly outbreak, due to its introduction in 2014, along with adding, "One can’t help but wonder what else the Brazilian Ministry of Health did in 2014 that cranks can blame microcephaly on." Gorski also pointed out the extensive physiochemical understanding of pyriproxyfen coded in the WHO Guidelines for Drinking-water Quality, which concluded in a past evaluation that the insecticide is not genotoxic, and that the doctor organization making the claim has been advocating against all pesticides since 2010, complicating their reliability.[26][27][28]

A professor from the University of Adelaide in Australia, stated that "The effect of pyriproxyfen on reproduction and fetal abnormalities is well studied in animals. In a variety of animal species even enormous quantities of pyriproxyfen do not cause the defects seen during the recent Zika outbreak."[29] A colleague also from the University of Adelaide stated that "While the evidence that Zika virus is responsible for the rise in microcephaly in Brazil is not conclusive, the role of pyriproxyfen is simply not plausible."[29] Another professor in Australia concluded that "insect development is quite different to human development and involves different hormones, developmental pathways and sets of genes, so it cannot be assumed that chemicals affecting insect development also influence mammalian development."[29]

See also[edit]


  1. ^ a b "Pyriproxifen". National Institute for Occupational Safety and Health.
  2. ^ a b c "WHO Specifications and Evaluations for Public Health Pesticides: Pyriproxifen" (PDF).
  3. ^ Ishaaya, I; Horowitz, AR (1995). "Pyriproxyfen, a Novel Insect Growth Regulator for Controlling Whiteflies : Mechanisms and Resistance Management". Pestic. Sci. 43 (3): 227–232. doi:10.1002/ps.2780430308.
  4. ^ Devillers, James (May 6, 2013). Juvenile Hormones and Juvenoids: Modeling Biological Effects and Environmental Fate. CRC Press. pp. 108–126. ISBN 9781466513228.
  5. ^ Maddison, Jill E.; Page, Stephen W.; Church, David (2008). Small Animal Clinical Pharmacology. Elsevier Health Sciences. p. 226. ISBN 9780702028588.
  6. ^ "Federal Register | Pyriproxyfen; Pesticide Tolerances". Retrieved 2016-02-28.
  7. ^ "PyriproxyfenGeneral Fact Sheet". National Pesticide Information Center, Oregon State University Extension Services.
  8. ^ Szabo, Liz (February 16, 2016). "Scientists debunk theory linking pesticide, not Zika, to birth defects". USA Today. Retrieved February 16, 2016.
  9. ^ Goss, G. Robert (1997). Pesticide Formulations and Application Systems. ASTM International. pp. 87–93. ISBN 9780803124691.
  10. ^ Rock, Amanda; Bowden, Sally; Cousquer, Glen (2007). Veterinary Pharmacology: A Practical Guide for the Veterinary Nurse. Elsevier Health Sciences. p. 96. ISBN 9780750688628.
  11. ^ "Toxicological evaluations". Retrieved 2016-04-13. was not necessary to establish an acute reference dose because of the low acute toxicity of pyriproxyfen.
  12. ^ "Toxicological evaluations". Retrieved 2016-02-28.
  13. ^ "Pyriproxyfen in Drinking-water, Background document for development of WHO Guidelines for Drinking-water Quality" (PDF).
  14. ^ "Technical instructions for the utilization of the larvicide pyriproxyfen (0.5 G) for the control of Aedes aegypti", Brazilian Ministry of Health
  15. ^ WHOPES-recommended compounds and formulations for control of mosquito larvae (25 October 2013)
  16. ^ "Nota técnica sobre microcefalia e doenças vetoriais relacionadas ao Aedes aegypti: os perigos das abordagens com larvicidas e nebulizações químicas – fumacê" [Technical note on microcephaly and vector diseases related to the Aedes aegypti: the dangers of approaches using larvicides and chemical nebulization] (in Portuguese). Brazilian Association for Collective Health (Associação Brasileira de Saúde Coletiva, Abrasco). reivindicamos das autoridades competentes a adoção das medidas a seguir: ... (3) Nas medidas adotadas pelo MS [Ministério da Saúde] para controle de Aedes aegypti em suas formas larva e adulto, imediata suspensão do Pyriproxyfen (0,5 G) e de todos os inibidores de crescimento como o Diflubenzuron e o Novaluron, ou qualquer outro produto químico ou biológico em água potável.
  17. ^ "Report from Physicians in the Crop-Sprayed Villages regarding Dengue-Zika, microcephaly, and mass-spraying with chemical poisons", Coordinator: Dr. Medardo Avila Vazquez: “Malformations detected in thousands of children from pregnant women living in areas where the Brazilian state added pyriproxyfen to drinking water is not a coincidence, even though the Ministry of Health places a direct blame on Zika virus for this damage, while trying to ignore its responsibility and ruling out the hypothesis of direct and cumulative chemical damage caused by years of endocrine and immunological disruption of the affected population.,” PCST said.
  18. ^ "Argentine and Brazilian doctors suspect mosquito insecticide as cause of microcephaly". Ecologist.
  19. ^ Almendrala, Anna (February 16, 2016). "A Viral Story Links The Zika Crisis To Monsanto. Don't Believe It". Huffington Post. Retrieved February 16, 2016.
  20. ^ a b Entidade diz ter sido mal-interpretada e não ver ligação entre microcefalia e larvicida
  21. ^ Johnson, Reed; Jelmayer, Rogerio (February 15, 2016). "Brazil State Bans Pesticide After Zika Claim". Wall Street Journal. Retrieved February 16, 2016.
  22. ^ Zika virus: Brazil dismisses link between larvicide and microcephaly
  23. ^ Rio Grande do Sul discontinues the use of larvicide Pyriproxyfen against Aedes aegypti mosquitoes (RS suspende uso de larvicida Pyriproxyfen no combate ao mosquito Aedes)
  24. ^ "Brazilian state suspends larvicide used to combat Zika virus". Fox News Latino. February 14, 2016.
  25. ^ "Report says Monsanto-linked pesticide is to blame for microcephaly outbreak - not Zika". Science Alert. 16 February 2016. Retrieved 2016-02-16.
  26. ^ Gorski, David (February 15, 2016). "Oh, myyyy! George Takei falls for a Zika virus conspiracy theory". Respectful Insolence. ScienceBlogs. Retrieved February 15, 2016.
  27. ^ "Chemical hazards in drinking-water: Pyriproxyfen". World Health Organization. Retrieved 15 February 2016.
  28. ^ EFSA (European Food Safety Authority), 2014. Conclusion on the peer review of the pesticide risk assessment of confirmatory data submitted for the active substance pyriproxyfen. EFSA Journal 2014;12(8):3813, 19 pp. doi:10.2903/j.efsa.2014.3813 PDF Aces. Jan. 13
  29. ^ a b c "EXPERT REACTION: Is a pesticide, not Zika virus, causing microcephaly?". SCIMEX. 15 February 2016. Retrieved 2016-02-16.

External links[edit]