Spinosad Explained

Spinosad is an insecticide based on chemical compounds found in the bacterial species Saccharopolyspora spinosa. The genus Saccharopolyspora was discovered in 1985 in isolates from crushed sugarcane. The bacteria produce yellowish-pink aerial hyphae, with bead-like chains of spores enclosed in a characteristic hairy sheath.[1] This genus is defined as aerobic, Gram-positive, nonacid-fast actinomycetes with fragmenting substrate mycelium. S. spinosa was isolated from soil collected inside a nonoperational sugar mill rum still in the Virgin Islands. Spinosad is a mixture of chemical compounds in the spinosyn family that has a generalized structure consisting of a unique tetracyclic ring system attached to an amino sugar (D-forosamine) and a neutral sugar (tri-Ο-methyl-L-rhamnose).[2] Spinosad is relatively nonpolar and not easily dissolved in water.[3]

Spinosad is a novel mode-of-action insecticide derived from a family of natural products obtained by fermentation of S. spinosa. Spinosyns occur in over 20 natural forms, and over 200 synthetic forms (spinosoids) have been produced in the lab.[4] Spinosad contains a mix of two spinosoids, spinosyn A, the major component, and spinosyn D (the minor component), in a roughly 17:3 ratio.

Mode of action

Spinosad is highly active, by both contact and ingestion, in numerous insect species.[5] Its overall protective effect varies with insect species and life stage. It affects certain species only in the adult stage, but can affect other species at more than one life stage. The species subject to very high rates of mortality as larvae, but not as adults, may gradually be controlled through sustained larval mortality. The mode of action of spinosoid insecticides is by a neural mechanism.[6] The spinosyns and spinosoids have a novel mode of action, primarily targeting binding sites on nicotinic acetylcholine receptors (nAChRs) of the insect nervous system that are distinct from those at which other insecticides have their activity. Spinosoid binding leads to disruption of acetylcholine neurotransmission. Spinosad also has secondary effects as a γ-amino-butyric acid (GABA) neurotransmitter agonist. It kills insects by hyperexcitation of the insect nervous system. Spinosad has proven not to cause cross-resistance to any other known insecticide.[7]

Uses

Spinosad has been used around the world for the control of a variety of insect pests, including Lepidoptera, Diptera, Thysanoptera, Coleoptera, Orthoptera, and Hymenoptera, and many others.[8] It was first registered as a pesticide in the United States for use on crops in 1997. Its labeled use rate is set at 1 ppm (1 mg a.i./kg of grain) and its maximum residue limit (MRL) or tolerance is set at 1.5 ppm. Spinosad's widespread commercial launch was deferred, awaiting final MRL or tolerance approvals in a few remaining grain-importing countries. It is considered a natural product, thus is approved for use in organic agriculture by numerous nations. Two other uses for spinosad are for pets and humans. Spinosad has been used in oral preparations (as Comfortis) to treat C. felis, the cat flea, in canines and felines; the optimal dose set for canines is reported to be 30 mg/kg.

Spinosad is sold under the brand names, Comfortis, Trifexis, and Natroba.[9] [10] Trifexis also includes milbemycin oxime. Comfortis and Trifexis brands treat adult fleas on pets; the latter also prevents heartworm disease.[11] Natroba is sold for treatment of human head lice.[12] Spinosad is also commonly used to kill thrips.[13]

Comfortis and Trifexis were withdrawn in the European Union.[14] [15]

Spinosyn A

Spinosyn A does not appear to interact directly with known insecticidal-relevant target sites, but rather acts via a novel mechanism. Spinosyn A resembles a GABA antagonist and is comparable to the effect of avermectin on insect neurons. Spinosyn A is highly active against neonate larvae of the tobacco budworm, Heliothis virescens, and is slightly more biologically active than . In general, spinosyns possessing a methyl group at C6 (spinosyn D-related analogs) tend to be more active and less affected by changes in the rest of the molecule. Spinosyn A is slow to penetrate to the internal fluids of larvae; it is also poorly metabolized once it enters the insect. The apparent lack of spinosyn A metabolism may contribute to its high level of activity, and may compensate for the slow rate of penetration.

Resistance

Spinosad resistance has been found in Musca domestica,[16] Plutella xylostella,[17] Bactrocera dorsalis,[18] Frankliniella occidentalis,[19] and Cydia pomonella.[20] [21] [22]

Safety and ecotoxicology

Spinosad has high efficacy, a broad insect pest spectrum, low mammalian toxicity, and a good environmental profile, a unique feature of the insecticide compared to others currently used for the protection of grain products. It is regarded as natural product-based, and approved for use in organic agriculture by numerous national and international certifications. Spinosad residues are highly stable on grains stored in bins, with protection ranging from 6 months to 2 years.Ecotoxicology parameters have been reported for spinosad, and are:[23]

Chronic exposure studies failed to induce tumor formation in rats and mice; mice given up to 51 mg/kg/day for 18 months resulted in no tumor formation.[24] Similarly, administration of 25 mg/kg/day to rats for 24 months did not result in tumor formation.[25]

Further reading

Notes and References

  1. Mertz F, Yao RC . Saccharopolyspora spinosa sp. nov. Isolated from soil Collected in a Sugar Mill Rum Still. International Journal of Systematic Bacteriology . Jan 1990 . 40. 1. 34–39. 10.1099/00207713-40-1-34. free.
  2. Snyder DE, Meyer J, Zimmermann AG, Qiao M, Gissendanner SJ, Cruthers LR, Slone RL, Young DR . 6 . Preliminary studies on the effectiveness of the novel pulicide, spinosad, for the treatment and control of fleas on dogs . Veterinary Parasitology . 150 . 4 . 345–351 . December 2007 . 17980490 . 10.1016/j.vetpar.2007.09.011 .
  3. Crouse GD, Sparks TC, Schoonover J, Gifford J, Dripps J, Bruce T, Larson LL, Garlich J, Hatton C, Hill RL, Worden TV, Martynow JG . 6 . Recent advances in the chemistry of spinosyns . Pest Management Science . 57 . 2 . 177–185 . February 2001 . 11455648 . 10.1002/1526-4998(200102)57:2<177::AID-PS281>3.0.CO;2-Z .
  4. Watson G . Actions of Insecticidal Spinosyns on γ-Aminobutyric Acid Responses for Small-Diameter Cockroach Neurons. Pesticide Biochemistry and Physiology. 31 May 2001. 71. 1 . 20–28. 10.1006/pest.2001.2559. 2001PBioP..71...20W .
  5. Hertlein M, Thompson GD, Subramanyam B, Athanassiou CG . Spinosad: A new natural product for stored grain protection. Stored Products. 12 January 2011. 47. 3. 131–146 . 10.1016/j.jspr.2011.01.004.
  6. Orr N, Shaffner AJ, Richey K, Crouse GD . Novel mode of action of spinosad: Receptor binding studies demonstrating lack of interaction with known insecticidal target sites. Pesticide Biochemistry and Physiology. 30 April 2009. 95. 1 . 1–5. 10.1016/j.pestbp.2009.04.009. 2009PBioP..95....1O .
  7. Sparks TC, Crouse GD, Durst G . Natural products as insecticides: the biology, biochemistry and quantitative structure-activity relationships of spinosyns and spinosoids . Pest Management Science . 57 . 10 . 896–905 . October 2001 . 11695182 . 10.1002/ps.358 .
  8. Sparks T, Dripps JE, Watson GB, Paroonagian D . Resistance and cross-resistance to the spinosyns- A review and analysis. Pesticide Biochemistry and Physiology. 102. 6 November 2012. 1 . 1–10. 17 November 2011. 10.1016/j.pestbp.2011.11.004. 2012PBioP.102....1S .
  9. Web site: Spinosad international brands . Drugs.com . 3 January 2020 . 30 January 2020.
  10. Web site: Spinosad US brands . Drugs.com . 3 January 2020 . 30 January 2020.
  11. Web site: Merchant M . Safer Flea Control | Insects in the City . Texas A&M AgriLife Extension Service . 20 October 2012.
  12. Web site: Spinosad - brand name list from . Drugs.com . 20 October 2012.
  13. Bethke JA, Dreistadt SH, Varela LG, Phillips PA, O'Donnell CA . Thripsm . University of California Statewide Integrated Pest Management Program. UCANR Publication. . May 2014 . Integrated Pest Management for Home Gardeners and Landscape Professionals .
  14. Web site: Comfortis EPAR . European Medicines Agency . 26 June 2023 . 3 July 2023.
  15. Web site: Trifexis EPAR . European Medicines Agency . 5 November 2020 . 3 July 2023.
  16. Liu N, Yue X . Insecticide resistance and cross-resistance in the house fly (Diptera: Muscidae) . Journal of Economic Entomology . 93 . 4 . 1269–1275 . August 2000 . 10985042 . 10.1603/0022-0493-93.4.1269 . 26611971 .
  17. Sayyed AH, Omar D, Wright DJ . Genetics of spinosad resistance in a multi-resistant field-selected population of Plutella xylostella . Pest Management Science . 60 . 8 . 827–832 . August 2004 . 15307676 . 10.1002/ps.869 .
  18. Hsu JC, Feng HT . Development of resistance to spinosad in oriental fruit fly (Diptera: Tephritidae) in laboratory selection and cross-resistance . Journal of Economic Entomology . 99 . 3 . 931–936 . June 2006 . 16813333 . 10.1603/0022-0493-99.3.931 . 182038998 .
  19. Bielza P, Quinto V, Fernandez E, Grávalos C, Contreras J . Genetics of spinosad resistance in Frankliniella occidentalis (Thysanoptera: Thripidae) . Journal of Economic Entomology . 100 . 3 . 916–920 . June 2007 . 17598556 . 10.1603/0022-0493(2007)100[916:gosrif]2.0.co;2 . 25560262 .
  20. Reyes M, Franck P, Charmillot PJ, Ioriatti C, Olivares J, Pasqualini E, Sauphanor B . Diversity of insecticide resistance mechanisms and spectrum in European populations of the codling moth, Cydia pomonella . Pest Management Science . 63 . 9 . 890–902 . September 2007 . 17665366 . 10.1002/ps.1421 .
  21. See for continued updates: Web site: Mota-Sanchez D, Wise JC . . Arthropod Pesticide Resistance Database . Michigan State University .
  22. Biondi A, Mommaerts V, Smagghe G, Viñuela E, Zappalà L, Desneux N . The non-target impact of spinosyns on beneficial arthropods . Pest Management Science . 68 . 12 . 1523–1536 . December 2012 . 23109262 . 10.1002/ps.3396 . Society of Chemical Industry (Wiley) .
  23. Web site: Brunner JF . Codling Moth and Leafroller Control Using Chemicals . Tree Fruit Research and Extension Center . Washington State University . https://web.archive.org/web/20030803114827/http://entomology.tfrec.wsu.edu/jfbhome/growerarticles/newchems/newchems.pdf . 3 August 2003 . 20 October 2012.
  24. Stebbins KE, Bond DM, Novilla MN, Reasor MJ . Spinosad insecticide: subchronic and chronic toxicity and lack of carcinogenicity in CD-1 mice . Toxicological Sciences . 65 . 2 . 276–287 . February 2002 . 11812932 . 10.1093/toxsci/65.2.276 . free .
  25. Yano BL, Bond DM, Novilla MN, McFadden LG, Reasor MJ . Spinosad insecticide: subchronic and chronic toxicity and lack of carcinogenicity in Fischer 344 rats . Toxicological Sciences . 65 . 2 . 288–298 . February 2002 . 11812933 . 10.1093/toxsci/65.2.288 . free .

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