Brand: PHYTON ® MAGNUM ™ Insecticide Ear-Tag

Company: Y-TEX



  • zeta-cypermethrin: 10%
  • piperonyl butoxide: 20%
  • Tag weight: 15.4 g

CHEMICAL CLASS of the active ingredient(s):

INDICATIONS: CATTLE (beef & dairy)

PARASITES CONTROLLED* (spectrum of activity)



  • 1 tag per animal
  • All mature animals in the herd should be tagged.
  • Remove tags at end of fly season or prior to slaughter.


  • LD50 (acute oral) in rats: >1000 mg/kg (for the tag, according to MSDS)
  • LD50 (acute dermal) in rats: >5000 mg/kg (for the tag, according to MSDS)

Suspected poisoning? Read the article on cypermethrin safety in this site.


  • Meat: USA NIL.
  • Milk for human consumption: USA NIL.

2nd-generation synthetic pyrethroids (e.g. cyfluthrin, cyhalothrin, cypermethrin, deltamethrin, permethrin, etc.) are irritant to the eyes and the skin, both of humans and livestock. However, delivery through insecticidal ear-tags is usually less irritant than through pour-ons.



Risk of resistance? YES, resistance of horn flies (Haematobia irritans irritans) and houseflies (Musca domestica) to synthetic pyrethroids (incl. zeta-cypermethrin) is widespread worldwide, and can be very high, regardless of the delivery form (ear-tag, pour-on, spraying, dust bags, etc.). Cases of resistance to synthetic pyrethroids have also been reported for stable flies and little houseflies, but prevalence is usually low.

The synergist in the formulation (PBO) is supposed to neutralize resistance of parasites to synthetic pyrethroids. However, PBO works only against the so-called metabolic resistance (enhanced detoxification) caused by mixed function oxidases (= MFO), which is one among several mechanisms by which parasites can become resistant to synthetic pyrethroids and pesticides of other chemical classes. PBO specifically inhibits the activity of MFOs. If metabolic resistance is caused by other enzymes than MFOs, or if resistance is (also) due to other mechanisms such as target site insensitivity, reduced penetration or behavioral modifications, it won't be neutralized by PBO. In the vast majority of cases producers affected by parasites resistant to synthetic pyrethroids do not know which mechanisms make the parasites resistant, and it is mostly not possible to find it out. Consequently, whether the synergist PBO helps to overcome resistance or not is in fact a lottery.




It has been shown that horn flies resistant to synthetic pyrethroids are more susceptible to diazinon, an organophosphorous insecticide. This although resistance of horn flies to organophosphates has also been reported, but weaker than to synthetic pyrethroids. Since ear-tags with organophosphates are also available, a very reasonable strategy to prevent or at least delay resistance development is to rotate each year between these two chemical classes. Even better is to add a macrocyclic lactone (abamectin, doramectin, eprinomectin, ivermectin, moxidectin, etc.) into the rotation scheme, because the mechanism of action of these compounds is different from those of organophosphates and synthetic pyrethroids. Most macrocyclic lactones are available as pour-ons for the control of horn flies, a few ones also as ear-tags. Injectables and drenches do not control flies or other external parasites.

Learn more about resistance and how it develops.





COUNTRIES where this brand/product is marketed: USA

Click here to learn more about GENERIC vs. ORIGINAL drugs.

For an overview on the most used insecticidal EAR TAG brands click here.


PHYTON MAGNUM Insecticide Ear-tag for Cattle is one of the numerous insecticide-impregnated ear-tags for the control of flies & lice on cattle. Y-TEX markets also the PHYTON Insecticide Ear-tag, another tag with the same composition (10% zeta-cypermethrin + 20% piperonyl butoxide) but of lower weight than the PHYTON tag, i.e. it contains a smaller amount of active ingredients.

Zeta-cypermethrin is one of several standard isomer mixtures of cypermethrin (see below). Cypermethrin is one of several Type-II synthetic pyrethroids introduced by ICI & SHELL in the 1970s. Cypermethrin (all isomer mixtures together) is massively used worldwide in veterinary products as well as in agricultural and hygiene pesticides.





Control of susceptible (i.e. non-resistant) horn flies is usually excellent, because they spend a lot of time on cattle and thus are exposed to the insecticide for a long period of time. But as already mentioned, horn flies have developed high resistance to all synthetic pyrethroids in the USA and elsewhere. Biting lice are also exposed to topical insecticides for a long period of time because they never leave the host. In contrast with the behavior of horn flies, stable flies bite the treated animals anywhere in their bodies (often in the legs) and remain attached and thus exposed to the insecticide only during their blood meals that last a few seconds or minutes, which is often too short to kill them. Face flies remain on cattle only for short periods of time too. Trying to control housefly populations with on-animal topical products is usually ineffective. The simple reason is that they spend most of their time off-the animals.

All synthetic pyrethroids have a certain repellent effect, mainly on mosquitoes. The repellent effect on flies is weaker than on mosquitoes.

It is useful to know that the active ingredients of many synthetic pyrethroids consist in a mixture of various optical isomers, typically those called "cis", and those called "trans". Cypermethrin has 8 isomers, 4 cis and 4 trans. Manufacturers of active ingredients usually supply the raw material in standard qualities, for cypermethrin typically e.g. in a 40:60 or 80:20 cis:trans ratio. Zeta-cypermethrin is a mixture of 8 isomers with a 48:53 cis:trans ratio. It happens that the efficacy against parasites and the mammalian toxicity of these isomers are significantly different. Typically cis isomers are more effective insecticides but also more toxic to mammals. Obviously a cis:trans 80:20 mixture is more potent than a cis:trans 40:60 mixture. Qualities with higher cis content are usually also more expensive. And the higher the percentage of the most active isomer, the lower the rate that is required for achieving the same efficacy. 




In case of doubt contact the manufacturer or a veterinary professional.

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