Company: ELANCO

DELIVERY FORM: «feed additives and medicated feeds» for oral administration.

ACTIVE INGREDIENT(S): cyromazine 10 g/kg (equivalent to 1.0%)

CHEMICAL CLASS of the active ingredient(s): insect growth regulators


PARASITES CONTROLLED (spectrum of activity)


  • Mix 1 lb of Larvadex 1% Premix per ton of feed.
  • Feed the treated feed as a daily ration.
  • Begin feeding when adult flies become active and continue treatment as prescribed through the fly season.
  • Feed Larvadex 1% Premix continuously as directed for 4 to 6 weeks. Usually, this is enough time for Larvadex 1% Premix to thoroughly cover the droppings and break the fly population cycle in the poultry house.
  • After a minimum of 4 to 6 weeks of Larvadex 1% Premix feeding, carefully examine the manure pits. If little or no activity is observed in the manure, discontinue Larvadex 1% Premix and continue the sanitary and management program. Continue monitoring the manure pits. If maggots become active again, repeat the procedure.

Read the product label for specific detail on dosage.

* Country-specific differences may apply: read the product label.


  • LD50 (acute oral) in rats: 3387 mg/kg (for the a.i.)
  • LD50 (acute dermal) in rats: >3100 mg/kg (for the a.i.)

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

Withholding periods (=withdrawal times) in days for meat & milk (country-specific differences may apply: read the product label)

  • Meat: 3 days (72 hrs.); Do not feed Larvadex 1% Premix treated feed to broiler poultry. Larvadex 1% Premix use in poultry is limited to use as a feed-through in chicken layer and breeder operations only and may not be fed to any other poultry species.

WARNING !!!: Never use on humans, dogs or cats

You may be interested in the following articles in this site dealing with the general safety of veterinary products:


Risk of resistance? YES

There are numerous reports on tolerant or even resistant houseflies to cyromazine in many countries (USA, UK, Denmark, Argentina, Brazil, etc.). This is not surprising more than 40 years after its introduction in the early 1980s. However, in most cases resistance factors are rather low (<10) and can be considered as tolerance or reduced susceptibility rather than resistance. Nevertheless, when administered as a feed-through larvicide, such low resistance factors can be enough to reduced efficacy, because the concentration of cyromazine achieved in poultry manure is quite close to the minimum efficient concentration (MEC) against housefly larvae. This is due to the fact that higher feed-through concentrations of cyromazine would leave excessive residues in meat and eggs.

This means that if this product does not achieve the expected efficacy against the mentioned parasites, there is a real risk that it is due to resistance and not to incorrect use, which is usually the most frequent cause of product failure.

Alternative chemical classes/active ingredients to prevent resistance of houseflies through product rotation:

These alternative products may not be available in all countries or may not be effective against all the concerned parasites.

To prevent or at least delay resistance, it is highly recommended to alternate feed-through cyromazine with fly adulticides used off animal (e.g. baits, paint-ons, premise sprays) in poultry premises. Such adulticides contain mainly neonicotinoids (e.g. imidacloprid, thiamethoxam), phenylpyrazoles (e.g. fipronil), organophosphates, carbamates (e.g. methomyl), or synthetic pyrethroids. However, housefly resistance to such adulticides is also quite frequent in many countries, particularly to organophosphates, carbamates, or synthetic pyrethroids.

Learn more about resistance and how it develops.


Are the active ingredients of this product ORIGINAL* or GENERICS**?


*Meaning that they are still patent protected and generics are not yet available
**Meaning that they have lost patent protection and may be acquired from manufacturers of generic active ingredients other than the holder of the original patent.

COUNTRIES where this brand/product is marketed: USA, AUS and numerous other countries
GENERIC BRANDS available? Yes, in some countries, but rather few

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

Click here for an overview on the most used antiparasitic feed additives and medicated feeds for livestock and horses.


LARVADEX is a brand from ELANCO that contains cyromazine for the feed-through control of larvae of houseflies and other filth flies in poultry manure.

Cyromazine is a so-called Insect Growth Regulator (IGR) belonging to the group of the Chitin Synthesis Inhibitors (CSI). It was introduced in the late 1970s (by CIBA-GEIGY → NOVARTIS → ELANCO). It is narrow-spectrum larvicide. It is abundantly used in sheep against blowfly strike and in poultry against houseflies and other filth flies. Usage in ruminants and horses is marginal. It is not used in pets. It is also used in agriculture.

Chitin is a component of the cuticle of insects, which is an essential part of their outer skeleton. If chitin is not properly produced, fly maggots die when they attempt the next molt. However, cyromazine does not really inhibit chitin synthesis, but interferes with its correct deposition. The consequence is the same: Fly maggots cannot complete molting and die. Other CSIs such as the benzoylphenyl ureas (BPUs, e.g. diflubenzuron, triflumuron) do actually inhibit chitin synthesis. But whereas BPUs exert this effect on almost all insects, cyromazine is quite specific for Dipterans (flies, mosquitoes, etc.) and some beetles. This makes it less harmful for the environment.

As all IGRscyromazine does not kill adult flies at all, and it does not immediately kill the fly maggots (larvae) either, i.e. it has no knockdown effect. Larvae will die at their next attempt to molt to the next developmental stage, which may take 1-4 days to occur, depending on age of the maggots at the time of treatment, humidity, temperature, etc.

Cyromazine is quite soluble in water, in contrast with many other parasiticides that are rather lipophilic, and is hardly metabolized after being ingested with the feed. It is excreted unchanged, mainly in urine, not in the feces, thus the term "feed-through". In birds, urine is mixed with feces in the cloaca and for this reason feed-through administration ensures that all bird feces get treated with the larvicide. This is not the case in mammals.

In some countries cyromazine is also available for direct treatment of manure and other organic waste in poultry and other livestock premises (e.g. LARVADEX 2SL, NEPOREX).


This article IS NOT A PRODUCT LABEL. It offers complementary information that may be useful to veterinary professionals and users that are not familiar with veterinary antiparasitics. 

Information offered in this article has been extracted from publications issued by manufacturers, government agencies (e.g. EMEA, FDA, USDA, etc.) or in the scientific literature. No guarantee is given on its accuracy, integrity, sufficiency, actuality and opportunity, and any liability is denied. Read the site's DISCLAIMER.

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