CHEMICAL FLEA CONTROL in DOGS & CATS with INSECTICIDES: spot-ons, pipettes, tablets, collars, shampoos, soaps, baths, sprays, powders

Main flea control product categories

Nowadays there are two major product categories for on-animal flea control:

  • For external or topical use:
    • Spot-ons = pipettes = drop-ons = squeeze-ons: hundreds of brands, mostly for monthly administration
    • Collars impregnated with insecticides: dozens of brands, for long-term protection
    • The rest: shampoos, soaps, baths, sprays, aerosols, lotions, powders, etc: thousands of brands; the cheap alternative, rather short protection
  • For internal use:
    • Tablets, pills, chewables, etc.  for oral administration: only a few brands, mostly for monthly administration
    • Liquids for oral administration: very few brands, mostly for monthly administration
    • Injectables: very few brands, for long-term protection

To learn more about general features of parasiticides click here
To learn more about general features of external parasiticides = ectoparasiticides click here
To learn more about delivery forms of parasiticides click here

SPOT-ONS (= pipettes, squeeze-ons, drop-ons) against dog and cat fleas

Spot-ons are a very popular type of flea insecticides. Picture from www.bockonline.ch

Spot-ons are ready-to-use concentrates containing one or more active ingredients with parasiticidal efficacy. Depending on the active ingredient(s) they are effective only against adult fleas, or also against immature stages, against various tick, mite or lice species, against internal parasites such as gastrointestinal worms, heartworm, tapeworms, etc. Most original spot-ons were introduced in the 1990s and 2000s and are responsible for most of the flea control "revolution" of the last 25 years. In the meantime generic spot-on brands have proliferated.

Spot-ons are for topical administration, i.e. on the skin of the pets. They are often sold in single-use squeezable vials or ampoules of different sizes for dogs or cats in a particular weight range. The whole content of a vial is applied on a given "spot" (typically on the neck or on the back). Once applied to the skin, the active ingredient is supposed to spread throughout the body of the pet or is absorbed through the skin into the pet's organism (so-called systemic products).

Both spreading and/or absorption through the skin can be slower or faster, more or less complete, etc. depending on each animal's features (e.g. size, breed, hair coat, behavior, etc.) and also on the non-active, inert ingredients in the product, i.e. on its formulation, which can vary significantly between manufacturers. This is why product quality (and safety!) depends not only on the active ingredient(s), but also on the formulation (this is true for spot-ons and for whatever parasiticide or medicine, veterinary or human).

Most original spot-on brands claim to achieve a strong and fast curative (i.e. therapeutic) effect of established flea infestations, i.e. >90% (often >98%) within 1 to 3 days after a single treatment. Most of them also claim to provide a strong preventive (i.e. prophylactic) effect of about 4 weeks, whereby this preventive effect diminishes progressively from week 1 (often >99%) to week 4 (mostly <90%). As a general rule they deliver.

Most spot-ons are quite resistant to occasional washing and shampooing, i.e. the pet won't lose protection against fleas due to a splash. But repeated splashes or shampooing can indeed diminish the length or protection.

Strategic requirements for successful flea control in dogs and cats

There are certain strategic conditions that ensure successful flea population control in a household when using products for monthly administration (spot-ons, tablets, etc.). If they are not followed, many fleas will be killed, but the problem won't be solved.

And keep in mind, that if you don't perceive a flea problem, it doesn't mean that there are no fleas. There may be a lot of pre-emerged adult fleas in the household waiting for good hatching conditions inside the cocoons.

All dogs and cats in a household must be treated

All dogs and cats can breed fleas. It happens sometimes, that in multi-pet households only one pet "shows" flea problems. This doesn't mean that the other pets don't have fleas, just that they are more tolerant. But all fleas reproduce and re-infest the environment with eggs. Therefore all pets have to be treated consequently.

If there are other small animals (e.g. guinea pigs, mice, rats, rabbits, etc.) in the same household, it is very likely that they have fleas as well and should be treated too. However, most dog and cat flea products are not approved for use on such other pets. In this case ask your veterinary doctor for advice.

Treatments must start at the onset of the flea season

The reason is simple. At the beginning of the flea season, the first generation of fleas hatch out of their cocoons and quickly find a host for blood feeding. These cocoons have overwintered in the environment. This first generation is usually not very numerous, maybe a dozen fleas. But uncontrolled, they will quickly produce thousands of eggs and hundreds of fleas in very few weeks. The few fleas of the first generation usually remain unnoticed by most pet owners. Therefore the first treatment should not wait until a flea problem is "perceived" but must be done as soon as possible: Around April in very cold regions (e.g. Canada, Scandinavia, etc.); already in March or February in less cold regions.

In many warm regions, seasonality is often driven by humidity rather than by temperature. Flea numbers will decline by dry weather and increase in the rainy season. The same rule applies: start the monthly treatments a few months before the problem usually "appears", i.e. before it is usually perceived.

In regions with constant hot and humid weather fleas are usually a year-round problem: it doesn't matter when to start. The key is to treat all pets in the household and to strictly keep the monthly intervals.

Treatment must continue during the whole flea season

In the cold regions of both hemispheres the flea season may last for 4 to 5 months, and the warmer it gets towards the tropics, the longer the season. It is crucial not to interrupt the treatments during the season, even if no fleas are "perceived" after a few treatments. As already explained, hatching of overwintering fleas out of their cocoons is staggered for weeks and even months. And pets can catch fleas outdoors. If such fleas are not killed, they will re-infest the household again. To ensure that they are killed, monthly treatments should not be interrupted.

Most common original spot-on brands for flea control in dogs and cats

The best known original flea spot-on brands are the following:

  • FRONTLINE TOP SPOT, with fipronil, (originally from MERIAL, now BOEHRINGER INGELHEIM); available for dogs and cats worldwide. Introduced in the mid 1990s. Fipronil is a broad-spectrum contact insecticide and acaricide that kills the adult fleas (adulticide) and belongs to the phenylpyrazole pesticides. Besides fleas it also controls some pet ticks and lice. Fipronil is also vastly used in agriculture as well as in public and domestic hygiene. There are numerous generics.
    • Follow-up brands from MERIAL:
  • ADVANTAGE, with imidacloprid, (originally from BAYER, now ELANCO) Available for dogs and cats worldwide. Introduced in the mid 1990s. Imidacloprid is a broad-spectrum contact insecticide that kills the adult fleas (adulticide) and belongs to the neonicotinoid pesticides. Besides fleas it also controls a few lice species, but not ticks. Imidacloprid is also vastly used in agriculture as well as in public and domestic hygiene. There are numerous generics.
    • ADVANTIX with imidacloprid and permethrin. Permethrin is a synthetic pyrethroid added to provide efficacy against ticks. Permethrin is also a broad-spectrum pesticide vastly used on livestock, in agriculture and in hygiene. ADVANTIX is available only for dogs, because permethrin is toxic for cats. 
    • K9 ADVANTIX with pyriproxyfen in addition to imidacloprid and permethrin. Pyriproxyfen is a juvenile hormone analogue, i.e. an insect development inhibitor, which prevents deposited eggs from hatching, because a few adult fleas may survive the imidacloprid treatment. It is available only for dogs in certain countries. Pyriproxyfen is also used in agriculture and hygiene.
    • ADVOCATE = ADVANTAGE MULTI, with imidacloprid and moxidectin. Moxidectin is a broad-spectrum macrocyclic lactone that adds efficacy against all major roundworms, including heartworms, asl well as against several mites and lice species, but is not effective against fleas. Moxidectin is also used on livestock but not in agriculture or hygiene.
    • Follow-up brands from BAYER:
  • PRAC-TIC, with pyriprole, (originally from NOVARTIS, now ELANCO). Available in the EU and other countries, but not yet everywhere, e.g. not in the USA. Only for dogs. Introduced in 2007. Pyriprole is a broad-spectrum contact insecticide and acaricide that kills the adult fleas (adulticide) and belongs to the phenylpyrazole pesticides. Besides fleas it also controls some pet ticks. Pyriprole is not used on livestock, agriculture or hygiene: it is only used on dogs. There are no generics so far.
  • REVOLUTION = STRONGHOLD, with selamectin, from ZOETIS (PFIZER). Available for dogs and cats worldwide. Introduced in the late 1990s. Selamectin is a macrocyclic lactone effective against adult fleas, certain lice, mite and tick species as well as against roundworms, including heartworms. It has a systemic mode of action, i.e., it is first absorbed through the skin into blood and then distributed through the whole body of the pet. There are no generics so far.
  • ASSURITY, with spinetoram, from ELANCO. Available only for cats in certain countries. It has been introduced in 2011. Spinetoram is a semi-synthetic broad-spectrum insecticide belonging to the chemical class of the spinosyns, closely related to spinosad. It is highly effective against fleas, but not against ticks. Spinetoram is also used in agriculture, but not on livestock. There are no generics so far.

Click here to learn more about spot-ons, pipettes, squeeze-ons: efficacy, safety, etc.

COLLARS impregnated with insecticides against dog and cat fleas

Before the introduction of modern spot-ons in the 1990s insecticide-impregnated collars were quite popular for pets against fleas and ticks. Many brands are still available.

Good collars should kill 80-90% of the fleas within 1 week after application and provide about 90 to 70% protection against re-infestation for 8 to 12 weeks, whereby efficacy usually diminishes during the last weeks.

Most collars consist of a plastic or a thick textile strip impregnated with an insecticide that is slowly released to the hair coat around the collar. It spreads more or less rapidly and completely to the rest of the hair coat. All insecticides used in collars kill adult fleas by contact.

Most insecticide-impregnated collars are quite resistant to occasional washing and shampooing, i.e. the pet won't lose protection against fleas due to a splash. But repeated splashes or shampooing can indeed diminish the length or protection.

Such collars contain mostly only one active ingredient, frequently a "veteran" from the following chemical classes:

A weakness of all these collars is that flea resistance to such veteran insecticides is quite frequent worldwide, which can significantly reduce their efficacy and length of protection.

All these pesticides are vastly used on livestock, as well as in agriculture and in public and domestic hygiene.

There are also collars impregnated with "soft" natural insecticides such as natural pyrethrins, d-limonene, linalool, etc.

Clik here to learn more about insecticide-impregnated collars: efficacy, safety, etc.

SHAMPOOS, SOAPS, BATHS, SPRAYS, POWDERS, etc. against dog and cat fleas

A common feature to this category of flea control products is that protection against re-infestation is significantly shorter that spot-ons or collars. Depending on the product, protection won't last longer than 2-4 days. This may be enough to clean a pet from fleas. But not to prevent newly emerged fleas to re-infest the pet. The reason is that most of these products are not resistant to water (shampooing, washing, rain, etc,.) and/or to exposure to sunlight. Such products are often cheaper than spot-ons or collars, but also less reliable.

In addition, whereas the curative efficacy of spot-ons and collars is usually >90%, it is significantly lower (70 to 85%) for these products. Administration is also less straightforward than for spot-ons and collars, which often leads to incorrect use that diminishes the efficacy.

These products are often not resistant to washing and shampooing, i.e., a simple splash may cause lost of whatever protection against fleas.

A further weakness of all these products is that flea resistance to such veteran insecticides is quite frequent worldwide, which can significantly reduce their efficacy and length of protection.

These products contain mostly "veteran" active ingredient from the following chemical classes, sometimes in mixtures.

Many such products contain also "soft" natural insecticides such as d-limonene, geraniol, linalool, pyrethrins, etc. often in mixtures with classic synthetic insecticides and with a synergist.

A further weakness of many of these products is that flea resistance to organophosphates, carbamates, synthetic pyrethroids and natural pyrethrins is quite frequent worldwide, which can significantly reduce their efficacy and length of protection.

Click here to learn more about shampoos, soaps, baths, sprays: efficacy, safety, etc.

TABLETS, PILLS, CHEWABLES, etc. against dog and cat fleas

All products for internal use, including tablets, pills, chewables, etc. contain active ingredients with a systemic mode of action, i.e. once ingested they are absorbed into blood and distributed throughout the pet's body. They reach the fleas during their blood meals, wherever they are biting, which is not always the case for products for external use that act by contact. This means also that they remain unaffected by whatever external influences such as washing, shampooing, rain, exposure to sunlight, dirt, etc. 

Such products are a good option for pet owners that want to avoid getting themselves or their children in contact with pesticides, which is unavoidable when using topical products such as spot-ons, collars, shampoos, sprays, etc.

The best known original brands of flea pills and tablets are the following:

  • PROGRAM, with lufenuron, (originally from NOVARTIS, now ELANCO). Available worldwide only for dogs. Introduced around 1990. Program was the product the launched the "flea control revolution" previously mentioned. Lufenuron is a broad-spectrum insect development inhibitor belonging to the chemical class of the benzoylureas. Lufenuron does not kill the fleas on the pets, but makes that their eggs become sterile. For this reason it should be used as a preventative. If administered to heavily infested pets, since it does not kill them, it will take several weeks until they are free of fleas. Monthly administrations starting at the beginning of the flea season will effectively prevent the development of flea populations in the household. Lufenuron is also used in agriculture. There are a few generics.
  • SENTINEL = PROGRAM PLUS, (originally from NOVARTIS)- Contains lufenuron and milbemycin oxime. Available only for dogs in certain countries.  Milbemycin oxime is a broad-spectrum macrocyclic lactone highly effective against heartworms and the most important gastrointestinal roundworms of dogs. Milbemycin oxime has no efficacy against fleas.
  • SENTINEL SPECTRUM, (originally from NOVARTIS). Contains lufenuron, milbemycin oxime and praziquantel. Available only for dogs in certain countries. Praziquantel is a generic taenicide belonging to the chemical class of the isoquinolines. It is highly effective against the major parasitic tapeworms of dogs.
  • CAPSTAR, with nitenpyram, (originally from NOVARTIS, now ELANCO). Available for dogs and cats worldwide. Introduced in the late 1990s. Nitenpyram is a broad-spectrum insecticide belonging to the neonicotinoid pesticides. Orally administered nitenpyram acts extremely quickly. It can kill all fleas on a pet within 2 to 4 hours after administration, whereas most other products need 24 to 48 hours. However, it has only 1-2 days residual effect, i.e. protection against re-infestation is very short. Nitenpyram is used in agriculture but not on livestock. So far there are no generics.
  • COMFORTIS, with spinosad, from ELANCO. Availabe only for dogs in certain countries. Introduced in the late 2000s. Spinosad is a broad-spectrum insecticide and acaricide of natural origin belonging to the spinosyns. Orally administered spinosad acts against fleas as fast as nitenpyram, i.e. it kills most of them within a few hours after administration. And it provides up to 4 weeks protection against re-infestation. Spinosad is used on livestock as well as in agriculture and hygiene. So far there are no generics.
  • BRAVECTO, with fluralaner, from MERCK (MSD) ANIMAL HEALTH. Availabe only for dogs in certain countries. Introduced in 2014. Fluralaner is one of the newest insecticidal active ingredients from the chemical class of the isoxazolines. With a unique 3-month claim against ticks and fleas. There are no generics.
  • NEXGARD, with afoxolaner, (originally from MERIAL, now BOEHRINMGER INGELHEIM). Availabe only for dogs in certain countries. Introduced in 2014. Afoxolaner is one of the newest insecticidal active ingredients from the chemical class of the isoxazolines.
  • NEXGARD SPECTRA, with afoxolaner and milbemycin oxime, (originally from MERIAL, now BOEHRINMGER INGELHEIM). Availabe only for dogs in certain countries. Introduced in 2015. For monthly administration against ticks, fleas, several roundworm species and for heartworm prevention.
  • SIMPARICA, with sarolaner, from ZOETIS. Availabe only for dogs in certain countries. Introduced in 2016. Sarolaner is one of the newest insecticidal active ingredients from the chemical class of the isoxazolines.
  • CREDELIO, with lotilaner, (originally from NOVARTIS, now ELANCO). Availabe only for dogs in certain countries. Introduced in 2017. Lotilaner is one of the newest insecticidal active ingredients from the chemical class of the isoxazolines.

Click here to learn more about pills, tablets, etc: efficacy, safety, etc.

LIQUID formulations for injection or oral delivery against dog and cat fleas

There are very few injectables or liquid oral formulations against fleas of pets. To my knowledge the only ones to be reasonably reliable are the following ones:

  • PROGRAM ORAL SUSPENSION with lufenuron, from NOVARTIS, now Elanco). For oral administration only to cats. Available in most countries. Introduced in the mid 1990s. Lufenuron is a broad-spectrum insect development inhibitor belonging to the chemical class of the benzoylureas. Lufenuron does not kill the fleas on the pets, but makes that their eggs become sterile. For this reason it should be used as a preventative. If administered to heavily infested pets, since it does not kill them, it will take several weeks until they are free of fleas. Monthly administrations starting at the beginning of the flea season will effectively prevent the development of flea populations in the household. Lufenuron is also used in agriculture.
  • PROGRAM 6 MONTHS INJECTABLE, with lufenuron, from NOVARTIS, now Elanco). Only for cats. Available in certain countries. Introduced in the late 1990s. A single injection is enough to cover the whole flea season in most regions with a cold winter.

Be aware that ivermectin products are always inadequate for controlling fleas! Unfortunately, with the proliferation of ivermectin brands, products of doubtful origin may appear that claim to control fleas on pets or livestock. They don't. The only macrocyclic lactone that controls fleas at the therapeutic dose is selamectin (active ingredient of STRONGHOLD = REVOLUTION). All other macrocyclic lactones do not control fleas.

Click here to learn more about injectables: efficacy, safety, etc.
Click here to learn more about drenches: efficacy, safety, etc.

ENVIRONMENTAL CONTROL of dog and cat fleas 

On-animal control products may not be sufficient for controlling flea populations in a household and additional off-animal control measures may be required, e.g. treating carpets, rugs, furniture, upholstery, lawns, etc. with adequate pesticides.

This was normally the case before the "flea control revolution" of the 1990s, because the products then available for on-animal treatment were not potent enough. Nowadays, most modern flea control products for monthly administration are strong enough to make off-animal environmental treatments superfluous. However, such modern products are expensive and not affordable for everybody. If such products cannot be regularly used, environmental control may be unavoidable in order to really control flea populations.

In most countries only certified Pest Control Operators (PCOs) are allowed to perform environmental flea control with pesticides. The reason is that the use of the required pesticides is restricted to professionals for safety reasons. In fact, large-scale use of pesticides indoors in households or other premises is not trivial and bears significant safety risks if done improperly.

Most products for environmental flea control used by PCOs contain classic synthetic pesticides of the following chemical classes:

Most of these products are available only for PCOs in the form of concentrates. They have to be correctly diluted before usage, and application requires specific equipment and appropriate training. Some of these concentrates are notably more toxic than the ready-to-use products available for on-animal control. Many of these products are the same that are used against cockroaches, termites, and other household pests.

If you ask a PCO for flea control in your household, the key for successful environmental flea control is to adequately treat those places were immature flea stages (eggs, larvae, cocoons) tend to concentrate, i.e. those places the pets prefer for sleeping and resting.

  • Indoors: typical places to treat are sleeping places of the perts (cradles, nests, etc.), dark corners below furniture, in bathrooms, basements, cellars, etc. Carpets, rugs, mattresses, cushions, textile upholstery, etc. are also ideal flea breeding places. Dry pet or livestock bedding and dry sandy soils are also excellentflea breeding environments. Hard and plastic flooring (stone, tiles, wooden parquet, etc.) are much less appropriate for flea breading. However, gaps or cracks (e.g. between parquet slates) filled with dirt can also support flea development.
  • Outdoors. Key places to treat are in and around doghouses, hiding places below the house, in dark corners under tress or brushes. Vehicles used for pet transport should also be treated.

After a first treatment, the level of flea infestation has to be monitored to estimate the need for further treatments. This can be done regularly combing your pet for fleas and recording the numbers caught.  It can also be done with sticky rolls that you can roll over carpets or furniture you believe most infested with fleas. Another monitoring method is to walk around the house with long white socks and count the fleas that jump onto the socks.

A weakness of many of these products is that flea resistance to organophosphates, carbamates, synthetic pyrethroids and natural pyrethrins is quite frequent worldwide, which can significantly reduce their efficacy and length of protection.

FLEA RESISTANCE to insecticides

Resistance of the cat flea (Ctenocephalides felis) and other flea species to veteran insecticides (carbamates, organophosphates, organochlorines, synthetic pyrethroids, etc.) is widespread worldwide. Resistance to synthetic pyrethroids may be that high, that it not only reduces the efficacy or the length of protection, but it makes the product completely useless. Resistance to organophosphates and carbamates it usually less strong and affected products will provide some level of control.

This means that if a product containing such pesticides does not meet the expectations raised in the label, it can be due to resistance. This may be the case for numerous, shampoos, soaps, sprays, aerosols, baths, insecticide-impregnated collars, etc. But don't forget that most product failures are due to incorrect use.

So far there are no reports on confirmed field resistance of fleas to newer insecticides such as those used in most flea spot-ons or tablets (e.g. lufenuron, nenonicotinoids, phenylpyrazoles, selamectin, spinosyns, etc.). But nobody knows what will happen. The massive use of flea insecticides in many countries puts the flea populations under a tremendous selective pressure. The experience shows that this is the best way to select for resistance fleas. So the question seems to be not whether resistance to the newer insecticides will appear, but rather when and where it will be appear.

To diminish the risk that it appears precisely in your household, it is highly advisable to regularly change the flea control products you are using (e.g. every 2 or 3 years) making sure that the new product has a different mode of action, i.e. it belongs to a different chemical class than the previous one. If you have used a product with a phenylpyrazole (e.g. fipronil or pyriprole) for several years, consider changing to a product with a neonicotinoid (e.g. imidacloprid, dinotefuran), a spinosyn (e.g. spinosad or spinetoram), a benzoylurea (e.g. lufenuron), a macrocyclic lactone (e.g. selamectin), an oxadiazine (indoxacarb) or an isoxazoline (afoxolaner, fluralaner, sarolaner); or vice-versa. This periodic alternation of active ingredients with different modes of action to delay resistance is called rotation. An reasonable alternative to rotation is using a product that contains a mixture of two active ingredients with different modes of action (e.g. a flea killer combined with an insect development inhibitor).

If a product fails to meet the expectations, it is almost impossible for a pet owner to find out whether it is due to resistance, to incorrect use of the right product, or to correct use of the wrong product. Since there are so many alternative brands with many active ingredients and mixtures, the best solution is often to simply try another product with an active ingredient of a different chemical class. If a second product of a different chemical class also fails, chances are high that failure is due to incorrect use.

Learn more about parasite resistance and how it develops.

Click here to leran more about natural control of fleas, i.e without synthetic chemicals.

  • Click here to view the article on NATURAL CONTROL of fleas in dogs and cats (traps, natural insecticides, medicinal herbs, vaccines, biological control, etc.).
  • Click here to learn the basics of flea biology in order to have a better chance to get rid of them. Knowing how fleas make their living (where they live, how they reproduce, how they behave, etc.) will help you to choose the right flea control measures among the many options available.

A littel bit of recent flea control history...

In the last 25 years, chemical control of fleas on pets has experienced a real revolution with dramatic improvements in efficacy and convenience (and prize...). Flea control on pets has become the largest Animal Health submarket, worth several billion USD a year. 

Until the late 1980's flea control products for on-animal use were not too effective and quite unreliable, but rather cheap. They were sold mainly over the counter (OTC) in pet shops, supermarkets and the like. They contained veteran insecticides such as organophosphates, carbamates and synthetic pyrethroids. Even earlier organochlorines were used as well. Since these products for on-animal use were not too effective, there was a strong need for complementary off-animal treatment of the household environment, which was accomplished by professional Pest Control Operators (PCOs) using the same veteran insecticides to treat carpets, furniture, lawns, etc.

Several multinational companies (Bayer, Merial, Novartis, Pfizer, etc.) discovered the huge latent potential and started a race to conquer and to develop this market. This race is still going! They did and still do it with absolutely first priority over whatever other potential veterinary markets, especially over the livestock market. Hundreds of millions of USD have been invested in research, development and advertising on such new flea products. The result is an unprecedented arsenal of new products for flea control introduced in the last 25 years, whereas progress on livestock parasiticides has been miserable.

In addition, for strategic and regulatory reasons, almost all multinationals decided to marketmost of these new products as prescription-drugs through vets and pharmacies, whereas the old products were all sold prescription-free through OTC channels. By doing this, the new flea products became professional veterinary medicines and not simply better OTC flea pesticides. The bottom line is that this allowed much higher prices and margins, without price wars among competitors. It worked! Every pet owner knows that if it is true that many modern flea products are very effective, it is equally true that they are rather expensive.

In the meantime, generics of those highly potent flea products have multiplied and prices are going down. But the race continues, for the time being towards all-in-one flea products, i.e. control of adult fleas + flea larvae + ticks + mites + lice + roundworms + heartworms + tapeworms + ... with one spot-on, or one pill. We are not yet there, but quite close.

A collateral effect of this development was that sales of cheap and veteran OTC-products plunged, and the environmental flea control business of PCOs almost disappeared, because the new flea products for on-animal use are that effective, that environmental flea control is only seldom required.

Parasitic Insects