Biological control of parasites means controlling them with other natural organisms that are their natural enemies.

There are three major types or organisms that are natural enemies of parasites, including veterinary parasites:

  • Predators: Other animals that just feed on the parasites, e.g. birds, ants, beetles, etc. that feed on ticks, flies, maggots, etc.
  • Parasitoids: Mainly insects (mostly wasps and flies) that lay their eggs on the parasites. The larvae that hatch out of these eggs feed on the tissues of the parasite that is ultimately killed. They can be considered as "parasites of the parasites".
  • Pathogens: Microorganisms such as bacteria, fungi, viruses, worms, etc. that infect and kill the parasites. They can be considered as "diseases" of the parasites.

Some organisms that are used against certain parasites are not "native" natural enemies of that particular parasite in a given region, but have been imported from other continent; or the original enemies have been modified (selective breeding, genetic manipulation, etc.).

Whatever controls parasites without synthetic chemicals is often put into the "biological control" basket by many non-specialists: e.g. vaccines, herbal medicines, natural chemicals (e.g. pyrethrins), etc. As a consequence there is often a confusion between so called "bio-control", "bio-products", "bio-pesticides", "bio-parasiticides" (and whatever gets the prefix "bio") and true biological control, particularly in the mass media and in advertising materials.

The combined use of vaccines, herbal medicines, natural products, physical measures and other "non-chemical" approaches, together with the strategic usage of synthetic-chemicals (pesticides and/or veterinary medicines) is called Integrated Pest Control  (IPC) or Integrated Pest Management (IPM) (or its derivatives: Integrated Worm Control, Integrated Flea Control, Integrated Tick Control, Integrated Fly Control, etc). Click here to learn more about Integrated Pest Control

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What to expect from biological control of veterinary parasites?

Honestly, not too much against parasites of livestock; virtually nothing against parasites of dogs and cats.

There are thousands of research papers on the natural enemies of veterinary parasites that could be candidates for their biological control. Unfortunately, for the overwhelming majority of such enemies promising results in the laboratory have not been confirmed under field conditions with natural infestations. Natural enemies may reduce the parasite population to some extent, but usually efficacy is not comparable with the blunt effect of most current commercial parasiticides. With a few exceptions, this means that most farmers or pet owners are not likely to be willing to pay for the "weak" efficacy that such methods would achieve today.

In fact, whereas most farmers and pet owners usually expect a "quick fix", i.e. a curative or therapeutic efficacy on the current infection of a particular animal, biological control means mainly a "slow fix" of the parasite population in the environment of the animals, with little or no immediate effect on animals actually infected at the time when measures are taken.

In addition, biological control is often considerably more sophisticated than chemical control and requires appropriate training. Such training is usually provided in courses where participants learn during several days how to identify the parasites and their enemies, how to monitor the populations, how they develop, etc. It is not trivial and it is time-consuming.

A serious difficulty in numerous less developed countries is that neither parasitoids nor parasite pathogens are commercially available. The reason is that both parasitoids and pathogens are biological materials that require specific manufacturing and distribution logistics, very different from those for synthetic chemicals. A box with hymenopteran wasps to control flies cannot be stored for months in a warehouse, or exposed to high or low temperatures during transport.

A practical limitation of using species-specific predators and/or parasitoids is that if the parasite population diminishes, the natural enemies will also diminish, simply because they will lack food or substrate for larval development. As a consequence they often have to be released when the parasite population starts to increase again, typically at the beginning of the parasite season.

Another disadvantage of biological control is that most natural enemies are rather species-specific, but many field problems are due to different parasite species that occur simultaneously: e.g. flies and ticks, lice and mites, roundworms and flukes, etc. If one parasite can be controlled with its natural enemies, other parasites may still require chemical products.

But there is hope that the enormous research effort (mostly in universities and other public institutions) will progressively result in effective practical solutions. Hopefully affordable solutions that can compete with chemical control, which is likely to become more and more expensive due to resistance of the parases to parasiticides. However, for most veterinary parasites this is not a matter of months or years, but a matter of decades.

Finally, be aware that biological control products (e.g. parasitoid wasps, fungal spores, etc.) are not submitted to the same regulations than chemical pesticides or veterinary medicines. Regulations for these "biological products" are usually much less strict than those for chemicals. This also means that efficacy under field conditions or quality standards may not be as reliable as those of pesticides or veterinary medicines.