Biological control involves the use of a pest’s own natural enemies (parasites, predators and pathogens) – whether introduced or otherwise manipulated – to suppress the pest populations to an acceptable level. The word “pest” is used here in a broad sense, which includes diseases, insects, mites, nematodes and weeds and/or invasive alien plants.

While in principle there is little difference between the biological control of diseases, insect pests and weeds, it is usually accepted that a far higher degree of host-specificity is required for a weed-biocontrol agent than for a pest-biocontrol agent. Most pest-biocontrol agents kill their host directly, while suppression of weeds could take place by killing or weakening the weed, by reducing its reproductive capacity, or by creating an avenue for infection by pathogens.

Different techniques can be used in biological control:

  • The technique most often used for the control of insect pests and weeds is referred to as classical biological control. It involves the introduction of natural enemies from the native range of the pest or weed from its country of origin, after which the natural enemies become established in the new country, build up their numbers and remain present in the new environment.
  • Inundative biological control involves the repeated introduction and release of large numbers of natural enemies.
  • Augmentative biological control describes actions that increase the populations of natural enemies.
  • Conservation biological control refers to environmental modification to protect and enhance natural enemies.

Biological control cannot be expected to solve all pest or weed problems in a particular situation, but should nevertheless be the core around which pest or weed management systems are built. Biological control is often only possible within the framework of an integrated pest management (IPM) system.

Why the need for an alternative?

Pesticides have revolutionised agriculture, increasing yield and improving harvest quality, but their leftover stockpiles can contaminate the environment and endanger human health. If a pesticide has the potential to kill, then it also carries a risk to the environment. Some pesticides are harmful to people and the environment because they remain in the soil, air and water for a long time, are easily dispersed by water and air, and concentrate in the high-altitude, low-temperature regions.

Irresponsible use of non-selective pesticides eliminates not only the target pest but also many beneficial organisms that play an important role in garden, crop or natural ecosystems. Some of the answers to our pest problems may be right under our noses, such as the tiniest microbe in the soil, a fungus, bacterium, virus or nematode or one of the many parasitic or predatory insects, reptiles, birds and mammals in our environment. Organisms that we might consider “pests” have a place in the scheme of things. Without them there would be none of the wonderful birds, spiders and reptiles on our farms.

Programmes which promote the responsible use and disposal of agricultural chemicals are run by CropLife SA and CropLife International (see the “Chemicals in agriculture” page).

Biological control of agricultural pests using predators and parasites (including IPM)

Biological control of agricultural pests usually forms part of an integrated pest management (IPM) programme. IPM refers to the ‘integration of two or more control strategies’ for suppression of the pest below a given threshold level. Many purely chemical strategies are also aimed at reducing pest populations below a threshold level and not at eliminating entire populations of the pest. IPM is based on the assumption that it is not necessary or cost effective to try to eliminate an entire population of pests.

Instead, threshold levels are established to determine when control is necessary to bring pest population levels down. When the number of pests reaches a threshold level, a pesticide may be used to prevent excessive crop damage or loss greater than the cost of preventing the damage. IPM programmes require a thorough understanding of various techniques such as biological, cultural, mechanical and chemical control methods. Some actions needed in support of integrated pest management include correct pest identification, pest monitoring, and determination of economic injury levels.

Conservation biological control


This refers to environmental modification or other actions that are taken to preserve, protect and enhance natural enemies.


Spiders naturally suppress pest populations and are self-renewable, minimising costs to farmers. As you use fewer chemicals you may increase the effectiveness of spiders against pests. The benefit may be much more than just saving the cost of the chemical and application.


However, if you do use pesticides, minimise the effect on predators by avoiding synthetic pyrethroids, which are among the most toxic to beneficial predators. Insect growth regulators are among the least toxic to spiders. Systemic insecticides, which require the consumption of plant material for exposure to toxicity, affect natural enemies less. Softer pesticides allow the natural conservation of predators. Denser populations of spiders slow the rate of pest recovery so that fewer applications of pesticide are required in a season. Ten times more ground-dwelling dwarf and other spiders live in organic fields and fields sprayed with soft pesticides than in fields sprayed with broad-spectrum pesticides.


Once spiders are established in the environment, they are a self-renewable resource.


Even on a conventional farm, which uses chemical pesticides, predators kill most pests most of the time and when pesticides devastate natural enemies of potential pests, insects that were of little economic importance can become damaging pests. When a non-toxic control method is used, spiders reduce the numbers of and damage caused by potential pest species.

Inundative biological control and biopesticides

This technique is used for natural enemies that do not become permanently established in the new environment, and therefore large numbers have to be reared somewhere else and released periodically where they are required. There are some 30 commercially available species of predators and parasitoids, such as spiders, mites, beetles and parasitic wasps, which seek out and kill insect pests. They are mass-reared and sold by companies called ‘insectaries’.

The use of biopesticides is a special type of inundative biological control. The technology is such that we can “formulate” living organisms such as fungi, bacteria and viruses just as we would formulate chemical pesticides. These live “active ingredients” can be applied to crops with similar application methods to traditional pesticides. The actual period that these organisms remain active determines the frequency of application, as is the case with the active ingredient of traditional pesticides. Microbial control agents or pathogens such as fungi are available for the control of weeds, insect pests and diseases of crops.

Role players




Training and research

  • Absolute Neem Oil Tel: 041 466 0129
  • ARC-Plant Protection Research (i) Biological control of agricultural pests: Dr Roger Price – 012 356 9817 (ii) Classical biological control of invasive alien plants: Hildegard Klein – 012 356 9841 (iii) Conservation biological control: Dr Ansie Dippenaar – 012 808 8247
  • ARC-Small Grains Dr Justin Hatting Tel: 058 307 3400
  • Other ARC campuses in the Horticulture business division do research on the biological control of pests in certain crop situations. Consult
  • Biological Crop Health Tel: 083 631 9952 Research: Microbial Crop Protection. Efficacy evaluation is done of biological control products under field and greenhouse conditions.
  • HORTGRO Science Mr Matthew Addison Tel: 021 882 8470
  • Koppert Biological Systems Tel: 012 253 2479
  • North-West University (Potchefstroom) Unit for Environmental Sciences IPM Programme johnnie.vandenberg [at]
  • Rhodes University Department of Zoology and Entomology Prof Martin Hill – 046 603 8712
  • South African Sugar Research Institute Dr Des Conlong Tel: 031 508 7400
  • Stellenbosch University Department of Conservation Ecology and Entomology (i) Prof Michael Samways Tel: 021 808 3728 (ii) Dr Antoinette Malan – 012 808 2812 Malan is South Africa’s Entomopathogenic nematodes (EPN) expert.
  • University of Cape Town Department of Zoology Tel: 021 650 5556
  • University of KwaZulu-Natal Department of Plant Pathology Tel: 033 260 5524 Conducts research on biological control of crop pests, diseases and abiotic stress.
  • University of KwaZulu-Natal School of Life Sciences Dr Terry Olckers Tel: 033 260 5139
  • University of Pretoria Forestry and Agricultural Biotechnology Institute (FABI) Tel: 012 420 3938/9
  • University of the Witwatersrand Prof Marcus Byrne Tel: 011 717 6491

Information Core for Southern African Migrant Pests (ICOSAMP) is a regional co-operative initiative between officers working on migrant pests in different SADC counties. Find information on


Websites and publications

Visit the websites listed earlier on this page.

Find the ARC-Plant Protection Research (ARC-PPR) on Posters, CD-roms, publications and other materials are available. Write to infoppri [at]


Relevant publications:


  • PPRI Leaflet Series: Weeds Biocontrol – contact Hildegard Klein, tel: 012 356 9841; e-mail kleinh [at]
  • Dossiers on Biological Control Agents available to aid Alien Plant Control– contact Hildegard Klein, tel: 012 356 9841; e-mail kleinh [at]

 Some articles

Our appreciation to Hildegard Klein at the ARC-PPR for the notes she made available to the project, and to Michelle Paterson for feedback on the draft chapter.

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