4.9 Biological control methods (and organic production)

As discussed in Chapter 3, there is no reason why the precautionary principle cannot be consistent with GAP: provided that it is under-pinned with rigorous science and, with available land becoming increasingly scarce, not a threat to productivity. 

GAP/IPM programmes rely heavily on the natural enemies, especially to keep insect pest populations in check where possible, with judicious use of pesticides only when needed. 

Withdrawal of older, especially broad-spectrum AI has brought about increasing recognition of biological agents as potential substitutes.

Amongst the practical issues in organic agriculture, is establishing precisely which pest management interventions are permitted or otherwise.

Advice can even be conflicting as the editors of the Manual of Biocontrol Agents [1] have found. 

A useful guide to compatible management methods is on https://biocontrol.entomology.cornell.edu/index.php 

[Sept 2025: Another useful resource is the CABI BioProtection Portal]

Biological control (BC) of pests has had a long history of highly cost-effective success, but there have also been many cases of failure or incomplete control.

In practice, BC involves the active or passive deployment of three classes of organisms (‘the 3 Ps’): parasitoids, pathogens and predators.

There are various approaches to implementation [2], and important strategies are:
 

• Classical’ biological control, where a co-evolved agent is taken, very often from the area of origin of the target disease (pest), and released in a way that it can multiply and reduce host population levels to a low level. Although there are many entomological examples (e.g. parasitoids are often the most effective solution to invasive Homopteran outbreaks), cases of successful classical BC against other pest categories are rare.

• Inoculation biological control: where an agent is released with the expectation that it will multiply and control the pest for an extended period, but not permanently. Whereas classical BC is also inoculative, inoculation biocontrol is usually used for situations such as the introduction of parasitoids and predators into glasshouses and where the older term ‘augmentation BC’ may not give a clear understanding of the ecological process taking place.
• Biopesticides: a form of inundative biological control. The term “biopesticide” is most useful when applied strictly to living microbial control agents which:
  • 1. are specific as individual products and thus confer some environmental advantage (unlike many but not all chemicals), and
  • 2. have a limited period of activity - and are therefore usually used with normal pesticide application techniques (unlike certain other biological control agents).
• Conservation of natural enemies: one of the more indirect advantages of not using broad-spectrum pesticides is that control of a pest may possibly be enhanced by preservation of its natural enemies.