Can biological control replace chemicals?

David Dent of CABI Bioscience argues that the answer to this question is not a simple ‘yes’ or ‘no’ but a qualified ‘yes, but’ and ‘no, except’. Biological and chemical agents are different. 

Key differences
Chemicals are mainly used as herbicides, fungicides and insecticides in the UK with annual sales in agriculture and horticulture (for 2001) of 11,817, 3,628 and 857 tonnes of active ingredients respectively (1).These chemicals characteristically have good storage, relatively wide spectrum of activity, fast speed of kill, relatively short persistence so need frequent applications, potential for environmental harm and toxicological concerns. 
    In contrast, biological control agents tend to have relatively poor storage, high target specificity, slow speed of kill, potentially long persistence through secondary cycling and hence lower frequency of application, are environmentally friendly and low hazard for humans and livestock. Biological control agents include pathogens (bacteria, fungi, viruses) and entomopathogenic nematodes usually formulated as biopesticides, and insect predators and parasitoids (small wasps that parasitize insects). Biocontrol can be applied through introductions, augmentative releases, innundatively as biopesticides or through conserving existing field populations.
    However, there has been a tendency with biocontrol agents and particularly biopesticides, to develop and use them just as if they have the same properties as chemicals. For example, the development and use of Bacillus thuringiensis (Bt) which is the best selling biopesticide and is used largely like a chemical insecticide. Technical constraints at present limit the number of mycoherbicides available to replace the large use of chemical herbicides while the opposite is true for insecticides where a number of effective biopesticides exist.
    The effectiveness of a biocontrol agent depends on two factors: its capacity to kill and to reproduce on pests (compounding its killing action); in ecological terms, its functional and numerical responses(2). Currently biopesticides based on viruses and fungi that have the potential for persistence and the compounding benefits of numerical responses, have been developed using the traditional chemical pesticide model involving a quick kill, low persistence and frequent application. In this way, all the shortcomings of these biopesticides relative to chemicals emerge, and few of the benefits(3). Hence, there are many opportunities to exploit the ecological benefits of biopesticides that have yet been little explored. 
    Biologicals cannot be successfully used against all pests. For instance, insects that feed directly on a harvestable products are considered low threshold pests because they cause damage at very low pest densities(4) e.g. Cydia pomonella on top fruit. The use of biocontrol agents for the control of such low threshold pests is generally not feasible because they are too slow-acting to prevent damage (although infection by microbial agents will sometimes reduce feeding activity by an insect). Whereas with high threshold pests, that feed, for instance, on foliage or stems and cause little yield loss at low pest densities are highly amenable to biological control. An example is the red spider mite Panonychus ulmi. 
    Biocontrol agents can be used effectively against a whole range of high threshold pests including aphids, whiteflies, stemborers, leaf miners, locusts and grasshoppers. Hence, there are specific opportunities for use of biological control agents but as a group they do not provide a panacea as alternatives to chemical pesticides.

The biocontrol market
Biological products currently represent just 1% of the world market, and 80% of that is taken by one product: Bt. Even though this is the case, some commentators have estimated that biological control products could replace at least 20% of chemicals, a market valued at US$7 billion(5). For this to be possible however, the financial, regulatory and technical support, to develop and expand the industry would need to be forthcoming.
    Biocontrol manufacturers are not well equipped to develop markets. Most are small enterprises with small turnovers and just one or two products aimed at niche markets. They do not have the resources to mount international distribution, sales and extension programmes for their products. There is also very little general understanding of the capability and benefits of biocontrol to drive demand by farmers or consumers. Essentially while the knowledge and capability exists, it remains immobilised.

Regulatory discrimination
EU legislation and prohibitive registration costs through the UK’s Pesticide Safety Directorate (PSD) are discouraging the development and commercialisation of many promising new products. One reason is that the same regulations and evaluation criteria are applied to biopesticides as to new chemicals. This means that such biologicals are disadvantaged because while they are undoubtedly safer and provide longer term, more sustainable pest control, control is usually less immediate and their effectiveness is called into question. Cost of registration is also an issue. The cost of dossier evaluation by the PSD is £44,700 and £94,700 for biopesticides and chemical pesticides respectively. The cost of registering biopesticides is vastly disproportionate if one considers the likely market size of these specialised niche products. Because of their specificity (and hence environmental safety) the market size of a typical biopesticide is less than £6.4 million (excluding Bt), whereas imidacloprid (a relatively new chemical insecticide product) has an estimated market size of £360 million (Bateman in press). 
    In the USA, Germany, Holland, Switzerland, Spain and France biopesticides enter a fast track lower cost registration process that has aided the development of the biocontrol industry in these countries. The situation in the UK is preventing development of the industry and use of biopesticides. For instance, an application to the UK government for registration of a biopesticide based on the fungus Beauveria bassiana has been waiting for a licence for six years. And yet, this product is already licensed in Spain, Italy, Greece, Mexico, Argentina and the USA, and is used as a matter of course on organic produce imported into the UK from these countries. 

Conclusion 
The use of biologicals can substitute for some but not all chemicals, with particular opportunities in the short term for replacement of chemical insecticides. However, biologicals are unlikely to ever replace chemicals where a fast kill is required for crops such as fruit and vegetables where high quality standards are required. The characteristics of fungal and viral based biopesticides that make these products superior to chemicals have yet to be fully exploited. The regulatory environment provides a major constraint to the development and use of biologicals as alternatives to chemicals.

References
1. Industry mergers cause pesticide export crash in UK, Agrow No. 401, 31 May 2002.
2. Thomas M and Waage JK, Integration of Biological Control and Host Plant Resistance, TCA Wageninigen/CAB International,1996, UK.
3. Waage, JK, Biopesticides at the crossroads:IPM products or chemical clones? BCPC Proceedings No.68, Microbial Insecticides: Novelty or Necessity, April 1997, p11-19.
4. Solomon MG, The role of natural enemies in top fruit, Proceedings of the Symposium on Insect Control Strategies and the Environment, Amsterdam, 1989, p70-85.
5. Blum B, Blocked opportunities for bio-control. Pesticides News 57, September 2002.

Edited presentation to the Pesticide Challenge conference, November 2003, Dr David Dent, CABI Bioscience, d.dent@cabi.org

[This article first appeared in Pesticides News No. 58, December 2002, page 17]