Enzo Casagrande and Owen T. Jones
Agrisense BCS Ltd, Mid Glamorgan, CF37 5SU, United Kingdom
Abstract - The use of sex pheromones for mating disruption of Lepidopteran pests of agriculture has, over the last decade, become an important component of integrated pest management packages in a number of crops. Our company has been involved in the commercialisation of at least four major pest management products based on this technology, namely Pectinophora gossypiella in cotton, Chilo suppressalis in rice, Rhyacionia buoliana in forestry and Keiferia lycopersicella in tomatoes. A number of other product development projects have been started with other species but have been discontinued for a range of reasons. During the last decade we have observed several common themes which have emerged as problems during the product development and commercialisation process for mating disruption products. These have included factors such as the formulations used, agronomic constraints, the pest's biology and socio-economic factors. This paper examines the problems encountered and suggests keys to how such problems can be overcome, together with indicators of how mating disruption technology may evolve in the future.
Key words - sex pheromone, mating disruption, integrated pest management, commercialisation
Historical perspective
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Pheromones - the perfect IPM solution! This was a commonly heard statement in the 1970's and early 1980's. Pheromones are species specific, have very low toxicity, they don't even harm the target insect and are "natural" - in the eyes of the general public, although the commercially used materials are synthetic copies of the natural product (Hodosh et al. 1985). At a time when insect resistance to conventional pesticides is of widespread concern and insecticides are constantly implicated as causing environmental damage, destruction of beneficial predators and cause explosions of secondary pests, pheromone-based pest control looks like the perfect solution.
In order to facilitate the introduction of pheromone-based technology, regulatory authorities have generally been very flexible in their data requirements given the benign nature of the technology. While demanding that control products based on pheromones be registered, such authorities usually give them an easy passage through the regulatory process compared to standard insecticides and their use for monitoring is usually exempt from any kind of regulation (Ridgway et al. 1992).
The scene in the mid 1980's was therefore set for success. However, it is now well over 20 years since the first mating disruption strategies were developed and shown to be effective in the field, still the market place has not experienced an explosion in the use of such technology. Under normal circumstances this should be by now an insect control technology which is approaching maturity. What therefore prevented the technology from taking hold in the market place on a large scale?
What have we learnt over the past 20 years?
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The basic principles
Mating disruption aims at preventing males from finding unmated females, thus leaving the females unfertilised and incapable of laying viable eggs.
It seems to work well when: (1) insect populations are relatively low; (2) the target insect is not very mobile or dispersive; (3) the treated area is relatively large and/or isolated from outside sources of the pest; area-wide pheromone treatment programmes have been particularly successful; (4) the target insect is a moth, although there are some cases of mating disruption that have been achieved with hemipteran pests, but they are not widely documented in the literature. ?
It seems to fail when: (1) populations are high, presumably as a result of random encounters between males and females which result in mating; (2) the target insect is mobile and capable of dispersing locally over significant distances or is migratory; (3) the areas treated are too small, have very irregular boundaries, or are poorly isolated from surrounding crops with populations of the target insect; (4) there have been errors in application - either the product was not applied evenly within the crop or it was not applied at the correct time, most commonly, the product is applied too late; (5) no apparent reason - this is probably the most concerning factor; there are occasions when it is seemingly impossible to determine the cause of a control failure given our current level of knowledge of the technology.
The net result of all these limitations is that, while there are a few products against certain pests that work very well, there are many others, either commercialised or under development, which are still questionable.
From the experience we have gathered over the last 12 years we believe the key factors for success are: (1) gaining an understanding of the principles that limit pheromone use, both technical and commercial and (2) combining this with a sound knowledge of the target pest ecology and behaviour. Since this has not always been done, pheromone mating disruption has gained, perhaps unfairly, a reputation for not being robust enough for general use.
A recurring problem with using pheromones for mating disruption control of insect pests is the cost of the product to the end-user. The active ingredients are difficult to produce and are often very expensive. The demands on the controlled release formulations are often very high. Formulations are expected to give a constant release and protect the active ingredient for periods of up to 6 months.
Minimising active ingredient costs is critical. This can be done by either reducing the manufacturing cost of the active ingredient and/or reducing the quantity used in the field. Development of economic synthetic routes for pheromone components is the key to reducing product costs. The pheromone is usually by far the most expensive part of the formulation and any changes in active ingredient cost will have a significant impact on the final product cost.
Being basic in the manufacture of a pheromone and having a low cost synthetic route will often determine commercial viability of a project. In the case of the pink bollworm (Pectinophora gossypiella) , our company has been involved for a number of years in producing mating disruption products for its control. Our decision to pursue this project has to a great extent been determined by the fact that we have patented technology which produces the pheromone components in a very cost-efficient manner (Banasiak & Byers 1990).
Minimising the amount of active ingredient required for field application may be almost as critical as the cost of the active ingredient itself. This involves not only finding the minimum effective rate of pheromone use but also delivering it into the air around the crop in the most efficient manner. This is where a good controlled release formulation is vital. There is always a risk in this area that companies will, in order to achieve acceptable margins in competitive situations, cut the active ingredient rate to below a level which has a good safety margin and thereby compromise the performance of the product.
To make the most of the pheromone applied in the field, a good formulation is needed. Such formulation technology aims to trap the pheromone inside the dispenser, protect it from degradation by environmental factors and release it at a controlled rate for the required period in the field. Over the years different companies have found different solutions to achieve this. Cross-linked polymer matrixes, capsules, sandwiched polymer layers, hollow tubes, semipermeable membranes, micro-encapsulations and extruded polymers to name but a few have been used (Weatherston 1990). Broadly speaking however, they tend to fall into two categories - those that are applied by hand and have a long duration (up to 180 days) and those that are applied using spray application technology and are usually of a much shorter duration in the field (up to 30 days). The development of season-long hand-applied formulations has undoubtedly been a significant advance in the last ten years and has lead to the adoption of the technology over large areas in a number of crops. The fact that such formulations are not so demanding in terms of application skills, timing and continued vigilance while in operation as the sprayable formulations must have played a significant part in their acceptance by the end users. ?
Whatever form of pheromone technology that is used, it is inevitably a compromise between functionality and cost. A product based on a large amount of high quality pheromone in a hi-tech, high-priced formulation may be the best solution for a particular pest problem, but who will buy it? Investment in new product development in this field has to be directed towards economical solutions.
Commercial considerations
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With a few notable exceptions, for the most part the companies involved in pheromone development have either been small start-up companies or largely independent subsidiaries of larger companies. Often in these organisation there has been a youthful and enthusiastic research team keen to see this technology developed. More often than not, the focus has been very technically driven, and not enough thought has been given to basic commercial considerations which are the key to successful exploitation of any new technology.
Factors which can cause problems in commercialisation of mating disruption technology:
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(1) Poor assessment of the economic viability of products for target pests in target crops. (2) Inaccurate and/or over-optimistic cost projections for the product when manufactured on a large scale. (3) Over-expectations of the likely acceptance of this new technology by customers. Our experience has shown that they are not willing to pay more for a system that may be more difficult to use and sometimes offers less performance or security compared to conventional technologies. (4) Poor planning of research and development strategy whereby resources are often wasted on non-productive trials.
Factors which lead to the successful commercialisation of mating disruption technology:
(1) Accurate assessment of the commercial potential for a product (What is the market? How will it be used? How will it be integrated with other pest control practices? What would motivate the farmers to use it? (2) Product with good efficacy and predictable reliability; sound technical support data is required to back-up the product introduction into the market. (3) Development of an economic formulation and synthesis route which is easy to produce and scale up as demand increases. While conforming to efficacy requirements, the formulation must be easy, quick and economic to produce, particularly if the product is to be produced in large volume. (4) Both public and private support for a co-ordinated implementation programme. Area-wide treatments co-ordinated by public organisations or growers' associations have consistently given good results in crops such as cotton (Jones 1994), rice (Casagrande 1993) and top fruit (Dunley 1996). (5) Well organised distribution plan and pricing policy. Knowledge of how the product is to be sold and the price structure to the end user is essential. Everyone in the supply chain has to be motivated if the technology is to be successfully introduced to the farmer.
Future directions
Continuing Research
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Although as an industry we have learnt a great deal about the optimal conditions for successful mating disruption over the last decade (Neumann 1992, 1993; Kirsch & Lingren 1993) there is still a great deal that we have to learn. It is a significant concern for everyone involved in this field that funding from the public purse for research in this area seems to be diminishing, especially in view of the fact that the commercial use of pheromones is still growing.
There have been a number of interesting observations which have been made recently which deserve to be researched further:
(1) There is clear evidence from a number of sources that the continued use of mating disruption, where it is successfully controlling the target pest, leads to a gradual reduction in that pest over several seasons. In other words, there seems to be a "carry over" effect from one season to another as far as the population is concerned. Priority must be given to understanding how this process can be achieved in a majority of species especially if there is the concomitant possibility of reducing the amount of pheromone required for mating disruption as the population reduces.
(2) Work done in the USA is clearly showing that it is possible to reduce the starting population for a multi-voltine species such as the pink bollworm by treating the over-wintering pupae with entomopathogenic nematodes. Is this a technique which can be applied to other pest species?
(3) Area-wide programmes have been very successful but is this simply due to the elimination of problems related to ingress of mated females or are there more subtle reasons which deserve to be explored?
As the pheromone industry matures, it is in danger of attracting the attention of suppliers of products of dubious quality since the barriers to entry are not as onerous as they are for conventional insecticides. Consumers of pheromone products increasingly demand of their suppliers products which conform to certain specifications and quality standards; it is incumbent on the semiochemical industry to establish high levels of product specification, quality and performance so that barriers to entry are sufficiently high to exclude the amateur, or worse still, the unscrupulous operator. The pheromone industry is coming of age and standards need to be established to protect both the consumers and the credibility of the industry. The activities of the USDA-ARS and APHIS in establishing such standards for monitoring lures and traps have to be applauded (Leonhardt et al. 1990). However, it should be the industry itself that sets the standards and we have an unique opportunity to do this following the establishment of the International Biocontrol Manufacturers Association (IBMA) which has a semiochemical professional group and several other working groups to tackle areas such as registrations, specifications, etc., and which has the potential to give the industry the level of self-regulation that it clearly needs. The IBMA will also maintain a dialogue with the regulatory authorities worldwide in order to ensure that the process of product registrations continues to strike the right balance between a fair assessment of risk and facilitating the introduction of benign technologies.
The success that has been achieved to date has been based on partnership between the industrial semiochemical community, the publicly funded research and regulatory community, and end user groups and associations. Only through continued partnership of this nature will the technology go forward. Lindgren (1990) described the process as the "Research, Development and Application Continuum". We still have a great deal to do in order to secure the efficient operation of this process in the case of semiochemicals, especially in light of the fact that there are significant counter currents which are acting against us. These include reduced research and development funding from the public purse; pressure in both developed and developing markets for less government intervention in pest control activities i.e., privatisation of many pest management coordinating and implementation activities by government bodies; and lastly the rather feast or famine approach of financial investment communities towards the fledgling industrial companies trying to introduce pheromone technology to the field of insect pest management.
References
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