In this section we welcome all your experiences in working directly with the end-users of arthropod and microbial biocontrol agents or in educational activities on natural enemies aimed at students, farmers, extension staff or policymakers.

Learning to Manage Leafminer Flies with Environment-Friendly Practices

The emergence of the potato leafminer (Liriomyza spp.) as a serious pest in the Cordillera Highlands of the Philippines highlighted farmers' needs for relevant and practical information on how to manage this pest. A Potato Leaf Miner Task Force (PLMTF) was set up in the Department of Agriculture - Regional Field Unit - Cordillera Administrative Region, and it has been researching the nature of the leafminer problem in the region, developing practical solutions, and pioneering methods for disseminating the information to farmers.

The first leafminer outbreak on potatoes in late 1999 led to damage on more than 1000 ha of crops in Benguet Province. Farmers repeatedly applied pesticide `cocktails', to no avail. Since then, four species have been identified from the region: the predominant species is L. huidobrensis, and L. trifolii, L. sativae and L. chinensis are also found. They have since been recorded infesting some 15 cultivated and ornamental plants.

Leafminers had previously been regarded as pests of minor importance. The increase in their pest status was attributed at least in part to the use of broad-spectrum insecticides against other pests (thrips, aphids and mites). This decimated the natural enemy fauna and precipitated the leafminer outbreaks.

The challenge was to show farmers that spraying against leafminers is not merely ineffective, but counterproductive, because the complex of natural enemies found in the Cordillera Highlands can, in combination with compatible management measures, provide far better control than pesticides. Surveys of leafminers in the region indicated that there was a complex of at least 10 parasitoid species that attacked them. A major hurdle that had to be overcome, however, was the small size of the parasitoids, which meant that farmers remained unaware of their existence and activity against the leafminer.

Over the last 3 years, the PLMTF has developed information packages for farmers, which they have made available both on a website* and on CD. The package comprises:

• `Primer on leafminers', which introduces farmers to what leafminers look like (including how to distinguish between species), reasons for their importance as pests, damage symptoms (on different crops and ornamentals), recorded host plants for each leafminer species in the Cordilleras, their life cycle, and options for leafminer management (see below).
• A video, `Knowing more about leafminers: their way of life and how to manage them'.
• A photo gallery of leafminers and their parasitoids, and leafminer damage.
• Three modules to provide training in (1) identification of leafminer flies and their natural enemies in the field using hand lenses, (2) collecting, preserving and shipping specimens, and (3) conserving natural enemies in the field for leafminer management.
• A parasitoid key: `Farmer's guide to identify natural enemies of leafminer'.
• Comics, which convey messages in a form farmers are familiar with; comics are a popular medium for public education in Southeast Asia.

The website and CD also include:

• Results of surveys in six provinces in the Cordillera in 2000-01.
• A database of some 125 leafminer-related published papers, as downloadable pdf files.
• An international directory of leafminer researchers - and a call for other researchers to make contact.

These knowledge-based materials and training materials were the product of the knowledge gaps identified when the PLMTF conducted a knowledge, attitude and practices (KAP) survey of the farmers in the leafminer outbreak areas. The print and audio-visual media were geared for non-specialists with resultant information for leafminer management made available in simple and easy-to-understand language/form.

The training created awareness about the importance of the leafminer natural enemies and ways to detect their presence in the farming world. In addition, it increased skills on the conservation of the natural enemies. The impact of the training and the knowledge-based materials became evident through a reduction in leafminer damage.

Learning about Leafminers

The identification training module shows users first where to find leafminer flies, and how to distinguish the flies from other insect groups they may encounter. It then introduces the four leafminer genera and shows how they differ, and looks at how infestations of the four Liriomyza species present in the region can be told apart - both from examining the adult flies and from the structure and location of the larval mines. Next, it introduces natural enemies, and explains in general terms how they can be distinguished from leafminers. This topic is expanded on in the parasitoid key, which also provides an illustrated guide to the natural enemies farmers are likely to encounter. The training module also explains how to tell whether natural enemies are present in a leafminer infestation.

The next module points out that one of the best ways to get acquainted with the different groups of insects is to go out and collect them. Rearing the immature stages to adults and handling and preparing them for preservation and storage provide experience that cannot be learned from textbooks. It describes where to look for the insects and the equipment and techniques needed for collecting, rearing, preserving and shipping them - and also how to record collecting data.

The last module describes different ways in which natural enemy populations may be encouraged and leafminers discouraged, and how to estimate levels of parasitism in their fields.

• Maintaining grass margins around fields provides a source of alternative hosts for natural enemies, and also pollen as food for adult parasitoids. In contrast, broad-leaved weeds should be removed as these can be alternative hosts for leafminers.
• Broad-spectrum insecticides should be eschewed. Insecticides should be selected and used with care, and avoiding early-season spraying allows natural enemy populations to build up.
• Natural enemy populations can be augmented by collecting infested material, rearing out the insects and releasing any adult parasitoids in the field.

Managing without Insecticides

The farmers' primer outlines management options that should be implemented at different stages of the crop cycle.

During planting, the emphasis is on firstly increasing pupal mortality through flooding, hoeing, exposing pupae to sunlight and practising agricultural hygiene and secondly minimizing leafminer infestation by using clean and/or resistant planting material, and removing any infested leaves that appear at an early stage.

The growing crop is more tolerant to leafminers if adequately watered. At this crop stage, monitoring and trapping are stressed. Sticky traps are advocated, both for monitoring adults moving in from surrounding crops and for mass trapping in the early phase of crop growth when the pest is at its most destructive. In general, this method has wide acceptance among farmers. Similarly, plastic trays placed under plants monitor and catch pupating larvae as they emerge from the leaves and drop to the ground. The real value of such traps on leafminer populations, damage reduction, beneficial arthropods and yields, and in detecting development of insecticide resistance is being evaluated.

A second strategy advocated at this stage is conservation of natural enemies. If parasitism approaches 50% or more, the chances of the leafminer population being kept below economic levels are excellent. Lastly, caution with nitrogenous fertilizers is suggested as they increase not only plant vigour but also leafminer larval survival and pupal size.

Harvest and post-harvest precautions centre on good sanitary and ploughing practices, and cold treatment of produce post-harvest. In addition, phytosanitary certification of produce can help prevent spread of leafminers between areas.

Specific advice to deal with outbreaks countenances integrating use of carefully selected chemicals with other IPM options. Given the widespread resistance of leafminers to organophosphate, carbamate and pyrethroid groups, and the toxicity of many insecticides to parasitoids, the options are limited. Farmers are advised to consider insect growth regulators (IGRs) and information on their use is given. Leafminer incidence decreased dramatically with their introduction and they are potentially compatible with natural control agents because of their low toxicity and host specificity.

What Next?

The PLMTF intend to come out with a revised version 2 of the leafminer CD, which will include the following new products and information:

• A simple video entitled `Killing action of natural enemies of leafminers'/`War against leafminers'. This will follow the simple extension philosophy of `seeing is believing'. It will use both film of natural enemies in action and animation to show farmers and extension agents the role of natural enemies.
• Email/contact addresses of leafminer researchers/scientists on a global scale. The aim is to initiate global networking between leafminer-interested individuals and stimulate discussion board-mediated sharing of knowledge and experiences, which will enhance exchange of information about leafminers and learning from the experiences of others.
• An updated information database of all published and unpublished information on leafminers.
• A village-level technology promotion programme for managing leafminers on vegetable and cut flowers using biocontrol approaches.
• A one-page `Leafminer flash: what's new' information exchange available as an email newsletter, to connect individuals interested in information on leafminer flies.

The team is keen to see this work, which was initiated to help farmers in one region of the Philippines, widened so farmers elsewhere can benefit. They call for appropriate international organizations to develop a mega-project to build on these initial efforts, perhaps under the umbrella of the CGIAR's SP-IPM (Systemwide Program on IPM).

*The PLMTF site is at:

www.bsu.edu.ph/leafminers/main.htm

However, power failures have meant significant interruptions in the service. In addition, the vast amount of information that needs to be made available on-line in the future will exceed the server's capacity. The PLMTF team is therefore pleased to say that the site is now co-hosted by Global Potato News at:

www.potatonews.com/leafminers/leafminers.asp

Contact: R.C. Joshi,
Crop Protection Specialist,
c/o Department of Agriculture,
Regional Field Unit,
Cordillera Administrative Region,
Baguio City, Philippines
Email: joshiraviph@yahoo.com or
rcjoshi@philrice.gov.ph or
joshiravi@hotmail.com
Fax: + 63 44 4560 112

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