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Management LMF

Control

Ecological and economical sound control of the leafminer fly is best realized when based on integrated pest management by promoting natural regulation and combining cultural practices with physical and chemical control.

1. Conserving beneficial insects. Leafminer flies are controlled by a large number of beneficial insects, which are either predators or parasitoids. The species involved depending on the agroecology where the leafminer flies. In regions rich in natural enemies it has been proven that leafminer flies are less damaging. Strategies to conserve beneficial insects can be manifold and include diversified cropping systems, high structural floristic diversity in agricultural landscapes, special weed management practices and the reduced use of selective insecticides.

2. Crop management. Healthy, vigorous growing potato plants are able to counteract the damaging effect of leafminers, particularly during the vegetative phase. The fast growing foliage enhances the egg extrusion reaction of the foliar tissue. Plants deficient in irrigation, water and fertilizer, or evolved from low quality seed (e.g. virus infested seed) show damage much earlier and mined leaves dry more rapidly. Under these circumstances, the negative effects of leafminer fly infestations further reduce low yields due to inadequate agronomic practices.

3. Adequate N-Fertilization. High N-content of leaves promotes leafminer fly development. Therefore, a balanced N fertilization should be considered.

4. Crop rotation. Continuous food availability by planting crop after crop will favor the abundance of the leafminer fly. It is therefore recommended to rotate with non-hosts.

5. Monitoring pest populations. Counting the number of flies captured in yellow sticky traps can monitor adult leaf miner flies. Counting the number of larvae or fresh tunnels per leaflet by sampling the bottom, middle, and top parts of the plant is used for monitoring larvae infestation. Both methods can be adapted for decision making to avoid unnecessary applications of insecticides.

6. Physical control. Yellow attracts leafminer fly adults. The use of mobile and stationary yellow sticky traps have been proved to effectively reduce leafminer fly adult populations thereby decreasing insecticide application costs by more than 50%.

7. Chemical control. Insecticides must be used only according to the monitoring results and when the leafminer population is expected to cause economic damage. By frequent sprayings leafminer flies have shown to become rapidly resistant to insecticides. Systemic insecticides with translaminar properties are most effective in controlling leafminer fly larvae. The products ciromazine, abamectine and spinosad can be recommended. Ciromazine has a residual effect of more than 20 days, followed by abamectina and spinosad. Abamectin is most specific with less negative effects on beneficial insects.

Prospect for Biological Control

Parasitoids play a very important role in the natural regulation of leafminer fly populations but are often suppressed by insecticide applications. In fields with insecticide spraying parasitisms is low compared to non-treated ones. In Peru, e.g., a complex of 17 larval parasitoids, with Halticoptera arduine, Chrysocharis flacilla, Diglyphus websteri and Chrysocharis caribea as the most abundant species, are involved in natural regulation. These observations stimulated worldwide biological control efforts and research and implementation largely focused on the use of inundative and inoculative biocontrol for open field and glasshouse conditions. Glasshouse applications have been mostly developed for horticultural industries in Western Europe and North America with Dacnusa sibirica, Opius pallipes and Diglyphus isaea as the most efficient parasitoids used. Classical biological control has been realized against L. trifolii and L. sativa with some notable achievements in vegetable production. Through the introduction and release of the Cucoilid, Ganaspidium utilis, in 1977 in Hawaii and in 1988 Tonga, both leafminer species are successfully controlled making chemical control unnecessary. On the other hand, the fungal insect pathogen Paecilomyces fumosoroseus is considered as a promising biocontrol agent. A natural mortality of 60% of leafminer fly adults was recorded in beans (Phaseolus vulgaris).