Primer on Leafminers in Cordillera Administrative Region, Philippines

Foreword, Authors and Acknowledgements

Introduction

Species

Characteristics and Sudden Prominence

Nature of Damage

Host Plants

Life Cycle

Management Options

Management Options

A. During planting time 

Flooding the soil followed by hoeing could release mulch of buried pupae. Collect and destroy the pupae or expose to sunlight for desiccation and enhance other mortality factors. These prevent further increase of LM fly population. 
Maintain general agricultural hygiene conditions by cleaning all weeds and treating soils where practical to destroy the pupae. Bury infested weeds and waste plant materials in the ground. These can also be sealed with plastic film for over a month or burned but not composted. 
Plant insect-free propagating materials to prevent the introduction and spread of LMs. Carefully examine all propagating materials (except seeds) for LM infestation before planting. Handpick and destroy mined leaves. 
Plant resistant/tolerant cultivars to reduce damage and yield loss by LMs. In potato, the resistance is ascribe to the high density of glandular trichomes (hair-like structures) which physically reduce feeding and restrict oviposition sites. Other resistance mechanisms include: hypertropic growth of the leaf tissue surrounding the incrusted eggs (so that eggs are exposed to desiccation and predatory action); hypersensitivity, in which eggs are surrounded by necrotic tissue so that the newly hatched larvae cannot survive; leaf tolerance of mining damage, in which the leaf remains moist, whereas it dries out in a susceptible plant. 

B. With standing crop

Plants that are not stressed for moisture can better tolerate to this pest. 
Use 3-by-5 inch yellow sticky cards to monitor adults moving into the fields from surrounding crops being harvested. They are also used to mass trap LM adult flies. This technique reduces the rate of increase of the pest as it attracts, catches and kills the LM adults in the early phases of the plant’s growth, when they are most destructive. In general, this method has wide acceptance among farmers. The real value of such traps on LM population, damage reduction, beneficial arthropods, detects development of insecticide resistance, and yields are being evaluated. 
Use plastic trays to monitor pupating larvae emerging from the leaves. Place trays under plant to catch the larvae as they drop to the ground. 
Conserve natural enemies. Beneficial organisms naturally abound in the field and are important regulators of LMs as they periodically suppress LM populations. In the absence of pesticide applications, LMs are parasitized by numerous beneficial organisms (insect parasitoids and predators, entomogenous fungus, and nematodes)non various crops. If parasitism approaches 50% or more, the chances of the LM population being kept below economic levels are excellent. 
Avoid using higher nitrogenous fertilizer levels. Higher fertilizer regimes increase overall plant vigor (height and leaf area), larval survival, and size of pupae. 

C. During/after crop harvest

Never leave plant materials after harvest. Clean and burn all infested plant debris to impede the LM populations. 
Deep plowing after harvesting crop aid greatly in reducing LM numbers. 
Phytosanitary certificate should be required for cut flowers, for harvested and transported vegetables with leaves to prevent its spread in uninfested areas. LM adult flies are capable of limited flight. However, the dispersal over long distances is on planting materials of host species and cut flowers. 
Expose cuttings of ornamental plants/leafy vegetables to 0oC for 1-2 weeks in cold storage kills all LM stages. 

D. During outbreaks

Integrated chemical control with other IPM options. LMs are notoriously difficult to control with the use of insecticides alone, as they are resistant to many conventional insecticides belonging to organo phosphate, carbamate, and pyrethroid groups. Deltamethrin is effective against adult flies, but is highly toxic t parasitoids. Methomyl disrupt parasitoids of LMs and induce LM outbreaks. The most effective insecticides to control the larval stages must possess systematic and translaminar properties. 
In response to the loss of effectiveness of many agricultural chemicals, the insect growth regulators (IGRs) such as cyromazine, abamectin, and avermectin were introduced for LM management. The incidence of LM decreased dramatically with the introduction of IGRs. However, these insecticide products have limited crop registration and must not be used on unregistered crops. IGRs are potentially compatible with natural control agents because of their low toxicity and host specificity. 
The properties of some of the agrochemicals used for LM management are as follows: 

Abamectin is an insecticide and acaricide with contact and stomach action. It reduces the rate of complete egg hatch. Its residues induce mortality of both sexes of LMs, especially females, and reduce oviposition and feeding by females. Furthermore, the abamectin residues do not act as repellent. Thus, LMs exposed to treated leaves and the effects on mortality; feeding and oviposition is expected to be manifested in some extent if foliar sprays were not uniform. Entomopathogenic nematodes (Steinernema feltiae and Heterorhabditis megidis) can control LMs successfully and can be used in conjunction with IGRs such as abamectin provided high humidity is maintained. However, abamectin is highly toxic to honey bees. 

Avermectin suppresses LMs but does not adversely affect seasonal per cent parasitism, adult parasite mortality, and survival and emergence of immature parasitoids from treated foliage. 

Cyromazine has a contact action that interferes with molting and population. It is a larvicide, which could be applied to coincide with either adult or larval activity. It lacks adulticidal activity and repellent effect on feeding and oviposition. Thus, development and resistance towards it would be slow, as it does not deter oviposition puncturing by LMs. However, cyromazine significantly reduces relative abundance of some key parasitoids of LMs and seasonal parasitism.