L. huidobrensis, also known as potato leafminer in Indonesia, has spread rapidly around the world in the last 10 years. It is an important pest in Europe, Israel, Sri Lanka, Philippines and South Africa, and now in Indonesia. It has become a major problem is potatoes and many other vegetable and flower crops in Java and Sumatra and has spread into Sulawesi and Bali.
Indonesian farmers have struggled to control the pests despite using many applications of insecticides. In potatoes yield losses of 30 to 70 per cent have been common. Many crops are receiving twice-weekly sprays, leading to a rising incidence of insecticide resistance. Natural enemies such as parasitoids are also affected by the sprays.
The Victorian-Indonesian vegetable industry development project convened a meeting of 12 Indonesian scientists and integrated pest management trainers in June 2000. Determination of effective biological control of L. huidobrensis and extension of the strategies to farmers were identified as the highest priorities for collaborative research.
To date none of the polyphagus Liriomyza species has colonised Australia. However, in view of their recent colonisation of Indonesia and their spread in the South Pacific, their arrival seems imminent. Major vegetable and ornamental crops at risk include potato, celery, tomato, onion, brassicas, chrysanthemum and gerbera. The Australian vegetable industry is worth around $1.8 billion.
The primary objective of this project was to increase the sustainability of vegetable production in Indonesia by reducing the impact of the pea leafminer Liriomyza huidobrensis on vegetable crops. Researchers aimed to reduce the use of insecticides by using non-chemical control methods, including the use of parasitoids, and thus retard the development of insecticide resistance in L. huidobrensis.
A secondary objective was to increase the preparedness of Australian horticultural industries for the arrival of L. huidobrensis or related Liriomyza species in Australia.
Trials of insecticide-free crops of potatoes were undertaken in West Sumatra and South Sulawesi. The population dynamics of L. huidobrensis and its natural enemies were studied and comparisons made with farmers crops grown nearby. Further detailed surveys of potato and other vegetable crops were undertaken in eastern areas of Indonesia affected by Liriomyza spp. In Australia, the parasitoid fauna of Liriomyza spp. were documented through museum records and field collections of related leafminer species.
Researchers studied the impact of insecticides and fungicides on the parasitoids of leafminers (both endemic and exotic) and designed trials to select for insecticide resistance in key parasitoids in both Indonesia and Australia.
Indonesian scientists received training in techniques for managing insecticide resistance in Liriomyza spp. and other agricultural pests. The research team sought to develop resistance management programs for abamectin and cyromazine, the most effective insecticides in use.
The project highlighted the importance of local parasitoids and other beneficial insects in controlling pest leafminers, and developed diagnostic keys using Lucid software to identify both the parasitoids and the leafminers.
Analysis of the comprehensive survey data on the distribution of leafminers and their parasitoids in vegetable crops in West Java, North Sulawesi, South Sulawesi and Bali showed that L. huidobrensis is mainly found over 1000 m above sea level (asl), whereas L. sativae, the vegetable leafminer, is generally restricted under 700 m asl. The scientists found very little overlap between the two species. The project team showed that L. sativae had become well established in lowland areas in Indonesia, where it was a major pest of beans, tomatoes and cucumber. Both flies continue to spread eastward through Indonesia.
Since its discovery in 2000, Liriomyza chinensis, onion leafminer, has continued to spread through lowland areas of West and Central Java, where it is damaging shallots. In 2003, project scientists detected it in some highland areas of West Java. Another two leafminer species were identified for the first time in Indonesia. The project used PCR-RFLP techniques (a form of DNA fingerprinting) that enabled them to distinguish between Liriomyza species and develop species-specific profiles to separate those of high quarantine significance to Australia (L. huidobrensis, L. sativae and L. trifolii) from a range of less important species that share one or more hosts (L. brassicae, L. chinensis, L. yasumatsui, L. katoi and L. chenopodii). None of these important Liriomyza species have yet been recorded in Australia.
The project scientists did not develop or test any practical and effective integrated pest management (IPM) solution or strategy for farmers to use to control leaf miners and reduce pesticide usage. However they gathered comprehensive data on the distribution and impact of leafminers and their parasitoids in vegetable crops in Indonesia, which could also be useful for Australia. They identified 19 species of leafminer parasitoid from the surveys in Indonesia and 15 from samples collected in Victoria. The project team concluded that it was unlikely that foreign importation of parasitoids would be required for Indonesia or, in the case of an incursion of polyphagous Liriomyza spp., for Australia.
The project team undertook detailed studies of the population dynamics of L. huidobrensis on unsprayed and sprayed commercial potato crops in West Sumatra (four cropping seasons) and South Sulawesi (four cropping seasons). In each location, the use of insecticides generally had little impact on suppressing the leafminer population and also often reduced the level of parasitism.
Bioassay data for the insecticides abamectin, cyromazine and dimehypo (a nereistoxin analogue insecticide used widely in Indonesia) showed all three chemicals were effective against larvae of three Indonesian populations of L. huidobrensis with different histories of chemical exposure. But dimehypo and to a lesser extent abamectin were harmful to parasitoids. These results suggest that, in Indonesia, cyromazine can be incorporated into Liriomyza control programs that conserve parasitoids, whereas dimehypo and abamectin need to be used cautiously. Repeated applications of profenofos were ineffective in controlling L. huidobrensis numbers on potatoes in the field but reduced parasitism and predation. These detrimental effects may be responsible for the increased damage and decreased yield in the pesticide-treated fields.
These results highlighted the dangers associated with uncontrolled and indiscriminate use of hard chemicals for controlling leafminers, and the benefits of correct species identification in devising control strategies. Thus the scientists established the grounds for effective control strategies that can be implemented against leafminer in Indonesia.
The project also provided essential information for responding to potential leafminer incursions into Australia. There will also be associated benefits for other Pacific countries, which as yet have not recorded L. huidobrensis but do have other Liriomyza species present. The project work has successfully contributed to the training of graduate students in Indonesia and the development of strong links between Indonesian and Australian scientists.
Links:
[1] http://www.aciar.gov.au/country/Indonesia
[2] http://www.aciar.gov.au/programarea/Crop Protection