Deforestation, drought and exeptional outbreaks of the oriental migratory locust, Locusta migratoria manilensis (Meyn 1835) in Indonesia

Serious outbreaks of oriental migratory locusts, Locusta migratoria manilensis, have been reported on different islands of the Indonesian archipelago during the rainy seasons 1997-98 and 1998-99. Sumatra, Java, Kalimantan, Sumba, Timor, Sulawesi and Flores were particularly affected. By far the most serious outbreaks were recorded in southern Sumatra, in Lampung province, in 1998. Such large outbreaks seems a new phenomenon. They were much larger than the small local upsurges recorded in the past. On the long term prospect these outbreaks are certainly caused by drastic environmental changes. The intensive deforestation that has been under way over the last 20 years is certainly partially responsible for these, outbreaks. In many places, the natural forest has been replaced by large plantations: sugarcane, oil palm, natural rubber, cassava, etc. New biotopes were created, sonic of which seem to be very suitable for migratory locusts, c-specially in sugarcane, plantations on light soils. These areas are certainly source areas (at least pail of them) of the recent outbreaks, specially in Sumatra. On the short term, the drought that Prevailed in Indonesia in 1997 also seems to be a major recent factor that prompted these outbreaks. Meteorological data analysis indicate that these outbreaks are likely to be linked to the frequency of droughts which prevailed more often in these areas during the last ten years, as the famous 1997 El Niño drought. We have indications that the problem might become recurrent in Indonesia and grow even worse in the future. (Résumé d'auteur