El Niño and the locusts

I arrived in Indonesia for the first time in June 1998. Major riots in the capital had just ended and the flight making the connection between Singapore and Jakarta was almost empty. The Indonesian authorities had asked the CIRAD expertise to help them cope with a serious locust invasion (Locusta migratoria Linnaeus, 1758). Significant outbreaks were reported in many islands of the Indonesian archipelago during the 1997-1998 rainy season, especially in southern Sumatra, but also Java, Kalimantan (Borneo), Sumba, Timor, Sulawesi (Celebes ) and Flores. The situation seemed serious and completely new for Indonesia who had no experience of a plague of locusts. These outbreaks were all the more surprising as the migratory locust lives mostly in drier areas (for instance in Africa) where rainfall doesn't exceed 1000 mm per year. Here it was 3000 or 4000 mm! What could possibly have caused this plague of locust? It was a mystery!

In Indonesia, during my first visit. Sukirno, the local engineer who asked for my expertise on locust problems is in the middle of the photo. The other people are local engineers and technicians from agriculture and plant protection services.

Locusta migratoria Linné adults, last nymphal instar (5th) (gregarious phase). Swarm of Migratory locust and damage on sucar cane. Recently deforested area on Borneo and creation of suitable places for the Migratory locust.

After a field survey in Java, Sumatra, Borneo, in areas of sugar cane plantations, of oil palm, in areas of subsistence rice farming, in zones of more or less recent deforestation... I realized that the first signs of this invasion had taken place in the recent past. But these phenomena were minor and remained unnoticed. Small outbreaks had occurred in 1992 and in 1995 ... before the very huge outbreaks of 1998. And each time, these outbreaks have coincided a few months before with a drought event connected to the famous El Niño phenomenon. A particularly strong episode occurred in 1997–98, resulting in drier conditions in various parts of Southeast Asia, and especialy Indonesia.

Collect of locust (nymphs) with large nets. Insecticide spraying (with products and technics most often unsuited). Swarm and damage on suger cane. Cassava cake studded with young larvae of locusts.

In fact, on the long-term, intensive deforestation that prevailed in Indonesia for many years had created many favorable environments where the Migratory locust could settle and develop. Then, each drought event linked to El Niño caused a significant reduction of natural enemies of this locusts, resulting in a locust population increase. The population became more important at each dry period... until the last and most important El Niño event of 1997, resulting in this massive invasion of 1998. The mystery was solved.

Over the next 3 years, I continued to visit Indonesia to support local authorities in the control of this locust invasion, in particular by providing training courses on the ecology of this insect as well as on the technical control practices, and by building an action plan for the long term.

Lecoq M., Sukirno, 1999. Drought and exceptional outbreak of the oriental migratory locust in Indonesia. Journal of Orthoptera Research 8 : 153-161.

Collect of locust (nymphs) with a large nets (left) and burial in pits (right).

Nota bene: There is only now two recognized subspecies: Locusta migratoria migratorioides (Reiche & Fairmaire, 1849) in tropical areas, and Locusta migratoria migratoria (Linnaeus, 1758) in temperate zones. Locusta migratoria manilensis (Meyen, 1835) is now a synonym of L. m. migratorioides (Reiche & Fairmaire, 1849).