Indonesia Workshop Explores
Bio-Control of Leucaena Psyllid

A Winrock International conference in Bogor Indonesia last January brought together scientists concerned with the invasion of the leucaena psyllid, Heteropsylla cubana, into Asia. The conference reaffirmed the severity of the current situation and reported on progress towards control of this pest of the developing world's most popular multi-purpose tree crop.

Leucaena psyllid is a sucking insect native to the area of Central America where the tree, Leucaena leucocephala, originated. Since the first sighting of the pest in Hawaii in 1984, the psyllid has spread over 3 million square miles, spanning the region between China and Australia. The psyllid's invasion, now reaching western India, is defoliating and, especially when followed by drought, killing leucaena plantings.

Regional Efforts Show Promise!

Early efforts to find a solution to the psyllid pest problem quickly eliminated the use of pesticides for their high cost. Research now focuses on two strategies: the development of resistant leucaena varieties; and the use of biological control agents. Several years of research directed by the Nitrogen Fixing Tree Association identified a substantially resistant hybrid of Leucaena leucocephala. Although a promising start, further research is needed before resistant trees can be made available for widespread re-planting.

Hunting for the Right Bug

Research into biological control has focussed on the use of natural enemies of the psyllid: predators, parasites and diseases, both from the pests original home in tropical America and from the regions infested by the exotic pest. Natural enemies from the psyllids original range are showing particular promise. A team of scientists at the International Institute of Biological Control of the Commonwealth Agricultural Bureaux (CAB) have collected and identified natural enemies of the psyllid in 14 Latin American and Caribbean countries, where psyllid populations are controlled naturally. They identified over 20 ladybird beetle predators of the psyllid, but no one ladybird species appeared to be consistently associated with, or effective against, the psyllid.

For example, when the psyllid first appeared in Hawaii, it provoked the growth of large populations of Curinus coeruleus, and Olla v-nigrum. These beetles were effective only after the psyllid population had already reached damaging levels. At the Winrock International conference Dr. Ida Nyoman Oka of Indonesia announced results of research to enhance the effect of Curinus. The mass production and release of the beetle in restricted areas of a tea estate controlled the psyllid population even at pre-damaging levels.

Two kinds of parasitic wasps from tropical America were found wherever the psyllid was present: a species of Psyllaephagus, and a species new to science; Tamarixia leucaenae. The more abundant Tamarixia may be a useful addition to a complex of natural enemies for controlling the psyllid in Asia.

Dr. George Funasaki of the Hawaiian Department of Agriculture announced at the Winrock International conference in Bogor that a Psyllaephagus wasp has reduced psyllid populations in Hawaii even in small incipient populations which the beetles do not find. Dr. Banpot Napompeth of Thailand's National Biological Control Research Centre, is directing efforts to establish this wasp in Asia.

Advantages of Wasps

As a more specific predator than the ladybirds, the wasps may not endanger other biological control efforts, or threaten food webs. A general psyllid predator such as Curinus could threaten the food supply of one of Australia's endangered species, the bell miner bird, which feeds exclusively on eucalyptus psyllids.

As Africa prepares itself for the appearance of the Leucaena psyllid, the International Centre for Research on Agroforestry, together with CAB International and other regional organizations, are establishing an early-warning system to detect the pest's first appearance on the continent. While it may not be possible to halt the spread of the pest into leucaena-based African alley cropping systems, continuing research on biological control and resistant species may eventually present solutions for Africa.

For more information, write to:

International Development Research Center for their
Sustainable Agriculture Newsletter, Vol 1 (2)
Tanglin P.O. Box 101
Singapore 9124
Republic of Singapore.