Leucaena is a leguminous tree from central America that is used in Australia as a high protein forage crop for beef cattle in tropical and sub-tropical areas. QDPI estimated the area ofleucaena as 4,000 ha in 1985, 30,000 ha in 1988, and suggested that 1.8 million ha may be planted by 1998 out of 6 million ha of suitable land. On average, cattle gain weight twice as fast on a leucaena pasture as on the next most productive Siratro pasture (R.M. Jones and R.A Bray, personel communication), four to eight times as fast on leucaena as on buffel grass (Elder, personal communication) and twice as fast as on black spear grass (Quirk et al., 1990). The leucaena psyllid, which sucks juices from leucaena leaves and stems, spread from its native central America to Hawaii in 1984 and to other Pacific islands,Australia, PNG, Indonesia and SE Asia by 1986.
Since then it has continued to extend its range westwards. In all the countries it has invaded, the psyllid has caused widespread defoliation and the death of some leucaena trees. In a short study at two sites, Palmer et al. (1989) found that the psyllid reduced growth by leucaena by 55%. A CAB study (Heydon and Alfonso, 1991) predicted cumulative losses in beef production due to psyllid damage to leucaena to be $121 million by 1998 at the then current rate of planting, plus major opportunity losses if the rate of planting should be reduced due to the psyllid.
The MRC commissioned the present CSIRO project to obtain more accurate assessments oflosses due to the psyllid. This project had research sites near Brisbane and Townsville, and a complementary QDPI project had sites near Rockhampton. QDPI will report separately on that project in which prolonged drought resulted in very low populations ofpsyllids, little growth by leucaena, and little useful information (Elder, personal communication).