Psyllid resistance in Leucaena. Part 2. Quantification of production losses from psyllid damage

Abstract

The psyllid insect (Heteropsylla cubana) is known to reduce biomass production in Leucaena species, but little information is available on the level of reduction, or whether a commonly used plant damage rating scale can be related to production losses. Biomass production losses due to predation by the psyllid were determined for 12 accessions of Leucaena in a randomised split-plot field experiment conducted at Brisbane, Australia. Regrowth from well-established Leucaena trees, cut back to bare stems 50 cm high, was measured over a 9-week period from plants subjected to psyllid damage and from plants with psyllids controlled by spraying with chlorpyrifos (1 mg ai/l water). Psyllid damage was scored using a ratings scale developed by the University of Hawaii. Loss of potential DM production due to psyllids ranged from 10% for L. trichandra OFI53/88 to 76% for L. collinsii ssp. zacapana OFI56/88. Production losses were significantly correlated with psyllid damage ratings for 10 of the 12 accessions, and also for a combined data set comprising these 10 accessions. From correlations for the combined data set, a 50% loss of potential DM production occurred at a psyllid damage rating of approximately 3.2. Results indicated that a "0" rating should be added to the scale to indicate the absence of psyllids.