Waterlogging increases the infestation level of the pest psyllid Creiis lituratus on Eucalyptus dunnii

The lerp-forming psyllid, Creiis lituratus Froggatt, is the most damaging pest of Eucalyptus dunnii Maiden plantations growing in north-eastern New South Wales. During the past 10 years there have been numerous reports that stands of E. dunnii planted on low-lying areas that were prone to waterlogging were also prone to infestation by C. lituratus. The objective of this shadehouse study was to determine whether C. lituratus prefers young E. dunnii exposed to intermittent waterlogging compared with other treatments (drought, normal watering and a control using normal watering plus an insecticide). Also we assessed whether the nutritional status of E. dunnii foliage, in particular amino acid content, differed between watering treatments. Field-collected C. lituratus adults were released into the shadehouse three months after establishing the watering treatments to individually-potted E. dunnii arranged in a 14 × 6 randomised design. Three months after release of the psyllids, we counted significantly more eggs and nymphs present on the plants subjected to intermittent waterlogging compared with the other treatments. Applying general linear modelling (GLM) and Akaike's information criterion (AIC) we found that the best model included both watering treatment and plant structure (through height and diameter), with psyllid infestation (eggs + nymphs) significantly higher on the waterlogged plants and significantly lower in the drought treatment compared with the normal watering treatment. The application of the generalised estimating equations technique to foliar content of individual amino acids and nutrients did not reveal a clear association with watering treatment or psyllid infestation. Most of the significant differences in amino acid content between treatments were between plants watered normally but with or without the systemic insecticide imidacloprid applied as a soil drench. No eggs or nymphal stages were recorded on the plants treated with imidacloprid. This trial demonstrated that the psyllid C. lituratus has a preference for young E. dunnii subjected to periodic waterlogging. Plantation growers can improve their site-species match for E. dunnii by avoiding sites prone to waterlogging.