Effect of host-tree and environmental variables on honeydew production by scale insects (Ultracoelostoma sp.) in a high elevation Nothofagus solandri:forest

Honeydew excreted by phloem-sap sucking scale insects (Ultracoelostoma sp.) living in the bark of beech (Nothofagus solandri:) trees growing at a high elevation (900 m) site in the Craigieburn range of Canterbury, New Zealand, was measured over four days during 1–10 May 1996. Average standing crop of honeydew sugar was 3.1 mg m-2, and ranged from 0.4 to 5.5 mg m-2. Daily production of honeydew sugar ranged from 0.2 to 1.5 mg insect-1 24 h-1, and 4.1 to 45.9 mg m-2 24 h-1. Honeydew production varied significantly between trees, and trees with the highest mean individual rates of production (mg sugar insect-1 24 h-1) tended to be those with the highest numbers of insects per unit bark area. Air temperature averaged over the 24 hours preceding each production sample explained 65% of the variability in 3-hourly honeydew production, showing that honeydew production is controlled by environmental and host-tree variables. Using this data, together with previously published estimates of carbon uptake and seasonal variability in honeydew standing crop, it was estimated that carbon contained in honeydew is equivalent to 1.8% of net primary production of beech trees at Craigieburn. Determining the effects of environmental variables on tree and insect physiology will allow formulation of an environmentally-driven process-based model of honeydew production.