An episodic model of honeydew production in scale insects



Honeydew produced by sooty beech scale insects (Ultracoelostoma spp., Homoptera: Coelostomidiidae) is a keystone ecological process in New Zealand beech (Nothofagus spp., Nothofagaceae) forest. This work puts forward a model of honeydew production based on individual insects that presumes feeding and excretion are episodic processes driven by the insect rather than the passive processes that were previously assumed. The model is parameterized using existing data and then compared to an independent pre-existing dataset. The model suggests that over a 12-h period, on average the insects suck sap for 2 h, and excrete waste sap for 12 min. Resource uptake by the insects appears to be limited by the time required to process the sap, consistent with the observed relationship between honeydew production rates and ambient temperature. This implies that insect feeding rates may be ultimately limited by the low nitrogen content of phloem sap.