A multi-Gaussian model for predicting crawler occurrence of Unaspis yanonensis in citrus orchards

Abstract

Arrowhead scale, Unaspis yanonensis (Kuwana) (Hemiptera: Diaspididae), feeds on the foliage, stems, and fruits of citrus trees and causes tree dieback when heavy infestations occur. Multi-Gaussian models (three- and two-peak models) were developed for better management of the arrowhead scale in citrus orchards and later validated against several field data sets. The oviposition activities observed in the laboratory were highly correlated with both models (r2 = 0.88). The three peak oviposition times estimated by the three-peak model were at 282, 500, and 694 degree-days, based on a low threshold temperature of 13 °C. Also, the peak oviposition times of the two-peak model were identical to the first and second peak times of the three-peak model. Both models accurately predicted the first oviposition peak period of field populations. In the later peak period, both model outputs well predicted the actual crawler populations, except for the tail end of actual peak periods which were underestimated in the two-peak model and overestimated in the three-peak model. Overall, both models showed a strong robustness for correlation with actual data. The newly developed multi-Gaussian models better described the actual population phenology of U. yanonensis than the previously published models, and either model would be useful for the management of U. yanonensis in the field. © 2010 The Authors. Journal compilation © 2010 The Netherlands Entomological Society.