Seasonal Occurrence, Phenological Indicators and Mortality Factors Affecting Five Scale Insect Species (Hemiptera:Diaspididae, Coccidae) in the Urban Landscape Setting

Abstract

Proper timing of pesticide applications is paramount when attempting to control scale insects (Hemiptera: Diaspididae, Coccidae) that are important pests of landscape plantings. Use of degree-days and phenological indicators can better time the applications and reduce the number of treatments. Seasonal appearance of five species of scale insects in the urban landscape along with flowering phenology of 40 plant species were systematically monitored during 1997, 1998, 1999 and 2000 in Athens, GA. Degree-day calculations for predicting first-generation crawler emergence were attained by two methods: use of standard-base or an experimentally determined base temperature. Predictions using a standard temperature resulted in high year-to-year variance. Use of a model-derived base temperature reduced the variance for degree-days needed for first crawler emergence. Mean base temperatures for European fruit lecanium, Indian wax scale, obscure scale, euonymus scale, and tea scale were, respectively, 12.78, 12.78, 5.0, 3.89, and 5.0°C. The range in degree-days required for first crawler emergence of each species using first the experimentally derived base, or the standard base temperature of 10.56 were 1184 to 1296 or 1064 to 1622 for European fruit lecanium; 846 to 1014 or 1150 to 1380 for Indian wax scale; 1246 to 1268 or 515 to 566 for obscure scale; 1366 to 1492 or 313 to 597 for euonymus scale; and 526 to 1502 or 202 to 776 for tea scale. Natural enemy complexes observed in association with each of the scale species are discussed.