A degree-day model to predict population dynamics of the cranberry fruitworm, Acrobasis vaccinii Riley (Lepidoptera: Pyralidae), in highbush blueberries

A temperature-based model was developed to predict the emergence of adult male cranberry fruitworm, Acrobasis vaccinii Riley (CBFW) from overwintering sites and the beginning of oviposition by females in highbush blueberry. From 2003 to 2007 information on the population dynamics of CBFW was collected at eight different farm sites in West Michigan. The relationship between cumulative percentages of both male moth captures in pheromone traps and oviposition and daily Growing Degree Day (GDD) accumulation was described using a three-parameter Weibull function. The three-parameter distribution allows for the introduction of a biofix value to start the calculation of the distribution. The resulting model was: f(x)=1- exp[-((â-á)/ã)ç], where f(x)=cumulative CBFW at T(t), â=cumulated GDD at T(t), and á=biofix. The parameters ã and ç are scale and shape parameters of the Weibull distribution. In 2007, we validated the model at eight blueberry farms, and cumulative adult emergence and oviposition percentages were compared with the model’s predictions. For the adult population the resulting model was Y=1- exp ((CumGDD-Biofix)/422.02)^2.97, where biofix=374±30 GDD (base 50°F). For egg-laying the model was: Y=1-exp((CumGDD-Biofix)/394)^2.224, where biofix=463±10 GDD (Base 50°F). In both cases, once biofix was set, the Weibull function accurately predicted the emergence of males and oviposition by CBFW. A t-test showed no statistical difference between observed and predicted emergence curves. This model provides a reliable predictive tool for CBFW phenology, but its accuracy and utility will depend on precise weather data collected at the monitoring site.