Validation of a degree-day model for Listronotus maculicollis (Coleoptera: Curculionidae) development in New York golf courses

Field studies were conducted for two seasons to validate nonlinear degree-day models for cohort development of the annual bluegrass weevil, Listronotus maculicollis (Kirby), whose larvae cause severe damage to golf course turf in the Northeast. First and second instars reside and feed inside the host plant, and forth and fifth instars reside in the topsoil and feed on crowns. Third instars are the transitional stage and belong to both habitats because it is unknown when they move to new habitats. These five larval stages were divided into two groups, stem borers (first, second, and third instars) and crown feeders (third, forth and fifth instars), and the models were generated for both groups from the population data collected in upstate NY for three years prior to this validation study. The best model for each group was determined by using Akaike’s Information Criteria. It was tested at six golf courses in Upstate and Downstate NY. Population data were collected with a newly developed portable heat extraction system for soil cores. In 2008, the majority of data points of both stem borers and crown feeders fell off 95% prediction intervals during the mid-season. In 2009, on the other hand, the majority of the data points fell within the prediction intervals through the season. This diversion might attribute to occasional synchronous population development, which we did not observe during the model generation. The improvement and its applicability of the model are discussed.