Seasonal Occurrence and Development of Degree-Day Models for Predicting Activity of Conotrachelus nenuphar (Coleoptera: Curculionidae) in Alabama Peaches

The plum curculio, Conotrachelus nenuphar (Herbst) (Coleoptera: Curculionidae), is a key pest of peaches, Prunus persica (L.) Batsch, in North America. Captures of adult weevils in unbaited pyramid traps recorded annually from 2000 to 2008 in an unmanaged peach orchard in central Alabama were used to determine its seasonal occurrence and to develop predictive degree-day models. Spring migration of plum curculio began at bloom (early to mid-March). Linear, polynomial, and three-parameter Weibull functions were tested to describe the relationship between weekly trap capture and cumulative degree-day (DD). Criteria used to select the best models were the smallest Akaike information criterion and highest R2 values. A sixth-order polynomial function fitted best to seasonal trap captures and cumulative DDs and revealed two major seasonal peaks with the first (spring generation) and second (summer generation) peaks occurring at cumulative DDs of [approximately equal]245 and 1105 (base 10[degree]C, biofix of 1 January), respectively. A potential third (late summer generation) peak was observed at 1758 DDs. The sixth-order polynomial model predicted the first trap capture to occur at cumulative DD of [approximately equal]99 (base 10[degree]C, biofix of 1 January). The three-parameter Weibull model predicted the first trap and first peak (spring generation) trap captures to occur at mean cumulative DDs of 108.02 [plus or minus] 9 and 220.07 [plus or minus] 16, respectively. Validation of the models in the unmanaged orchard in 2009 and 2010 and in a second unmanaged orchard (located 1.6 km from the first) in 2009 showed that the polynomial and Weibull were within [plus or minus]7 d in their predictions of the first and peak trap captures of the spring population. Validation results showed that both models successfully predicted the first trap capture in one out of three scenarios and the peak trap capture in two out of three scenarios. The performance of the models is discussed in relation to management of plum curculio in central Alabama.