Redbanded Leafroller (Lepidoptera: Tortricidae): Thermal Requirements for Development and Simulation of Within-Season Phenology in North Carolina

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Abstract
Developmental rates and survival of nondiapausing redbanded leafroller (RBLR), Argyrotaenia velutinana (Walker), eggs, larvae, and pupae were determined at eight constant temperatures: 5, 10, 15, 20, 25, 30, 32, and 35°C under a regime of 16:8 (L:D) photoperiod. Mean duration for each of five larval stadia by sex was determined at 25°C and protandry was shown. There was no survival at 5 and 35°C. Survival of eggs and larvae increased to 96.5 and 98.8%, respectively, at temperatures up to 20°C and fell at higher temperatures while pupal survival was highest at 25°C (92.1%). Temperature versus developmental-rate data were incorporated into linear and nonlinear models of temperature-dependent development to simulate adult emergence at variable temperatures. Lower developmental thresholds, degree day (DD) requirements, and percent of total developmental time for all stages individually and combined for six- (10, 15, 20, 25, 30, and 32°C) and four- (10, 15, 20, and 25°C) temperature linear models are given. Completion of one generation with the six-temperature linear model required 909 DD over a lower developmental threshold of 5.5°C, while the linear portion of the temperature-developmental rate relationship (four-temperature model) required 676 DD over 8.0°C. Parameters for a nonlinear model were established at all temperatures for each stage and for the combination of all stages. Simulations based on the nonlinear and the four-temperature linear model were validated by comparison with observed within-season male flight peaks using pheromone trap catch data from eight apple orchards. Linear models ran 0–4 d faster than nonlinear models. Of 18 actual flight peaks simulated, linear models simulated 11 and nonlinear models simulated nine within ±7 d of observed orchard flight peaks. Only one simulation predicted adult emergence early, all other inaccurate simulations predicted adult emergence 8–17 d late. Analysis of seasonal flight catch in each orchard and results of the model simulations suggest the presence of four generations of RBLR annually in North Carolina.