DEVELOPING DAY-DEGREE MODELS TO PREDICT SPREAD WITHIN CALIFORNIA OF GONATOCERUS TRIGUTTATUS RELEASED FOR GLASSY-WINGED SHARPSHOOTER CONTROL, AND USING DEMOGRAPHIC DATA TO INVESTIGATE PARASITOID SPREAD IN CALIFORNIA

• Author(s): Hoddle, Mark; Pilkington, Leigh;
• Abstract: The reproductive and developmental biology of Gonatocerus triguttatus Girault, a parasitoid of the glassy-winged sharpshooter (GWSS; Homalodisca vitripennis; formerly H. coagulata), was determined at five constant temperatures in the laboratory; 15; 20; 25; 30; and 33C. At 25C, G. triguttatus maintained the highest successful parasitism rates with 25.1% of parasitoid larvae surviving to adulthood and lowest parasitism was observed at 15C with 7.3% of parasitoid larvae surviving to adulthood. Lifetime fecundity was greatest at 25C and fell sharply as temperature either increased or decreased around 25C. Temperature had no effect on sex ratio of parasitoid offspring. Mean adult longevity was inversely related to temperature with a maximum of 20.6 days at 15C to a minimum of four days at 33C. Developmental rates increased nonlinearly with increasing temperatures. Developmental rate data was fitted with the modified Logan model for oviposition to adult development times across each of the five experimental temperatures. Optimal, lower, and upper lethal, temperature thresholds for G. triguttatus were, 30.7C, 10.4C and 38.8C, respectively. The lower developmental threshold estimated with linear regression was 10.57C, and is very close to the lower temperature threshold estimated by the modified Logan model. Linear regression of developmental rate across all five experimental temperatures indicated that 204 degree-days were required above the minimum threshold of 10.57C to complete development. Demographic parameters were calculated and (pseudo replicates for intrinsic rate of increase (r)m(), net reproductive rates (R)o(), generation time (T)c(), population doubling time (T)d(), and finite rate of increase ( ) were generated using the bootstrap method. Mean bootstrap estimates of demographic) parameters were compared across temperatures using ANOVA and nonlinear regression.
• Publication Date: Nov 2006
• Journal: 2006 Pierce's Disease Research Symposium