The smaller fruit tortrix, Grapholita lobarzewskii: predicting the phenology of adult emergence

The smaller fruit tortrix, Grapholita lobarzewskii Nowicki, has become a ma jor pest in the recent past in apple orchards north of the Alps. Neverthele ss little is known about the biology and the behaviour of this species. The effect of temperature on post-diapause development and survival was studie d under controlled conditions in order to establish a basis for the forecas ting of adult emergence. Survival was found to be highest at 17 degrees C a nd lowest at 11.8 degrees C. The sex ratio did not differ significantly fro m 1:1. Based on a linear relationship between temperature and developmental rates, thermal thresholds of 9.6 degrees C and 9.8 degrees C were determin ed for females and males respectively. The thermal constants, i.e., the mea n developmental times in physiological time units, were found to be 342 day -degrees for females and 317 day-degrees for males, suggesting a slight pro tandry. Based on the mean and the variance of the developmental times, a si mple temperature-driven phenology model was built using a time-varying dist ributed delay. The model was validated by visually comparing the prediction s with independent observations on adult emergence, and by calculating the temporal deviations of the predictions. In 4 out of 5 years the mean error was less than 3 days. The model was therefore found to give reliable foreca sts of the emergence of G. lobarzewskii and can be used to determine the op timal time for the exposure of pheromone traps, the application of pheromon e dispensers for mating disruption, and for the timing of insecticide appli cations.