For insect species that produce multiple generations each year, there is varying levels of developmental synchrony that can manifest into cycles with either distinct, separate generations or overlapping generations where multiple life-stages are present. To understand this population-level phenomenon, it is crucial to explore the mechanisms that have been previously proposed such as the role of seasonal disturbances, like winter, in synchronizing development each year. Specifically, our aim was to explore how diapause, a period in which development is arrested at a specific-life stage, influences the developmental synchrony across a growing season. Our focal species was Cydia pomonella, a common tortricid moth pest with diverse intergenerational dynamics and which diapause as fully-grown larvae. We developed a physiologically-structured population model consisting of the insect’s life-stages (eggs, larvae, diapausing larvae, pupae, adults) and used distributed-delay equations to capture the variability in developmental periods. All vital rates such as development, survivorship, and fecundity were related to temperature with diapause induction and termination dependent on changes in photoperiod. All parameters were taken from previous laboratory works and the model was compared to pheromone trap data collected at the experimental farm site in Biglerville, PA.
Results/Conclusions
We found that the physiologically-structured model which incorporated diapause induction/termination better explained the dynamics of C. pomonella than models without. With temperature data from the experimental farm site, our model closely matched the timing of the two peak flights in the reproductive adults found in the pheromone trap data. The first flights which are comprised of the overwintering generation occur in mid-May and have distinct peaks while the second flights which peak around mid-July have a less synchronous emergence. This suggests that the induction of diapause in fully-grown larvae allows C. pomonella to both survive hazardous freezing temperatures and re-synchronize their development at the end of the growing season. In conclusion, incorporating diapause into stage structured models could provide further insight into the role of both the seasonal environment and life-history on the developmental synchrony across insect pest species.