Flowering phenology and seed predation by a tephritid fly: Escape of seeds in time and space

Seed predators, like pollinators, may potentially act as a selective force on flowering phenology. Attack patterns by the specialist tephritid fly Paroxyna plantaginis (Diptera) were studied at the northern distribution limit of its monocarpic host plant Tripolium vulgare (Asteraceae). which is characterized by an extended flowering period. Plants were successfully transplanted onto eight islands and removed successively throughout the season in order to follow the temporal and spatial variation in attack risk. The results were compared to patterns found in eleven natural populations. Early (terminal) Flower heads had higher potential seed set and were less prone to attack by P. plantaginis in a year with normal high attack rates and under normal weather conditions. The attack to terminal flower heads followed the overall attack risk at the plant level. The density of ovipositing females early in the season was the most likely explanation for the attack pattern. This suggests a phenological lag between thr first flowering heads and the emergence of seed predators, which may break down at high fly densities. Spatial and stochastic factors affected fly density, which may confuse the selective force.