Total annual seed loss on a perennial legume through predation by insects: The importance of within‐season seed and seed feeder dynamics

Abstract

Abstract Determining total annual seed loss from seed predators is an important step in quantifying the role they have in modifying plant populations. Total seed loss is typically estimated with a single, well‐timed survey. However, this overlooks the potential importance of within‐season patterns of seed availability and insect activity, particularly where seed gain and loss are not synchronous and where insects are multivoltine. In Australia the introduced legume weed, Parkinsonia aculeata L. (Caesalpinaceae) is one such example. A replicated survey was conducted throughout a single cropping season in two contrasting habitats (uplands and wetland) to estimate total annual seed loss from seed predation and to test the relative importance of seed availability, seed feeder abundance, seed feeder behaviour and parasitism in determining total seed loss. Two seed feeders were present, the introduced biological control agent Penthobruchus germaini (Pic) (Bruchidae) and the moth, Mesophleps palpigera (Walsingham) (Gelechiidae). Seed availability patterns differed with habitat, with a greater proportion of seeds being available for longer in uplands, and resulted in total seed consumption by the beetle being twice as high in the uplands (5.2%) and no difference between habitats for the moth. Total seed loss from beetle predation was restricted by the egg parasitoid Uscana sp. (Trichogrammatidae), which was abundant throughout the season, and also by unexplained larval mortalities. This study highlights the potential importance of within‐season interactions between plant, seed feeder, natural enemies and environment in determining total seed loss through predation. The possible population and evolutionary consequences of such interactions for both the plant and the seed feeder require further consideration.