Incorporating insect infestation into rodent seed dispersal: better if the larva is still inside

Many nutritious seeds are commonly attacked by insects which feed on the seed reserves. However, studies have not fully explored the ecological implications of insect infestation in animal seed dispersal and subsequent plant regeneration. Our question is whether the fact that an infested seed still contains the larva or not might increase/decrease the probability of being successfully dispersed by animals. This study examines the effects of weevil-infested seeds on the natural regeneration of a rodent-dispersed oak species. Rodents showed a high ability to discriminate between sound and infested seeds, even when the larva was still inside. As a result, rodents caused differential seed dispersal for sound and infested seeds by modifying multiple aspects of the dispersal process. We found that, for the same seed weight, infested acorns with a larva still inside can contribute to natural regeneration (0.7 % of seedlings in next summer), although in comparison to sound acorns they suffered higher predation rates by rodents (both partial and complete), were removed later from the ground (less preferred), cached less frequently, and dispersed to shorter distances, which reduced their potential to colonize new environments. However, infested seeds with exit holes are notably less preferred by rodents and, when dispersed, they are mostly deposited on the litter (uncached) with shorter dispersal distances and lower emergence success. Thus, the probability that larval-holed acorns will produce viable seedlings is extremely low (null in this study). Whether infested seeds still contain a larva or not clearly determines the probability of being successfully dispersed. Premature seed drop prolongs the presence of the larva inside the acorn after seed drop, and could be a possible mechanism to allow dispersal of infested seeds.