The effect of herbivore density on host plant mediated interactions between two insects

Recent work suggests that foliar‐ and root‐feeding insects can interact in a novel plus‐minus fashion. However, the effects of herbivores may be different at different densities. This paper describes two laboratory experiments investigating the effect of increasing insect density on plant performance and the host‐plant mediated interaction between a leaf‐mining fly and root‐feeding chafer larvae. Above‐ and below‐ground insect herbivory decreased plant performance. The effects of the root feeder were, for some parameters, different between the two densities of chafer larvae. Leaf mining significantly decreased the performance of the chafer larvae, while root herbivory was found to increase the pupal weight (related to fecundity) of the leaf miner. The effects of root herbivory suggest that the relationships between herbivore density and plant performance may be curved as the greater chafer density had no significant increased effect on the plants or foliar‐feeding insects.