Predator avoidance through enemy-free space (EFS) can potentially explain the diverse patterns of host plant use that are observed in herbivorous insects. Predation differences between suitable host species are usually attributed to plant chemical and/or morphological traits alone, whereas the effect of spatial variation in predator abundance is rarely considered. The present study investigates the effect of spatial heterogeneity on EFS in a leafminer, Amauromyza flavifrons (Agromyzidae). To identify effects of spatial heterogeneity, rates of mortality due to parasitoids were estimated when host species were growing in distinct patches (as occurs in nature) and when they were interspersed (the common garden experiment).
Results/Conclusions
Under both conditions, the leafminer suffered higher parasitism when feeding on Saponaria officinalis, a permanent host, than on Silene latifolia, an ephemeral host. However, the mortality difference was greater in the between-patch comparison than that observed in the common garden experiment. Levels of parasitism were also density dependent in patches, suggesting that spatial heterogeneity in parasitoid load could amplify the fitness benefit of EFS. The results indicate that EFS can have strong fitness consequences for herbivorous insects, and that such consequences are only evident when EFS is examined in a spatial context. Spatial heterogeneity may be particularly important when the “enemy-free” host is ephemeral and thereby prevents the accumulation of parasitoid populations. This EFS advantage might explain why the leafminer use ephemeral resources in temporally and spatially heterogeneous environments.