Belowground herbivory influences plant growth and plant-pollinator interactions

Belowground herbivory is known to often have a negative effect on aboveground plant growth, fitness and interactions with other organisms. However, here we demonstrate for two different plant-insect systems in different climatic regions that belowground herbivory can also have positive effects on both, plant growth and interactions with mutualists such as pollinators. Potato plants (Solanum tuberosum) subjected to the feeding of Guatemalan tuber moth larvae(Tecia solanivora)  in Colombia produced tubers that were twice as large as those on control plants without belowground herbivory. Similarly we demonstrate that wild mustard plants (Sinapis arvensis), native to temperate regions of Eurasia and under attack by 1 to 11 root feeding click beetle larvae (Agriotes sp.) were not compromised in plant growth and had similar fitness as control plants without root damage. Interestingly, intermediate levels of root herbivory (3 click beetle larvae per plant) increased the attractiveness of those plants in comparison to control plants or to plants with a high density of root herbivores (> 8 click beetle larvae per plant) suggesting positive density-dependent fitness effects from root herbivory. Our results suggest that root herbivores may not always have a negative effect on plant development and/or on mutualistic interactions with other organisms. Possible underlying mechanisms of these effects are discussed.