Effects of earthworms on above- and belowground herbivores

Earthworms affect plant performance and can influence plant–herbivore interactions. Both primary and secondary metabolites and the expression of stress-responsive genes of plants can be affected by earthworms. Plant-mediated effects of earthworms on aboveground herbivore performance range between positive and negative. These indirect, plant-mediated effects likely depend on the altered resource uptake of plants or changes in the soil microbial community composition in presence of earthworms. Studies on belowground interactions between earthworms and root herbivores focussed almost exclusively on root-feeding nematodes. These interactions can be either direct (e.g. ingesting of nematodes) or indirect, mediated by changes in host plant performance or biotic and abiotic soil characteristics. Earthworms were documented to counteract the negative effects of root-feeding nematodes on plants. Consistently, earthworm-worked soils (vermicompost) have been reported to reduce numbers of root-feeding nematodes and plant damage by aboveground herbivores. The results suggest context dependent impacts of earthworms on herbivore performance and an alleviation of herbivore damage of plants by earthworms, besides their well-known effects on plant growth. This knowledge is crucial for understanding the impact of earthworms on plants in natural environments, and may be applied as alternative plant protection in sustainable agriculture.