Zhenggao Xiao, Xie Wang, Julia Koricheva, Alan Kergunteuil, Renee-Claire Le Bayon, Manqiang Liu, Feng Hu and Sergio Rasmann
Already Charles Darwin in his book “The formation of vegetable mould, through the action of worms, with observations on their habits” (1881), acknowledged the fundamental role of earthworms as promoters of soil and plant health. Since then, a huge amount of research has indeed shown that earthworms, through their casting and burrowing behaviour, can increase soil nutritional qualities, and in turn favour plant growth and performance. Within this context, researchers have asked more recently if earthworms could also favour increased plant resistance against attack by herbivores. While still relatively young, this literature has already shown several contrasting patterns of earthworms either by increasing, decreasing, or having no effect on herbivores.
With this work, we therefore attempted to summarize all current literature, and by performing a meta-analysis, we specifically asked if earthworms could indirectly increase resistance against herbivores.
We found that earthworm presence in the soil stimulated plant growth (particularly aboveground biomass) and increased plant nitrogen content. We also found that earthworms decreased plant resistance against phloem-feeders (aphids), but didn’t notably affect plant resistance against chewing herbivores and increased plant resistance against cell-feeders (e.g. thrips). However, the final outcome of these complex interactions depended on the biological and functional identity of herbivores and earthworms. We therefore argue that future research on how earthworms change plant physiology is needed to underpin the exact mechanisms mediating the indirect