Original article Interactions between earthworms and plant-parasitic nematodes Johnny Boyer a, * , Georges Reversat b , Patrick Lavelle b , André Chabanne c a CIRAD, UPR Système Ingénierie Agronomique, 10900 Bangkok, Thailand b Institut de Recherche pour le Développement, Centre de Bondy, 32 Av. Henri Varagnat, 93143 Bondy Cedex, France c CIRAD, UPR Système Ingénierie Agronomique, F-34398 Montpellier, France article info Article history: Received 1 May 2013 Received in revised form 17 October 2013 Accepted 18 October 2013 Available online 30 October 2013 Handling editor: Stefan Schrader Keywords: Nematodes Earthworms Pontoscolex corethrurus Pratylenchus zeae Heterodera sacchari Interactions abstract Earthworms can ingest large amounts of soil and litter and thus many nematodes. Several studies have actually shown a decrease in nematode populations in the presence of earthworms. We studied in- teractions between earthworms (the tropical peregrine Pontoscolex corethrurus) and plant-parasitic nematodes (Heterodera sacchari and Pratylenchus zeae) in the laboratory. In the presence of earthworms, we observed a significant decrease in populations of P. zeae in the rhizosphere of Oryza sativa after 6 weeks (1st generation), and 12 weeks (2nd generation), respectively, in comparison to a control with no earthworms. A parallel experiment with H. sacchari and P. corethrurus showed that H. sacchari cysts were ingested by earthworms with the soil, and the interaction between the gut and the gut contents of P. corethrurus and H. sacchari showed that i) populations of cysts had decreased 5 weeks (1st generation) after the start of the experiment, and ii) the total number of eggs and infesting larvae (J2 alive) had decreased. Ó 2013 Published by Elsevier Masson SAS. 1. Introduction Earthworm biomass accounts for a major share of the soil fauna in many tropical humid natural ecosystems [16]. Geophagic worms consume large amounts of soil organic matter and passively digest nematodes at the same time. It is now well known that earthworms can reduce free soilborne nematode populations as well as plant parasitic nematodes [1,3,6,28,31,32]. The impact of earthworms on nematodes can also depend on the situation, sometimes leading to contrary results. In Festuca rubra monocultures, a reduction in nematodes in the presence of Aporrectodea caliginosa has been noted, but with a concomitant increase in the abundance of nem- atodes in a mixture of plants including eight grass species [12]. Other studies have shown better resistance/tolerance of plants against plant parasitic nematodes in the presence of earthworms, without any modification in the nematode abundance [2,13]. The ingestion of soil organic matter by endogeic earthworms has an impact over a broad time scale. Intestinal digestion, which takes 2e4 h, is accompanied by significant mineralization of phosphorus and nitrogen in particular. Inside newly deposited casts, the fresh organic matter is progressively reorganised over the following days or weeks [30]. Over a longer period, the confine- ment of organic matter within the compact structure of the cast blocks the mineralization process for as long as the cast lasts [5,14,15]. Numerous studies have clearly illustrated the positive rela- tionship between the abundance of earthworms and increased productivity of certain cultivated plants [4,13,25]. This favourable effect is generally attributed to chemical (availability of mineral elements) and physical (structure, porosity) earthworm-induced modifications in the soil [15,18,29]. Considering the possible ef- fects of earthworms on nematodes, i.e. by passive ingestion or by physical, chemical or microbiological modification of their envi- ronment, the observed improvement in plant productivity during these experiments could partly be due to the antagonistic effect of earthworms on plant parasitic nematodes. We therefore conducted laboratory experiments to assess the possibility of such an effect by studying interactions between the earthworm Pontoscolex corethrurus and overall populations of two plant parasitic nematodes (Pratylenchus zeae and Heterodera sacchari). 2. Materials and methods The earthworms, P. corethrurus (commonly found in tropical soils) used in this study were from the island of Reunion (France), * Corresponding author. CIRAD Office, 3rd Floor Research-Development Building, Kasetsart University, Bangkok 10900, Thailand. Tel.: þ66 (0) 2942 7627; fax: þ66 (0) 2942 7628. E-mail address: johnny.boyer@cirad.fr (J. Boyer). Contents lists available at ScienceDirect European Journal of Soil Biology journal homepage: http://www.elsevier.com/locate/ejsobi 1164-5563/$ e see front matter Ó 2013 Published by Elsevier Masson SAS. http://dx.doi.org/10.1016/j.ejsobi.2013.10.004 European Journal of Soil Biology 59 (2013) 43e47