Predatory soil mites: beyond pest control?

Abstract: Cosmolaelaps Berlese n. sp. (Acari: Laeapidae) is a promising soil predator tocontrol a variety of thrips pests. Previously we showed that Cosmolaelaps n. sp., together withCarpoglyphus lactis L. (Acari: Carpoglyphidae) as alternative food in the litter decreasespopulations of Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae) on rose plants.The reduction of pest densities may be directly caused by predation or indirectly through plantmediatedeffects. Here, we evaluated the potential control of three herbivores on vegetables byCosmolaelaps n. sp. First, we tested the effect of Cosmolaelaps n. sp. on the performance ofleaf-dwelling spider mites (Tetranychus urticae Koch (Acari: Tetranychidae) and on two thripsspecies: a species that is known to spend part of its life cycle in the soil (F. occidentalis) and aspecies which life cycle is supposed to be entirely on the plant foliage [Echinothrips americanusMorgan (Thysanoptera: Thripidae)]. The effects on the different pest species densities werevariable. Spider mite densities were not affected by the presence of Cosmolaelaps n. sp., butthrips densities were reduced independently of whether the pest spends parts of its life cycle inthe soil or not. Second, we performed experiments with only clean plants (without herbivoreinfestations) to test whether the presence of Cosmolaelaps n. sp. had an effect on the plantperformance (growth and reproduction). We found that plants with Cosmolaelaps n. sp. in thesoil had a better performance than plants without Cosmolaelaps n. sp. Our results suggest thatthe role of soil predators such as Cosmolaelaps n. sp. in the system is not limited to predationbut may contribute to pest control through plant-mediated indirect effects. The mechanismsunderlying these effects deserve further investigation.