Combined releases of soil predatory mites and provisioning of free-living nematodes for the biological control of root-knot nematodes on ‘Micro Tom tomato’

Soil predatory mites feed on a diverse diet making them excellent candidates for conservation biocontrol. Free-living nematodes (FLN) are commonly found in soils and serve as prey for many acarine predators. Our goal was to determine whether conservation biological control of plant-parasitic nematodes by predators could be enhanced by provisioning FLN with their culture medium (FLNCM) under semi-field conditions. We conducted two experiments on dwarf tomato plants, the first until the beginning of flowering and the second until harvest. The treatments evaluated were with and without: 1) the root-knot nematode Meloidogyne incognita, 2) the predator Stratiolaelaps scimitus, and 3) the FLN Rhabditella axei in its culture medium. In both experiments, gall abundance was lowest in the combined treatment of FLN and predators. Similar reduction in gall abundance occurred when only predators or only FLNCM was added to the soil mix. Additionally, in the FLNCM treatment, foliar macronutrients N and K were significantly higher than the negative control. Our original aim was to use FLN as a supplementary food source for predators in conservation IPM. Based on the significant reduction in gall numbers, and the increase in foliar macronutrients, it is clear that the FLNCM treatment played additional roles. Finally, for demonstration, the predation of M. incognita was visualized in high resolution imaging using a low-temperature-scanning electron microscope. Accordingly, we recommend that future research focus on identifying soil amendments that will foster the establishment of beneficial microbiota, FLN and soil predators for the conservation biological control of soil pests.