Effectiveness of above- and below-ground predators in controlling the invasive Thrips parvispinus

Abstract: The invasive Thrips parvispinus spends its prepupal and pupal stages in the soil and the other stages on plant leaves. Its biological control can thus be achieved by releasing a
combination of above- and below-ground predators. Some soil mites have been observed
climbing plants, creating the possibility of their use both above and below-ground. However,
their application in biocontrol remains poorly explored. We tested the effectiveness of the
belowground predatory mite Rhabdocarpais consanguineus, alone and in combination with the above-ground predatory mite Amblyseius swirskii, in controlling T. parvispinus on sweet pepper plants in cages in a greenhouse. We found that R. consanguineus significantly reduced the density of T. parvispinus; however, the level of control was not sufficient to prevent damage of some plants. Amblyseius swirskii, both alone and in combination with R. consanguineus, effectively controlled T. parvispinus. The densities of A. swirskii were lower when R. consanguineus were present than in their absence, either due to competition for the thrips prey or to intraguild predation. In a second experiment, we further investigated this interaction between the two predators. We found that the deutonymphs of R. consanguineus climbed from the soil onto the plants, where they reduced the densities of the larvae of A. swirskii. Despite the occurrence of this negative interaction, the results of the first experiment show that A. swirskii can effectively control T. parvispinus, both alone and in combination with R. consanguineus. The added release of R. consanguineus to plants with A. swirskii did not improve control.