Alternative Food for Litter-Inhabiting Predators Decreases Thrips Densities and Above-Ground Plant Damage

Abstract

Predatory mites are the most successful group of natural enemies of plant pests, but the potential of soil predatory mites to control pests, especially those that are partially edaphic, has been relatively underexploited. Here, we report on the identification of a predatory soil mite, obtained from a commercial rose greenhouse, capable of controlling the thrips Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae) in the presence or absence of alternative food supplied to the litter. We first sampled litter from the greenhouse and applied it to the base of rose (Rosa sp. L., Rosales: Rosaceae) plants, either with or without Carpoglyphus lactis (L.) (Acari: Carpoglyphidae), a mite commonly found in the litter layer in rose greenhouses, as alternative food. Subsequently, the plants were infested with F. occidentalis and their densities were monitored. Larvae of this thrips species feed on above-ground plant parts, causing significant damage; prepupae and pupae live in the litter layer where they can be attacked by soil-dwelling predators. Densities of thrips and damage on above-ground plant parts were significantly reduced when litter-inhabiting predators, predominantly Cosmolaelaps sabelisi Sierra-Monroy & Rueda-Ramírez (Acari: Laelapidae) and Proctolaelaps pygmaeus (Müller) (Acari: Melicharidae), were supplied with the alternative prey. Subsequent predation tests showed that the latter did not attack thrips pre-pupae, and a final experiment on rose plants showed that C. sabelisi alone significantly reduced thrips densities on the above-ground plant parts, presumably by feeding not only on the prepupae and pupae in the soil, but also on the larvae on the aboveground plant parts. Thus, we identified a new candidate natural enemy for thrips control.