Manipulating plant-arthropod conversations to improve conservation biological control of mites

Abstract

The potential of using synthetic herbivore-induced plant volatiles (HIPV) (e.g., methyl salicylate, MeSA) as a cultural tool to enhance conservation biological control of mites is being researched in commercially grown hops in Washington State, USA. Compared to unbaited blocks, hop yards baited with controlled release sachet (CRS) dispensers of synthetic MeSA recruited larger (3-5x) populations of spider mite predators: Stethorus spp. (Coleoptera: Coccinellidae), Orius tristicolor (Hemiptera: Anthocoridae), Geocoris pollens (Hemiptera: Geocoridae), Deraeocoris brevis (Hemiptera: Miridae), Chrysopidae, Hemerobiidae, Nabidae, Thripidae. The enhanced community of mite predators controlled spider mite populations in MeSA-baited hops without miticide intervention. All unbaited blocks required at least one miticide for spider mite control. Direct application of natural MeSA (oil of wintergreen) to hop plants contained in canola oil or rosemary/peppermint oil pesticide formulations, resulted in greater attraction of two mite predators (O. tristicolor and Stethorus spp.) to treated than to untreated plants. MeSA-mediated stimulation of the plants to produce predator-attracting volatiles is suggested as the likely mechanism. The use of synthetic or natural versions of HIPV/plant-signaling compounds like MeSA as `Herbivore-Induced Plant Protection Odors' (HIPPOs), has the potential to provide a novel yet practical strategy for improving the efficacy and reliability of conservation biological control of mites in a variety of agricultural ecosystems.