Evaluating Metarhizium brunneum F52 microsclerotia in hydromulch formulations using different tackifiers under forest and orchard conditions

Authors: GOBLE, TARRYN - Cornell University; GARDESCU, SANA - Cornell University; Jackson, Mark; HAJEK, ANN - Cornell University

Submitted to: BioControl
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/24/2017
Publication Date: 8/7/2017
Citation: Goble, T.A., Gardescu, S., Jackson, M.A., Hajek, A.E. 2017. Evaluating Metarhizium brunneum F52 microsclerotia in hydromulch formulations using different tackifiers under forest and orchard conditions. BioControl. 62:769-778. https://doi.org/10.1007/s10526-017-9835-7.
DOI: https://doi.org/10.1007/s10526-017-9835-7

Interpretive Summary: Many insect pests including the invasive Asian longhorned beetle (ALB) bore into tree bark laying eggs that grow into foraging larvae that often kill the tree. We are evaluating the use of the biocontrol fungus Metarhizium brunneum (Mb) to control the ALB. One approach is to coat tree bark with a structure of Mb called a microsclerotium. When dried microsclerotia of Mb are rehydrated, they produce spores that infect and kill ALB or other susceptible insect pests. Using a hydromulch spray, such as those used to cover grass seed, microsclerotia of Mb can be attached to the surface of trees. In this study, we evaluated various hydromulch tackifiers such as psyllium and xanthan gum to test their ability to stick hydromulch and microsclerotia to trees. We also evaluated their persistence and biological control efficacy when exposed on trees in a forest and an orchard. Results showed that hydromulch retention was excellent and not affected by the tackifier used. Greater numbers of infective spores were observed on forest samples when compared to orchard samples although the killing of ALBs was unaffected by the hydromulch coated bark being placed in an orchard or forest. These results suggest that lower cost tackifiers can be used to attach hydromulch with Mb microsclerotia to trees and that their use in forests or orchards was equally effective. The application of microsclerotia of Mb using hydromulch shows promise for controlling ALB in forests and possibly other tree-inhabiting insect pests in orchards.

Technical Abstract: Microsclerotia of the entomopathogenic fungus (Metarhizium brunneum Petch strain F52; Hypocreales: Clavicipitaceae) were sprayed in a hydromulch formulation onto wood samples to test persistence and biological control efficacy when exposed on forest and orchard trees. The density of viable conidia and retention of hydromulch were not significantly affected by the tackifier in the formulation (psyllium, xanthan, or a mixture of both). Forest samples had a maximum conidial density and more viable conidia (7.2 × 105 conidia cm-2) than orchard samples (1.4 × 105 conidia cm-2). Increased rainfall, temperature and the time that samples were outdoors were critical factors for conidial density. Asian longhorned beetles [Anoplophora glabripennis (Motschulsky); Coleoptera: Cerambycidae] exposed to orchard samples in laboratory bioassays did not have significantly less mortality compared to forest samples, indicating that hydromulch may be feasible in open sunny conditions, if sufficient moisture is present.