Microsclerotia of Metarhizium brunneum F52 Applied in Hydromulch for Control of Asian Longhorned Beetles (Coleoptera: Cerambycidae)by T. A. Goble, A. E. Hajek, M. A. Jackson, S. Gardescu

Journal of Economic Entomology

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Year
2015
DOI
10.1093/jee/tov013
Subject
Insect Science / Ecology

Text

BIOLOGICAL AND MICROBIAL CONTROL

Microsclerotia of Metarhizium brunneum F52 Applied in

Hydromulch for Control of Asian Longhorned Beetles (Coleoptera: Cerambycidae)

TARRYN A. GOBLE,1,2 ANN E. HAJEK,1 MARK A. JACKSON,3 AND SANA GARDESCU1

J. Econ. Entomol. 1–11 (2015); DOI: 10.1093/jee/tov013

ABSTRACT The entomopathogenic fungus Metarhizium brunneum (Petch) strain F52 (Hypocreales:

Clavicipitaceae) is able to produce environmentally persistent microsclerotia (hyphal aggregates). Microsclerotia of strain F52 produced as granules and incorporated into hydromulch (hydro-seeding straw, water, and a natural glue) provides a novel mycoinsecticide that could be sprayed onto urban, forest, or orchard trees. We tested this formulation against adult Asian longhorned beetles (Anoplophora glabripennis (Motschulsky)) using three substrates (moistened bark, dry bark, absorbent bench liner) sprayed with a low rate (9 microsclerotia granules/cm2) of hydromulch. Median survival times of beetles continuously exposed to sprayed moist bark or absorbent liner were 17.5 and 19.5 d, respectively. Beetles exposed to sprayed dry bark, which had a lower measured water activity, lived significantly longer. When moist bark pieces were sprayed with increased rates of microsclerotia granules in hydromulch, 50% died by 12.5 d at the highest application rate, significantly sooner than beetles exposed to lower application rates (16.5–17.5 d). To measure fecundity effects, hydromulch with or without microsclerotia was sprayed onto small logs and pairs of beetles were exposed for a 2-wk oviposition period in containers with 98 or 66% relative humidity. At 98% humidity, oviposition in the logs was highest for controls (18.36 1.4 viable offspring per female) versus 3.96 0.8 for beetles exposed to microsclerotia. At 66% humidity, fecundities of controls and beetles exposed to microsclerotia were not significantly different. This article presents the first evaluation of M. brunneum microsclerotia in hydromulch applied for control of an arboreal insect pest.

KEY WORDS biological control, Anoplophora glabripennis, entomopathogenic fungus, bioassay, spraying

The entomopathogenic fungus Metarhizium brunneum (Petch) strain F52 (ARSEF 7711) (Hypocreales: Clavicipitaceae) is able to form environmentally persistent microsclerotia (Jaronski and Jackson 2008). These microsclerotia propagules are compact aggregations of hyphae (Jaronski and Jackson 2012), usually 50–600mm in diameter, that are produced under specific submerged liquid culture conditions (Jackson and Jaronski 2009). Sclerotia are well-known in plant pathogenic fungi as desiccation-tolerant persistent structures that reside in soil or plant material (Griffiths 1970, Graham and Griffin 1988, Krikun and Bernier 2009, Jackson et al. 2011). Other entomopathogenic fungi such as

Cordyceps, Hirsutella, Nomuraea rileyi (Farlow) Samson, and Lecanicillium lecanii R. Zare & W. Gams (Ascomycota: Hypocreales) have also been reported to produce microsclerotia (Speare 1920, Sprenkel and

Brooks 1977, Evans and Samson 1982, Wang et al. 2013). To date Metarhizium anisopliae s.l. (Metchnikoff) Sorokin (strains: TM109; MA1200), Metarhizium acridum (Driver and Milner) J.F. Bisch., Rehner and

Humber, and Metarhizium robertsii J.F. Bisch., Rehner and Humber, are species that have also been reported to have successfully produced microsclerotia (Jackson and Jaronski 2009, Mascarin et al. 2014). It has been suggested that the formation of these propagules by entomopathogenic species, particularly those in the genus Metarhizium, is likely an adaptation for living in the soil environment (Jackson et al. 2010), but the extent to which M. anisopliae s.l. microsclerotia might occur naturally in the soil is unknown (Jackson et al. 2010).

Microsclerotia, upon hydration, are capable of producing many infective conidia sporogenically 65 (borne from a conidiophore) (Jackson and Jaronski 2009).

Under ideal laboratory conditions, up to 1.2 1010 conidia can be produced per dry gram of microsclerotia granules made of a 1:1 w/w mixture with clay (Behle et al. 2013). According to Jackson and Jaronski (2009), the formation of microsclerotia and ability to produce these as dry granules represents an innovation for commercial interests using Metarhizium species to control soil-dwelling pests. The main advantage is that other formulations of the fungus (e.g. liquid 1 Department of Entomology, Cornell University, Ithaca, NY 148532601. 2 Corresponding author, e-mail: tazgoble@gmail.com. 3 USDA-ARS-NCAUR, Crop Bioprotection Research Unit, 1815 N

University St., Peoria, IL 61 604.

VC The Authors 2015. Published by Oxford University Press on behalf of Entomological Society of America.

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Journal of Economic Entomology Advance Access published March 2, 2015 culture-produced mycelial pellets, encapsulated fungal biomass, and solid substrate-produced conidia, all either in aqueous suspensions or on nutritive or nonnutritive carriers) make proper placement and homogeneous distribution of the conidia in the soil difficult (Jaronski and Jackson 2008). Microsclerotia granules have been tested for the control of pests such as the sugar beet root maggot, Tetanops myopaeformis (Ro¨der) (Diptera: Ulidiidae), and black-legged ticks,

Ixodes scapularis Say (Acari: Ixodidae) (Jaronski and

Jackson 2008, Jackson and Jaronski 2009, Behle et al. 2013). However, nothing is known of the use of microsclerotia granules to control insect pests in an arboreal environment, which is the subject of this study.

In the biological control of Asian longhorned beetle,

Anoplophora glabripennis (Motschulsky) (Coleoptera:

Cerambycidae), the use and application of M. brunneum strain F52 formulated as fungal bands has previously been tested successfully in the laboratory in the

United States (Shanley et al. 2009, Ugine et al. 2013) and in the field in China (Hajek et al. 2006). However, due to the difficulty of applying these fungal bands high in trees, wrapped around branches or trunks, development of a sprayable formulation of the fungus is being investigated. Therefore, research has now been shifted toward the inclusion of M. brunneum F52 microsclerotia granules (hereafter referred to as Mb