Metarhizium microsclerotia and hydrogel versus hydromulch: testing fungal formulations against Asian longhorned beetles

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

Submitted to: Biocontrol Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/28/2017
Publication Date: 8/4/2017
Citation: Gardescu, S., Hajek, A.E., Goble, T.A., Jackson, M.A. 2017. Metarhizium microsclerotia and hydrogel versus hydromulch: testing fungal formulations against Asian longhorned beetles. Biocontrol Science and Technology. doi: 10.1080/09583157.2017.1362546.

Interpretive Summary: In North America, the Asian longhorned beetle is an invasive insect pest primarily of urban and suburban trees but recently found in forests in Massachusetts. Spores of the insect-killing fungus Metarhizium brunneum (Met) have been shown to infect and kill the Asian longhorned beetle. Because the female beetles lay their eggs on the limbs and trunks of host trees, applying a spore-forming form (microsclerotium) of Met to tree bark by spraying has potential for use as a biological control for the Asian longhorned beetle. Met microsclerotia spray formulations were developed using hydromulch and stickers and incorporate dried microsclerotia that when hydrated for infective spores. In this experiment, Met microsclerotia formulations were exposed on forest trees and the conidia produced by these formulations were tested against Asian longhorned beetle adults. During drought conditions in Ohio, insufficient numbers of infective Met spores were produced by the microsclerotia formulations. With normal seasonal levels of rain in Ohio and New York, the spore yields by Met microsclerotia formulations were sufficient to produce insecticidal concentrations of conidia which persisted on trees for 4-6 weeks. These results suggest that sprayable formulations of Met microsclerotia may be a viable approach for delivering infective quantities of spores of the insect-killing fungus M. brunneum.

Technical Abstract: The efficacy of microsclerotia of Metarhizium brunneum (Petch) (Hypocreales: Clavicipitaceae) strain F52 (ARSEF 7711) was tested using samples that had been exposed on forest trees, allowing time for conidia to be produced. An aqueous mixture of microsclerotial granules (61.3% of dry mass), a straw mulch hydroseeding product (29.4%), xanthan gum as a tackifier (5.4%), and water-absorbing hydrogel (3.9%), was sprayed on small wood-veneer samples attached to tree trunks in Clermont County, Ohio, within the USDA quarantine zone for Asian longhorned beetles (Anoplophora glabripennis (Motschulsky); Coleoptera: Cerambycidae). Samples were collected biweekly from June to August. At each collection date, female beetles in a quarantine laboratory were exposed for 2 d to individual samples. Mortality with the 4-wk samples was faster (ST50 9.5 d) than with samples from 2 or 6–10 weeks, but not as rapid as possible (ST50 6.5 d, using samples incubated at 100% humidity in the laboratory). Conidial density also peaked at 4 weeks, while the sprayed material gradually weathered to 33% of initial dry mass by 10 weeks. A separate field experiment with microsclerotia compared three formulations: the hydrogel-hydromulch mixture, straw hydromulch without gel, or hydrogel alone. Results were highly weather-dependent, but bioassays in August with samples collected after 2 or 4 weeks had ST50s between 8.5–9.5 days, with any of the three formulations. Overall the hydrogel addition did not produce a significant improvement in efficacy, either during dry or rainy periods, and hydrogel alone (without straw mulch) appeared to be an additional viable option.