Evaluating different carriers of Metarhizium brunneum F52 microsclerotia for control of adult Asian longhorned beetles (Coleoptera: Cerambycidae)

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

Submitted to: Biocontrol Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/24/2016
Publication Date: 5/24/2016
Citation: Goble, T.A., Gardescu, S., Jackson, M.A., Hajek, A.E. 2016. Evaluating different carriers of Metarhizium brunneum F52 microsclerotia for control of adult Asian longhorned beetles (Coleoptera: Cerambycidae). Biocontrol Science and Technology. 26(9):1212-1229. doi: 10.1080/09583157.2016.1192103.

Interpretive Summary: The Asian longhorned beetle (ALB) is an invasive insect pest that poses a serious threat to the sugar maple forests of the Northeastern United States. The ALB bores into tree bark laying eggs that grow into foraging larvae that often kill the tree. Various control measures are being developed for the ALB including the use of the non-chemical, biocontrol fungus Metarhizium brunneum (Mb). The fungus Mb produces spores that are capable of infecting and killing the ALB. We have developed commercially-viable, liquid fermentation method for producing a resistant structure of MB called a microsclerotium. Microsclerotia of Mb remain viable after drying and when rehydrated produce infective spores. Using a hydromulch spray, microsclerotia of Mb can be attached to the surface of trees. When rewetted, the microsclerotia attached to the trees produce infective spores that infect and kill foraging ALB. In these experiments, various microsclerotial granule formulations composed of Mb microsclerotia + clay, microcrystalline cellulose, or diatomaceous earth were tested for their ability to produce infective spores. Results from these studies showed that all 3 carriers performed equally well in terms of viable spore production and that all could be used in commercial formulation for microsclerotial granules of the bioinsecticide Mb.

Technical Abstract: Microsclerotia (MS) of Metarhizium brunneum strain F52 (Hypocreales: Clavicipitaceae), were processed as granules using three carriers: kaolin clay, microcrystalline cellulose (MCC) or diatomaceous earth (DE). In a series of experiments aimed at comparing viable conidial production and subsequent percent conidial germination, each MS carrier type was hydrated using a decreasing range of water activities on glycerol-amended or polyethylene glycol (PEG200)-amended media. Conidial production and percent germination of conidia declined significantly as water activity was lowered. All three carrier types produced > 2-6 ×10**9 viable conidia/gram at higher water activities (aw >0.987) but were still capable of producing 2.9 ×10**7 ± 1.6 ×10**6 conidia/g (30% glycerol aw=0.883) and 1.9 ×10**7 ± 6.5 ×10**6 conidia/g (30% PEG200 aw=0.924) at the lowest tested water activities. Average viable conidial production by MCC granules in a hydromulch formulation incubated in a high relative humidity treatment (>91%) was 6.08 ×10**8 ± 1.1 ×10**8 conidia/g but dropped to 3.30 ×10**7 ± 7.4 ×10**6 conidia/g in a hydromulch treatment incubated at lower relative humidity (<79%). The three MS carrier types were sprayed onto 0.4 m length logs with or without hydromulch formulation. The median survival times of Asian longhorned beetles, Anoplophora glabripennis (Coleoptera: Cerambycidae), exposed by climbing double the length of the logs (i.e. 0.8 m) of hydromulch-treated bark were 16.5-20.5 d while beetles exposed to logs without hydromulch formulation had median survival times of 22-25.5 d. Overall, experiments showed that there were few biologically-significant differences between the MS carrier types.