Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/13/2014
Publication Date: 2/20/2014
Publication URL: http://handle.nal.usda.gov/10113/60597
Citation: Behle, R.W., Jackson, M.A. 2014. Effect of fermentation media on the production, efficacy and storage stability of Metarhizium brunneum microsclerotia formulated as a prototype granule. Journal of Economic Entomology. 107(2):582-590.
Interpretive Summary: Economical production of microbes for use as biopesticides for the non-chemical control of insect pests is a limiting factor for their commercialization. This research demonstrates the relationship between production conditions of the insect-killing fungus Metarhizium brunneum Strain F52 and its effectiveness as a biopesticide. Using higher concentrations of protein in the growth media improved production of the fungus and resulted in higher insecticidal effectiveness against larvae of the lesser mealworm (Alphitobius diaperinus Panzer), an important pest of commercial poultry houses that causes millions of dollars of economic losses annually in the United States. The results of this research has improved the ability to produce Metarhizium brunneum Strain F52 with commercial viability and, in general, support efforts to develop biological control agents with the potential to replace chemical insecticides, ultimately providing direct benefits for the biopesticide industry and agriculture with additional benefits to the public and environment.
Technical Abstract: New liquid fermentation techniques for the production of the bioinsecticidal fungus Metarhizium brunneum strain F-52 have resulted in the formation of microsclerotia (MS), a compact, melonized-hyphal structure capable of surviving desiccation and formulation as dry granules. When rehydrated, these MS granules germinate to produce conidia that can infect susceptible insects. Fermentation media containing cottonseed or soy flours as nitrogen sources and formulated at two carbon to nitrogen ratios (C:N), 30:1 or 50:1, were evaluated for production of microsclerotia. Dry MS granule samples were compared for storage stability based on conidia production, and insecticidal activity against larvae of the lesser mealworm, Alphitobius diaperinus Panzer, using a potting soil bioassay. Cottonseed and soy flours were equivalent for production, MS granule viability, and insecticidal activity. Fermentation media containing higher nitrogen concentrations (30:1 C:N) resulted in greater biomass accumulation and greater production of conidia from granules regardless of the nitrogen source. MS granules made with M. brunneum cultures grown in media with 30:1 C:N produced 8.5 ×109 conidia g-1 of granules, significantly higher than MS granules made using fungus produced using 50:1 C:N media (5.5 ×109 conidia g-1 dry MS granules). The LC50 for larval mortality was 1.99 x 106 conidia per cup, equivalent to application rates of 233 and 362 µg granules per cup for granules made from high and low nitrogen concentrations, respectively. Higher initial conidial production was reflected in longer storage stability at 25o C with half-lives estimated at 3.7 and 1.7 weeks for 30:1 and 50:1 C:N ratios, respectively. These results support further evaluation of MS granule formulations for the control of soil inhabiting insect pests.