Efficacy of two entomopathogenic fungi, Metarhizium brunneum, strain F52 alone and combined with paranosema locustae against the migratory grasshopper, Melanoplus sanguinipes, under laboratory and greenhouse conditions

Authors: DAKHEL, WAHID - University Of Wyoming; LATCHININSKY, ALEXANDRE - University Of Wyoming; Jaronski, Stefan

Submitted to: Insects
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/29/2019
Publication Date: 3/30/2019
Citation: Dakhel, W., Latchininsky, A., Jaronski, S. 2019. Efficacy of two entomopathogenic fungi, Metarhizium brunneum, strain F52 alone and combined with paranosema locustae against the migratory grasshopper, Melanoplus sanguinipes, under laboratory and greenhouse conditions. Insects. https://doi.org/10.3390/insects10040094.
DOI: https://doi.org/10.3390/insects10040094

Interpretive Summary: Microbial control of grasshopper outbreaks is strongly desired not only in countries with locust outbreaks, but also in the United States where most of the western states suffer periodic outbreaks of a number of grasshopper species. While several insect pathogenic fungi have shown promise delivery of the infectious spores by spray application has severe limitations. A bait formulation could increase efficacy by concentrating spores on a few pieces of bait Paranosema locustae has been commercial for at least three decades for use against grasshoppers, but it is effective only against the youngest nymphal instars. Combining the two agents on a bait increased efficacy in a synergistic manner. These findings open the way for a more efficient, and cost effective use of these microorganisms to manage grasshopper populations.

Technical Abstract: Grasshopper outbreaks cause significant damage to crops and grasslands in US. Chemical control is widely used to suppress these pests but it reduces environmental quality. Biological control of insect pests is an alternative way to reduce the use of chemical insecticides. In this context, two entomopathogenic fungi, Metarhizium brunneum strain F52 and Paranosema locustae were evaluated as control agents for the pest migratory grasshopper Melanoplus sanguinipes under laboratory and greenhouse conditions. Third-instar grasshopper nymphs, reared in the laboratory, were exposed up to fourteen days to wheat bran treated with different concentrations of each of the fungi alone or the two pathogens combined. In the greenhouse, nymphs were placed individually in cages where they were able to generate fevers by basking, and treated with each pathogen alone or in combination. Mortality was recorded daily and presence of fungal outgrowth in cadavers was confirmed by recording fungal mycosis for two weeks’ post-treatment (PT). For combination treatment, the nature of the pathogen interaction (synergistic, additive, or antagonistic effects) was also determined. In laboratory conditions, all treatments except P. locustae alone resulted in grasshopper mortality. The application of the pathogen combinations caused 75% and 77%, mortality for lower and higher concentrations, respectively than each of the pathogens alone. We infer a synergistic effect occurred between the two agents. In greenhouse conditions, the highest mortalities were recorded in combination fungal treatments with a M. brunneum dose (60% mortality) and with a combination of the two pathogens in which M. brunneum was applied at high rate (50%) two weeks after application. This latter combination also exhibited a synergistic effect. Exposure to the P. locustae treatment did not lead to mortality until day 14 PT. We infer that these pathogens are promising for developing a biopesticide formulation for rangeland pest grasshopper control.