Research and development of a newly discovered, effective grasshopper biocontrol agent found in Canadian prairie soil

Project Code BPI06-070

Project Lead

Dan Johnson  University of Lethbridge

Objective

To determine the effectiveness of a newly identified Canadian fungus, Metarhizium anisopliae, as a potential biopesticide for grasshoppers

Summary of Results

Background

Management of pest grasshoppers in Canada continues to rely on chemical insecticides, primarily organophosphates, carbamates, and pyrethroids. Some of the older insecticide uses are being lost to regulatory re-evaluation by the Pest Management Regulatory Agency (PMRA). Given that grasshopper outbreaks are sporadic and tend to be exacerbated by warm and dry weather, future outbreaks are likely to be longer or more frequent if the recent warming trend continues. Therefore, safer alternative control options are needed for a sustainable grasshopper management system away from full reliance on chemical tools.

Currently, there are no biological agents registered in Canada for grasshopper control. However, an indigenous fungus discovered in Canadian Prairie (Alberta) soil, Metarhizium anisopliae var. anisopliae, shows good biocidal activity against grasshoppers. The 2-year project aimed to determine the effectiveness of this potential biocontrol agent for grasshopper control and its impact on non-target species. The goal was to generate necessary efficacy data to meet registration and commercialization requirements for the potential biopesticide.

Approach

The project was conducted at the University of Lethbridge, Alberta from 2006 to 2008. It involved a number of laboratory and field experiments, including grasshopper control efficacy and environmental testing of spray treatments with native Metarhizium isolate (strain S54) in comparison to commercially available Metarhizium strains (e.g. Met52 or Green Muscle) originating from other regions of the world. Additional tests included determination of the lethal dose (LD) and lethal time (LT) of the biocontrol agent on early instars (1st to 4th) of native grasshoppers, testing impact on non-target organisms as well as the relationship between weather, grasshoppers and biocontrol efficacy.

Five major grasshopper species, common for the Prairie region, and a range of S54 spore concentrations (0, 103, 104, or 105) were included in the laboratory tests, under a variety of pest (e.g. age, species, diet) and environmental conditions. A previously developed Deoxyribonucleic acid (DNA)-based monitoring method was used to detect and differentiate the native Metarhizium fungus isolate from other fungal species and strains. One field test consisted of a large-cage experiment using three spore concentration rates applied as a spray with vegetable oil carrier. Abundance and age classes of naturally occurring grasshopper species was monitored prior to and after treatment.

Pathogenicity and biocidal effect of the native strain was evaluated as percent mortality and percent sporulation in the population of grasshopper cadavers over 1-15 days following spray treatment with the spore dilutions.

Results

Overall, the pathogenicity of native fungal biocontrol agent M. anisopliae var. anisopliae isolate S54 to major pest grasshopper species was confirmed. It provided effective grasshopper mortality, ranging from 78 -100% within 9 days post-treatment. Most importantly, 100% mortality was achieved 7 days post-treatment for the two-striped grasshopper, the main pest species in the region. These levels of efficacy are comparable to other, closely related and highly virulent registered strains of M. anisopliae var. acridum.

Also, sporulation of the fungus on grasshopper cadavers ranged from 70-100% of treated insects. About 10,000 spores per grasshopper appear to be highly effective in causing death. The sprayed Metarhizium spores attach to the surface of the insect, germinate and begin to grow, penetrating the insect’s exoskeleton. The fungus grows very rapidly inside the insect body leading to death. Under ideal conditions, it usually takes 3 to 5 days, once the insect is exposed to the biocontrol for death to occur.

Infection of adult grasshoppers with isolate S54 resulted in time to 50% dead (LT50) of 8 to 12.5 days and 90% dead (LT90) of 14.5 to 21 days for doses of 100,000 (105) and 10,000 (104) spores per insect, respectively.

This entomopathogenic (insect disease causing agent) fungus represents the first highly virulent indigenous control agent of grasshoppers in North America. Unlike most insect-killing fungi, S54 showed good efficacy under relatively warmer conditions. No harmful effects were observed on vertebrate (livestock, wildlife) species exposed to the fungus.

Consultations with the PMRA and information generated through this project contributed to fulfilling part of the PMRA’s registration requirements for the new S54 microbial agent. This marked a step forward to the development and registration of a new biopesticide from this native Canadian fungus.

The S54 strain was subjected to more scale up studies and trials following the completion of this project. It shows promise as a safe and effective option to manage grasshopper outbreaks in both conventional and organic production systems. Protected areas (e.g. pasture and grassland) will also benefit from this biological option of grasshopper control. The strain is currently under development as a microbial biopesticide for grasshopper control.

For more information please contact Dr. Dan Johnson.

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