Myco-insecticide for nuisance fly control in cattle feedlots

Summary

​Previous studies demonstrated that Queensland-isolated strains of the entomopathogenic fungus Metarhizium anisopliae infected and killed flies and that the efficacy of some strains was high (typically 80-100% mortality). This project built on the results of this work and developed ULV spray and bait formulations of Metarhizium suitable for use in the control of nuisance flies on cattle feedlots. The best strains from the previous feedlot project B.FLT.0326 were selected from the DAF fungal collection, passaged through flies and retested for efficacy. This confirmed M16 as the most effective strain, with attributes making it suitable for mass production. A number of modifications were made to optimise the spore production system and achieved yields in line with expectations for economic commercial production. The strain has also been shown to be effective against other veterinary pests including sheep lice, sheep blowflies, buffalo flies and cattle ticks, suggesting other markets and potentially increasing its attractiveness for commercialisation.

As a result of laboratory testing, two ULV and two VLV formulations were selected for testing in field cage studies. The ULV formulations consisted of M. anisopliae spores suspended in canola oil or peanut oil mixed with Shellsol T (30:70) whereas the VLV formulations consisted of M. anisopliae spores suspended in 2% EAOs Horti Oil or Codacide, with 1% molasses. The ULV oil/Shellsol T formulations gave consistently better effect than the VLV emulsions and the Canola oil/Shellsol T ULV form marginally better effect than the Peanut oil/Shellsol formulation. As a result the 30:70 Canola/Shellsol formulation (30:70) (46g spores/L) was chosen for testing in feedlots.

Spraying led to a large increase in viable spore numbers on vegetation in the spray areas for at least 2 weeks post spraying and was shown to produce a measurable infection rate (42%) and mortality of flies (44%) collected immediately after spraying. Although significant mortality could not be demonstrated from the effects of spraying after this time, previous tests with flies exposed to treated vegetation one week and two weeks after spraying indicated mortality of 48% -75% and 15% respectively. The full analysis showed statistically significant reductions in fly numbers estimated as 20%, 23%, 31% and 9% by the fly index, visual scores, sticky cards and spot cards respectively. There was also a significant accumulative effect on fly mortality over the spraying period.