Fungal Biopesticide for cattle tick and buffalo fly control

Summary

Cattle ticks (Rhipicephalus (Boophilus) microplus) and buffalo flies (Haemotobia exigua irritans) are serious pests of cattle in northern Australia. Important control options include chemical treatments (acaricides and insecticides) applied in strategic control programs along with breeding tick resistant cattle genotypes and pasture management. However there is scope for more control options to effectively manage these serious pests including a fungal biopesticide based on Metarhizium anisopliae.
DEEDI investigations found that some Australian isolates of M. anisopliae are extremely effective at killing ticks in the laboratory, with death occurring in 100% of ticks within two days (Leemon & Jonsson, 2008). However a series of field and pen trials have provided inconclusive evidence as to the commercial potential of a fungal biopesticide for tick control (Leemon et al, 2008, Leemon, 2010). Previous DEEDI investigations have also noted that buffalo flies are extremely susceptible to Metarhizium infection under laboratory conditions. During one of cattle tick trial it was found that buffalo flies netted from biopesticide treated cattle had high levels of Metarhizium infection and died faster after laboratory incubation than flies netted from untreated cattle. The current study was therefore undertaken to repeat investigations into the efficacy and commercial potential of a fungal biopesticide in controlling cattle ticks under field conditions and include an appraisal of the fungal biopesticide for buffalo fly control.
Two field trials were conducted in this study. The first trial aimed to investigate the therapeutic and short-term persistent (prophylactic) efficacy of a fungal biopesticide against artificial burdens of cattle tick on cattle under field conditions. Two dose rates of a Metarhizium formulation were compared to a negative „untreated‟ control group and a positive control group treated with a common commercial acaricide. Cattle from the first trial were retained for the second trial in which the effect of the fungal biopesticide on buffalo fly populations and natural infestations of ticks on cattle were appraised. Two different Metarhizium formulations were applied to cattle, one a spray formulation applied once and the other a “pour-on” formulation applied three times a week for two weeks.
The results of the two trials showed that a Metarhizium based fungal biopesticide has potential for the control of buffalo flies but has limited efficacy against cattle ticks.
The results of the study suggest that the conditions required to achieve a tick control efficacy greater than 40% with a fungal biopesticide are too narrow to be practical for commercial development with the performance affected by too many variables. While some efficacy was apparent in both trials in this study, and in previous tick studies on animals (Leemon et al, 2008, Leemon, 2010), there was no evidence of the outstanding and consistent results required to justify further research into the commercial development of a fungal biopesticide for tick control on cattle.
Both the biopesticide spray and “pour-on” formulations resulted in huge decreases in buffalo fly populations on treated cattle and the fungal spores appeared to remain viable in the animal coat for up to two weeks after application. The spray formulation caused a rapid decrease in buffalo fly numbers with scarcely five flies per side seen on the sprayed animals after two days. This effect gradually decreased with time and fly numbers subsequently increased. However buffalo fly numbers on these animals did not reach an economic threshold (300+) until nearly three weeks after treatment. The “pour on” strategy was even more effective than the spray strategy giving greater control with less formulation. The number of buffalo flies on “pour on” treated cattle decreased to 1-50 flies /side /animal and stayed down for until at least a week after the last application. Throughout the trial the untreated cattle carried buffalo fly infestations of 500+ flies /side / animal.
The results of this project suggest that a fungal biopesticide for buffalo fly control has potential. A biopesticide would be an important addition to current control strategies, particularly those that utilise walk through buffalo fly traps, back rubbers and dust bags. However further research is required to optimise both the formulation and application strategies. It is recommended that further research into the development of a fungal biopesticide for buffalo fly control is supported through laboratory and field studies. The results of this study also indicate that a fungal biopesticide for tick control is subject to too many variables to deliver a consistent and high level of tick control on animals across a range of climatic regions and seasons. Therefore further development of a fungal biopesticide for cattle tick control, is not recommended.