Biocontrol of Ticks (Acari Ixodidae) by Scopulariopsis brevicaulis and Metarhizium anisopliae

Abstract

A study was conducted to evaluate the use of fungi as an alternative method for tick control instead of the currently used chemical acaricides to overcome their known drawbacks. Scopulariopsis brevicaulis was isolated from Amblyomma lepidum for the first time. Pathogenicity of the fungus was tested on different developmental stages of Hyalomma anatolicum anatolicum and A. lepidum in comparison with Metarhizium anisopliae which was obtained from the International Centre of Insect Physiology and Ecology, Kenya. Different concentrations of spore suspensions (curative dose 2.4x107 spores/ml) of the two fungi were used. High mortality of immature stages was observed. Mortality of flat adult ticks was also reported. There was a strong positive correlation (r= 0.99) between the concentration of the spores and mortality of flat adult ticks. Culture filtrate of S. brevicaulis was also tested. It revealed the same effect as the sporesuspension. Both fungi affected the reproductive potential of females A. lepidum and H .a. anatolicum. Moulting percent age of engorged larvae and hatching of eggs were significantly reduced (P<0.05). Infection of eggs was also demonstrated which suggests transovarian transmission of the fungus. The study also showed persistence of S. brevicaulis for 60 days on rabbit's ears. This finding suggests the ability of transmission of infection to healthy ticks through direct contact. Both fungi showed ability to adhere to the cuticles and penetrate tick integuments. Conidia of both fungi XIII were isolated from their internal tissues. This finding is important in considering fungi as bioinsecticides. Gas chromatography mass spectrometry of S. brevicaulis culture filtrate recovered ketonic compounds and fatty acids which might be toxic to ticks. Reduction in tick haemocyctes was shown which reflects the effect of these metabolites on the defense response of ticks.