Entomopathogenic nematodes for the biocontrol of ticks

Antifungal and antibacterial activities were detected in the hemolymph and gut contents of the cattle tick, Boophilus microplus. A peptide with antibacterial activity from the tick gut contents was purified to homogeneity by reversed-phase chromatography. The molecular mass of the purified peptide was 3,205.7 Da, measured by matrix-assisted laser desorption/ionization mass spectrometry. The amino acid sequence was obtained by Edman degradation and showed that the peptide was identical to a fragment of the bovine alpha-hemoglobin. A synthetic peptide based on the sequence obtained showed characterization data identical to those of the isolated material, confirming its structure. The synthetic peptide was active in micromolar concentrations against Gram-positive bacteria and fungi. These data led us to conclude that the antibacterial activity detected in tick gut contents is the result of enzymatic processing of a host protein, hemoglobin. This activity may be used by ticks as a defense against microorganisms.

This review summarizes the literature about pathogens and predators of ticks and their potential use as biocontrol agents published since the beginning of this century. In nature, many bacteria, fungi, spiders, ants, beetles, rodents, birds, and other living things contribute significantly toward limiting tick populations, as do, for instance, the grooming activities of hosts. Experiments with the most promising potential tick biocontrol agents--especially fungi of the genera Beauveria and Metarhizium and nematodes in the families Steinernematidae and Heterorhabditidae, as well as oxpeckers--are described.