Compatibility of Metarhizium anisopliae with Calpurnia aurea leaf extracts and virulence against Rhipicephalus pulchellus

Abstract

Leaf extracts of Capurnia aurea (Fabaceae) have been reported to attract ticks and can be considered for use in combination with entomopathogenic fungus in an autodissemination approach, whereby ticks that are attracted to baited traps are infected with the inoculum. Bioassays were undertaken to assess the compatibility of aqueous, methanol and acetone extracts of C. aurea with conidia of Metarhizium anisopliae sensu stricto (ss) (Hypocreales: Clavicipitaceae) isolate ICIPE 7 in terms of mycelial growth, conidial production and spore viability. Aqueous extract of C. aurea was compatible with the fungus at all the concentrations tested whereas methanol and acetone extracts inhibited all the fungal growth parameters. The virulence of M. anisopliae formulated in different extracts of C. aurea was also tested against different developmental stages of Rhipicephalus pulchellus in laboratory bioassays. No significant differences in virulence were observed between M. anisopliae applied alone and M. anisopliae formulated in different concentrations of extracts of C. aurea among the larvae, nymphs and adults. However, mortality varied according to the developmental stage, with larval stage being the most susceptible. Aqueous extract was compatible with M. anisopliae and could be therefore mixed together for ‘spot-spray’ treatments as low cost and environmentally friendly technology for tick control in grazing pasture.