Prospects for Biological Control of Livestock Ticks,Rhipicephalus appendiculatusandAmblyomma variegatum,Using the Entomogenous FungiBeauveria bassianaandMetarhizium Anisopliae

Abstract

BothBeauveria bassianaandMetarhizium anisopliaeinduced approximately 30% mortalities in adultRhipicephalus appendiculatusfeeding on rabbits whileM. anisopliaeinduced a mortality of 37% in adultAmblyomma variegatum.Both fungal species induced reductions in engorgement weights, fecundity, and egg hatchability in adultA. variegatum. M. anisopliaereduced fecundity by 94% inA. variegatum.Furthermore,B. bassianareduced egg hatchability to 0%, while 11% of the infected females failed to lay eggs. In Zebu cattle naturally infested, withR. appendiculatusin the field, bothB. bassianaandM. anisopliaeinduced high mortalities ranging from 76–85%, a remarkable reduction in fecundity (85–99%), and a significant reduction in egg hatchability (94–100%). When incubated in organophosphate acaricides for up to 120 hr, both fungi retained their normal growth and morphological characteristics.B. bassianaandM. anisopliaepersisted on cattle ears for 1 and 3 weeks, respectively, after application. BothB. bassianaandM. anisopliaeinduced a mortality of approximately 100%, 76–95% and 36–64% in larvae, nymphs, and adults, respectively, ofR. appendiculatusseeded in grass in the field. Spores ofB. bassianaandM. anisopliaemixed with sterilized sand and maintained at 0 and 25°C maintained good viability for over 12 months (B. bassiana) and for 8 months (M. anisopliae) and no significant difference was observed in spores stored in the two different temperatures.