Prospects for biological control of livestock ticks, Rhipicephalus appendiculatus and Amblyomma variegatum, using the entomogenous fungi Beauveria bassiana and Metarhizium anisopliae

Abstract

Both Beauveria bassiana and Metarhizium anisopliae induced approximately 30% mortalities in adult Rhipicephalus appendiculatus feeding on rabbits while M. anisopliae induced a mortality of 37% in adult Amblyomma variegatum. Both fungal species induced reductions in engorgement weights, fecundity, and egg hatchability in adult A. variegatum. M. anisopliae reduced fecundity by 94% in A. variegatum. Furthermore, B. bassiana reduced egg hatchability to 0%, while 11% of the infected females failed to lay eggs. In Zebu cattle naturally infested, with R. appendiculatus in the field, both B. bassiana and M. anisopliae induced 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. bassiana and M. anisopliae persisted on cattle ears for 1 and 3 weeks, respectively, after application. Both B. bassiana and M. anisopliae induced a mortality of approximately 100%, 76-95% and 36-64% in larvae, nymphs, and adults, respectively, of R. appendiculatus seeded in grass in the field. Spores of B. bassiana and M. anisopliae mixed with sterilized sand and maintained at 0 and 25 degrees 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