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

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. (C) 1996 Academic Press, Inc.