SUSCEPTIBILITY OF THE AUSTRALIAN PLAGUE LOCUST, CHORTOICETES-TERMINIFERA, AND THE WINGLESS GRASSHOPPER, PHAULACRIDIUM-VITTATUM, TO THE FUNGI METARHIZIUM SPP

Chortoicetes terminifera (fourth instar) and Phaulacridium vittatum (f ourth and fifth instar) nymphs were inoculated topically with 7500 con idia/insect in 0.2 mul of raw peanut oil with each of five isolates of Metarhizium spp. Three isolates of M. flavoviride from acridids were more virulent than two isolates of M. anisopliae isolated from either termite nest material in Australia or from soil in Burma. Similar diff erences between isolates were obtained when the screening was repeated against fifth-instar C. terminifera nymphs at a lower dose of 750 con idia/insect. At the higher dose, FI985 (ARSEF 324) from an Australian acridid gave a MLT (median lethal time) of 4.3 days for C. terminifera at 29-degrees-C and 5.4 days for P. vittatum at 26-degrees-C. The oth er two isolates of M. flavoviride tested were similar in their pathoge nicity. The susceptibility of the two acridids for FI985 was further t ested in a bioassay using five doses. Based on the resultant LD50 valu es, C. terminifera [LD50 - 417 (220-721) conidia/insect] was three tim es more susceptible than P. vittatum [LD50 = 1,212 (689-1900) conidia/ insect], though this difference was not significant (P > 0.05). Moltin g within 24 h of inoculation had no effect on subsequent mortality. Th e high susceptibility of the two most important acridid pests in Austr alia to a locally derived isolate encourages the development of M. fla voviride as a more environmentally benign alternative to fenitrothion spraying. (C) 1994 Academic Press, Inc.