Susceptibility of the Australian Plague Locust, Chortoicetes terminifera, and the Wingless Grasshopper, Phaulacridium vittatum, to the Fungi Metarhizium spp.

Abstract Chortoicetes terminifera (fourth instar) and Phaulacridium vittatum (fourth and fifth instar) nymphs were inoculated topically with 7500 conidia/insect in 0.2 μl 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 differences between isolates were obtained when the screening was repeated against fifth-instar C. terminifera nymphs at a lower dose of 750 conidia/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°C and 5.4 days for P. vittatum at 26°C. The other two isolates of M. flavoviride tested were similar in their pathogenicity. The susceptibility of the two acridids for FI985 was further tested in a bioassay using five doses. Based on the resultant LD 50 values, C. terminifera [LD 50 = 417 (220-721) conidia/insect], was three times more susceptible than P. vittatum [LD 50 = 1,212 (689-1900) conidia/insect], though this difference was not significant (P > 0.05). Molting within 24 h of inoculation had no effect on subsequent mortality. The high susceptibility of the two most important acridid pests in Australia to a locally derived isolate encourages the development of M. flavoviride as a more environmentally benign alternative to fenitrothion spraying.