METARHIZIUM FLAVOVIRIDE (F1985) AS A PROMISING MYCOINSECTICIDE FOR AUSTRALIAN ACRIDIDS

Only one isolate of Metarhizium flavoviride Gams and Roszypal group 3 has been isolated from a field-infected acridid in Australia. This is isolate FI985 (ARSEF 324) obtained from a spur-throated locust, Austra cris guttulosa (Walker), near Rockhampton, Queensland, in 1979. In ter ms of conidial size and shape as well as phialide morphology, FI985 is intermediate between Metarhizium anisopliae (Metschnikoff) Sorokin an d M. flavoviride. It has been compared with other group 3 isolates usi ng RAPDs and sequence analysis of the ITS region and found to be very similar. However the analysis shows that these group 3 isolates are ge netically closer to M. anisopliae than to M. flavoviride sensu stricto . Laboratory bioassays have shown that FI985 is virulent for five spec ies of acridid pests in Australia. Comparative bioassays with other is olates of Metarhizium, including other group 3 isolates from Africa an d Asia, have not yet revealed any isolate more virulent than FI985. Th is isolate is amenable to mass-production on rice and has been formula ted in oil as a mycoinsecticide. The results from six field tests, mos tly against wingless grasshopper, Phaulacridium vittatum (Sjostedt), u sing, doses of 2-7x10(12) conidia per hectare and plot sizes up to 50 ha are summarized. These trials (with the exception of the first again st the Australian plague locust) have given high levels of disease-rel ated mortality in caged samples of the target collected within 3 days of spraying. In the four trials with wingless grasshopper, population reductions were detected 10-30 days after application; however these r eductions were much less than suggested by cage samples as a result of movement of the target acridids. In contrast, positive control plots sprayed with fenitrothion gave a very high initial kill (>90% in 1 day ) but were then more rapidly reinvaded. Consequently, 3-4 weeks after spraying the density in the plots treated with chemical insecticide an d those treated with mycoinsecticide were similar. Further field trial s are needed especially against the Australian plague locust and evalu ating lower doses. The results obtained to date show that a mycoinsect icide based on FI985 is likely to be effective over a wide range of ta rget acridids and weather conditions.