LONG-TERM FIELD EFFICACY OF THE ENTOMOGENOUS FUNGUS METARHIZIUM-ANISOPLIAE AGAINST THE SUBTERRANEAN SCARAB, ADORYPHORUS-COULONI

The efficacy of Metarhizium anisopliae DAT F-001 against Adoryphorus c ouloni was examined over 4 years on a sheep grazing property ('Inverel l') in central Tasmania. Three generations of the primary A. couloni p opulation and two generations of the overlapping population were studi ed. Application of 5.1 +/- 0.7 x 10(4) M. anisopliae spores g(-1) of s oil (2 cm below the soil surface), during midwinter 1989, when the pri mary population was in the middle of the L3 larval stage, resulted in 30.3% fewer larvae in treated plots by 21 weeks and 57.8% less pupae b y 27 weeks. The population decline was consistent with a mortality, mo del developed from laboratory data. In the two subsequent generations of the primary population, there were 63.2% (1991) and 45.0% (1993) fe wer larvae in the treated plots before the damaging L3 stage. The two sequential generations of the overlapping A. couloni larval population s had 68% (1990) and 65% (1992) fewer larvae in the treated plots than in the untreated plots. Reductions in larval numbers led to a greater retention of sown perennial grasses, reduced weed invasion and a 23% increase in pasture productivity in the autumn of 1992. Incorporation of M. anisopliae into the soil did not reduce the numbers of non-targe t invertebrates. The level of M. anisopliae DAT F-001 in the pasture r emained at levels close to the applied concentration (5.1 +/- 0.7 colo ny-forming units g(-1) of soil), bur increased 10-fold when mummified L3 larval, prepupal and pupal cadavers were present from January to Ju ne 1990. The level of the fungus in the soil was still twice the origi nal applied concentration at the conclusion of sampling in March 1992.