Microbial control of Schistocerca americana (Orthoptera: Acrididae) by Metarhizium flavoviride (Deuteromycotina): instar dependent mortality and efficacy of ultra low volume application under greenhouse conditions

The entomopathogenic fungus Metarhizium flavoviride Gams and Rozsypal has been widely tested for the suppression of African grasshoppers, but there has been no research on Nearctic species. We examined the potential of M. flavoviride for the control of the American grasshopper, Schistocerca americana (Drury). When tested under conidial dosages of 1.2 X 10(3), 1.2 X 10(4), and 1.2 X 10(5), 4th-instar S. americana were significantly more susceptible to M. flavoviride than 6th-instar and adult S. americana. At the conidial dosage of 1.2 X 10(5), M. flavoviride produced 89.7, 12.8, and 17.6% mean mortality 7 d after treatment in 4th-instar, 6th-instar, and adult S. americana, respectively. By the 14th d after treatment, the M. flavoviride conidial dosage of 1.2 X 10(5) produced 99.4, 86.1, and 80.8% mean mortality in 4th-instar, 6th-instar, and adult S. americana, respectively. The LD50 estimates for M. flavoviride of 1.7 X 10(4) conidia for the 4th-instar, 1.3 X 10(4) conidia for the 6th-instar, and 3.1 X 10(4) conidia for the adult S. americana are generally greater than those used for other acridids. Furthermore, mortality in M. flavoviride-treated S. americana was positively dosage dependent, as described by mean percentage of cumulative mortality and LT50 estimates. Greenhouse trials evaluating ultra low volume application to grasshoppers, foliage, or grasshoppers and foliage produced from 78.1 to 92.0% mean mortality 14 d after treatment. In this simulated field trial, grasshoppers and M. flavoviride were exposed to temperatures ranging from 10 to 40 degrees C, which demonstrated the potential of M. flavoviride to be effective under large temperature fluctuations, as may occur in the field